bluuebunny/crossref_metadata_2025 huggingface dataset:
Periodicity and directionality in the propagation of epileptiform discharges across neocortex
Authors: Chervin R. D. , Pierce P. A. , Connors B. W.
Published: December 2017

1. The horizontal propagation of epileptiform discharges has been studied in slices of neocortex treated with high concentrations of bicuculline methiodide, an antagonist of the inhibitory transmitter gamma-aminobutyric acid (GABA). The cortical areas examined were: primary somatosensory (SmI) and motor (MI), and primary (area 17) and secondary (area 18) visual areas of rats, and area 17 of cats. In all of these areas an electrical stimulus evoked single, all-or-none paroxysmal field potentials (PFPs) that propagated across the entire width of the slice without decrement. 2. The velocity of PFP propagation was approximately 0.06-0.09 m/s when averaged over cortical distances of several millimeters. PFP propagation occurred equally well in both directions across a slice. 3. Measurement of PFP propagation at higher spatial resolution (100-180 micron intervals) revealed that velocity was not homogeneous within rat SmI, rat area 18 and cat area 17, but instead varied manyfold as horizontal position changed. In these areas of cortex, propagation patterns were spatially periodic; power spectra reveal that the dominant spatial frequencies were centered about 1 mm-1, with negligible contributions above 2 mm-1. Occasionally PFP propagation was discontinuous, skipping over a small region of cortex and arriving distally before propagating into the more proximal region. 4. In those cortices with periodic propagation patterns, PFP velocity was also strongly direction-dependent. Propagation patterns measured in opposite directions across the same strip of cortex displayed similar periodicities, but in many slices they were negatively correlated, i.e., the propagation pattern in one direction was antiphasic compared to that in the other direction. 5. In contrast, propagation velocity across the center of area 17 of the rat was relatively constant and not directional. Near the boundaries of areas 17 and 18, however, PFP velocity changed abruptly and became periodic within area 18. Similarly, velocity within rat MI was more constant and less directional than in the adjacent SmI. 6. The patterns of PFP propagation velocity are often spatially periodic, directionally asymmetric, and depend upon cortical area. We suggest that the periodic patterns reflect systematic variations in the length or density of horizontal excitatory connections. Alternatively, or concurrently, periodicities could arise from the patchy distributions of intrinsic connections that have been observed anatomically in many areas of neocortex.
Response of vestibular neurons to head rotations in vertical planes. I. Response to vestibular stimulation
Authors: Kasper J. , Schor R. H. , Wilson V. J.
Published: December 2017

1. We have studied, in decerebrate cats, the responses of neurons in the lateral and descending vestibular nuclei to whole-body rotations in vertical planes that activated vertical semicircular canal and utricular receptors. Some neurons were identified as vestibulospinal by antidromic stimulation with floating electrodes placed in C4. 2. The direction of tilt that caused maximal excitation (response vector orientation) of each neuron was determined. Neuron dynamics were then studied with sinusoidal stimuli closely aligned with the response vector orientation, in the range 0.02-1 Hz. A few cells, for which we could not identify a response vector, probably had spatial-temporal convergence. 3. On the basis of dynamics, neurons were classified as receiving their input primarily from vertical semicircular canals, primarily from the otolith organs, or from canal+otolith convergence. 4. Response vector orientations of canal-driven neurons were often near +45 degrees or -45 degrees with respect to the transverse (roll) plane, suggesting these neurons received excitatory input from the ipsilateral anterior or posterior canal, respectively. Some neurons had canal-related dynamics but vector orientations near roll, presumably because they received convergent input from the ipsilateral anterior and posterior canals. Few neurons had their vectors near pitch. 5. In the lateral vestibular nucleus, neurons with otolith organ input (pure otolith or otolith+canal) tended to have vector orientations closer to roll than to pitch. In the descending nucleus the responses were evenly divided between the roll and pitch quadrants. 6. We conclude that most of our neurons have dynamics and response vector orientations that make them good candidates to participate in vestibulospinal reflexes acting on the limbs, but not those acting on the neck.
Periodicity coding in the inferior colliculus of the cat. I. Neuronal mechanisms
Authors: Langner G. , Schreiner C. E.
Published: December 2017

1. Temporal properties of single- and multiple-unit responses were investigated in the inferior colliculus (IC) of the barbiturate-anesthetized cat. Approximately 95% of recording sites were located in the central nucleus of the inferior colliculus (ICC). Responses to contralateral stimulation with tone bursts and amplitude-modulated tones (100% sinusoidal modulation) were recorded. Five response parameters were determined for neurons at each location: 1) characteristic frequency (CF); 2) onset latency of responses to CF-tones 60 dB above threshold; 3) Q10 dB (CF divided by bandwidth of tuning curve 10 dB above threshold); 4) best modulation frequency for firing rate (rBMF or BMF; amplitude modulation frequency that elicited the highest firing rate); and 5) best modulation frequency for synchronization (sBMF; amplitude modulation frequency that elicited the highest degree of phase-locking to the modulation frequency). 2. Response characteristics for single units and multiple units corresponded closely. A BMF was obtained at almost all recording sites. For units with a similar CF, a range of BMFs was observed. The upper limit of BMF increased approximately proportional to CF/4 up to BMFs as high as 1 kHz. The lower limit of encountered BMFs for a given CF also increased slightly with CF. BMF ranges for single-unit and multiple-unit responses were similar. Twenty-three percent of the responses revealed rBMFs between 10 and 30 Hz, 51% between 30 and 100 Hz, 18% between 100 and 300 Hz, and 8% between 300 and 1000 Hz. 3. For single units with modulation transfer functions of bandpass characteristics, BMFs determined for firing rate and synchronization were similar (r2 = 0.95). 4. Onset latencies for responses to CF tones 60 dB above threshold varied between 4 and 120 ms. Ninety percent of the onset latencies were between 5 and 18 ms. A range of onset latencies was recorded for different neurons with any given CF. The onset response latency of a given unit or unit cluster was significantly correlated with the period of the BMF and the period of the CF (P less than 0.05). 5."Intrinsic oscillations" of short duration, i.e., regularly timed discharges of units in response to stimuli without a corresponding temporal structure, were frequently observed in the ICC. Oscillation intervals were commonly found to be integer multiples of 0.4 ms. Changes of stimulus frequency or intensity had only minor influences on these intrinsic oscillations.(ABSTRACT TRUNCATED AT 400 WORDS)
Convergence of retinal W-cell and corticotectal input to cells of the cat superior colliculus
Authors: Berson D. M.
Published: December 2017

1. Conduction velocities of retinotectal W-cell afferents were estimated from differences among latencies of collicular unit responses to supramaximal stimulation of the contralateral optic disk (OD), optic chiasm (OX), and ipsilateral optic tract (OT). W-cell afferents driving collicular neurons had very slowly conducting axons, nearly all below 8 m/s (mean = 5.3 m/s). These match the conduction velocities of W-cell axons terminating in the uppermost superficial gray layer and triggering juxtazonal potentials (JZPs). Such slow conduction velocities are typical of W-cells belonging to the W2 subclass ("phasic W-cells"), but are slower than nearly all W1 cells ("tonic W-cells"). 2. Most W-driven cells were activated at latencies longer than expected for monosynaptic input from these W-cell afferents. However, comparable delays were observed among JZPs, which signal monosynaptic excitation of collicular neurons by W-cell terminals. This suggests that the delayed activation of W-driven cells reflects slowed conduction in the preterminal segments of W-cell afferents rather than polysynaptic transmission of W-cell signals through intermediary neurons in the brain stem or cortex. Thus monosynaptic inputs from retinal W2 cells appear to drive most neurons of the superficial collicular layers. 3. Convergence of retinotectal W-cell and corticotectal pathways was assessed by recording responses of W-driven collicular cells to intracortical stimulation of area 17. The great majority of W-driven collicular cells were activated by cortical stimulation (41/52; 79%), indicating that such convergence is widespread. 4. The population of corticotectal cells influencing W-driven collicular cells may differ from that mediating Hoffmann's Y-indirect pathway. W-driven collicular cells were activated from the striate cortex at longer latencies (mean = 6.3 ms) than cells driven by the Y-indirect pathway (mean = 2.5 ms). In addition, cortically activated W-driven cells were common throughout the superficial gray layer, whereas cells driven by the Y-indirect input were encountered only in the deepest part of the superficial gray and below. 5. W2 cells, apparently the dominant retinotectal cell type, nearly all project contralaterally and are tuned for slow stimulus velocities. Thus the binocularity of W-driven collicular cells and their sensitivity to moderately fast stimulus motion probably reflect the convergent cortical input described here.
Voltage-dependent currents prolong single-axon postsynaptic potentials in layer III pyramidal neurons in rat neocortical slices
Authors: Thomson A. M. , Girdlestone D. , West D. C.
Published: December 2017

1. Using isolated slices of rat cingulate and sensorimotor cortex, intracellular recordings were obtained from pyramidal neurons in layer III. Simultaneous extracellular recordings were obtained from neurons in ventral layer III and layer IV. Spike-triggered averaging was employed to investigate synaptic connections from neurons in layers III/IV to pyramidal cells in layer III. 2. Of 701 simultaneously recorded pairs of neurons, comprising 699 extracellularly and 128 intracellularly recorded neurons, synaptic connections were demonstrated in 30 pairs. Of these, 29 were excitatory postsynaptic potentials (EPSPs) and 1, an inhibitory postsynaptic potential (IPSP). Single-axon EPSPs with a wide variety of amplitudes were recorded: the range recorded at membrane potentials between -68 and -72 mV was 0.079-2.3 mV. Comparing recordings obtained from different cells, EPSP amplitude was found to be independent of both the membrane resistance of the postsynaptic neuron and the EPSP time course; i.e., the largest EPSPs were not necessarily those recorded from neurons with the highest input resistance, nor those with the briefest time course. 3. Shape indices: width at half amplitude and rise-time, indicative of both proximal and distal synaptic locations were obtained. Normalized rise-times were between 0.1 and 2 times the membrane time constant and half-widths between 0.8 and 20 times. 4. The majority of postsynaptic neurons displayed nonlinear voltage relations typical of pyramidal neurons, and the contribution to EPSP shape of voltage-dependent currents was investigated. EPSP amplitude and duration were found to be dependent on membrane potential. The majority of single-axon EPSPs (26 of 29), increased in amplitude and duration with membrane depolarization over the range -95 - -50 mV, despite the significant decrease in driving force for the EPSP that would be expected to accompany such large depolarizations. This increase coincided with an increase in the amplitude of voltage responses to small injected current pulses. 5. It is concluded that the amplitude and time course of single-axon EPSPs recorded in cortical pyramidal somata are affected not only by the amplitude of the postsynaptic current and the location(s) of the synapse(s) relative to the soma, but also by voltage-dependent currents. The possibility that the increase in amplitude and duration of these EPSPs with membrane depolarization is due to N-methyl-D-aspartate receptor involvement is discussed.
Postsynaptic potentials recorded in neurons of the cat's lateral geniculate nucleus following electrical stimulation of the optic chiasm
Authors: Bloomfield S. A. , Sherman S. M.
Published: December 2017

1. We recorded intracellularly from X and Y cells of the cat's lateral geniculate nucleus and measured the postsynaptic potentials (PSPs) evoked from electrical stimulation of the optic chiasm. We used an in vivo preparation and computer averaged the PSPs to enhance their signal-to-noise ratio. 2. The vast majority (46 of 50) of our sample of X and Y cells responded to stimulation of the optic chiasm with an excitatory postsynaptic potential (EPSP) followed by an inhibitory postsynaptic potential (IPSP); these were tentatively identified as relay cells. We quantified several parameters of these PSPs, including amplitude, latency, time to peak (i.e., rise time), and duration. 3. Among the relay cells, the latencies of both the EPSP and action potential evoked by optic chiasm stimulation were shorter in Y cells than in X cells. Furthermore, the difference between the latencies of the EPSP and action potential was shorter for Y cells than for X cells. This means that the EPSPs generated in Y cells reached threshold for generation of action potentials faster than did those in X cells. The EPSPs of Y cells also displayed larger amplitudes and faster rise times than did those in X cells, but neither of these distinctions was sufficient to explain the shorter latency difference between the EPSP and action potential for Y cells. 4. The EPSPs recorded in relay Y cells had longer durations than did those in relay X cells. Our data suggest that the subsequent IPSP actively terminates the EPSP, which, in turn, suggests that the time interval between EPSP and IPSP onsets is longer in Y cells than in X cells. Furthermore, we found that, for individual Y cells, the latency and duration of the evoked EPSP were inversely related. These observations lead to the conclusion that the latency of IPSPs activated from the optic chiasm is relatively constant among Y cells and thus independent of the EPSP latencies. Thus the excitation and inhibition produced in individual geniculate Y cells may originate from different populations of retinogeniculate axons. 5. The IPSPs recorded in geniculate relay cells following optic chiasm stimulation could be divided into three groups based on their durations. The majority of both X and Y cells showed short-duration IPSPs, whereas the remainder of Y cells displayed medium-duration IPSPs, and the remaining X cells displayed long-duration IPSPs. A positive correlation was seen between the time to peak and duration of these IPSPs.(ABSTRACT TRUNCATED AT 400 WORDS)
Eye movements induced by linear acceleration on a parallel swing
Authors: Baloh R. W. , Beykirch K. , Honrubia V. , Yee R. D.
Published: December 2017

1. Horizontal and vertical eye movements were induced in normal human subjects by sinusoidal linear acceleration on a parallel swing. The swing frequency was 0.3 Hz and the peak horizontal and vertical acceleration ranged from 0.17 to 0.48 and 0.03 to 0.34 g, respectively. Eye movements were recorded with the scleral search coil technique. 2. With the subjects seated in the dark to stimulate the otolith-ocular reflex, swing displacement along the interaural axis induced horizontal eye movements with a mean sensitivity to translation (ST) (peak eye velocity/peak swing velocity) of 3.8 to 4.7 degrees/m and a mean phase shift (eye velocity re swing velocity) of -152 to -160 degrees. Vertical eye movements had ST and phase values comparable to those of the horizontal eye movements. When the subjects sat facing forward so that the horizontal linear accelerations occurred in the occipitonasal axis, almost identical vertical but no consistent horizontal eye movements were induced. In each case the horizontal and vertical eye movements were proportional to the horizontal and vertical displacement of the swing. 3. With the subject seated in the light looking to an earth-fixed target (synergistic visual-vestibular interaction), the gain (peak eye velocity/peak target velocity) of induced eye movements was near 1, and the phase was compensatory (i.e., approximately -180 degrees) for all stimuli (even at target velocities at which the pursuit gain was less than 1). Subjects were able to suppress the otolith-ocular responses by fixating on a target attached to the swing. The ST decreased by an order of magnitude compared with measurements in the dark without a fixation target. 4. Subjects were able to augment the ST (horizontal and vertical) by imagining an earth-fixed target. Halving the distance of the imagined target approximately doubled the ST. 5. In two of three subjects tested, the ST measured with mental alerting in the dark adaptively increased (approximately doubled) after 20 min of continuous synergistic visual-vestibular interaction. The subject who did not show an adaptive increase in ST began with the highest value of the 10 normal subjects. 6. We conclude that during linear accelerations of the head the otolith signal is correctly interpreted as head movement and not rotation of the gravity vector. The otolith-ocular reflex interacts with the visual pursuit system to improve ocular stability during translational head movements.
Rhythmic fluctuations of dorsal root potentials and antidromic discharges of primary afferents during fictive locomotion in the cat
Authors: Dubuc R. , Cabelguen J. M. , Rossignol S.
Published: December 2017

1. This study examines rhythmical activity of primary afferents occurring during "fictive" locomotion in decorticate paralyzed cats. Oscillations of the dorsal root potential (DRP) at the frequency of the locomotor rhythm have been observed at the lumbosacral and cervical levels. In addition, rhythmic antidromic discharges of primary afferent units have been recorded from the proximal stumps of cut dorsal root filaments. A detailed study of the relationships between the DRP fluctuations, the antidromic discharges, and the locomotor activity monitored by recording extensor and flexor muscle nerves is presented. 2. Typical DRP recordings from both lumbosacral and cervical levels show two negative waves (N1 and N2) separated by positive troughs (P1 and P2) in each locomotor cycle. Linear regression analyses indicate that the first negative wave (which generally has the largest amplitude) is related to the flexor activity whereas the second is related to the extensor activity. The relative amplitude of the two negative waves may vary without apparent concomitant changes in the recorded flexor or extensor motor nerves. The positive troughs occur respectively close to the period of transition between flexor and extensor activities and between extensor and flexor activities. 3. DRPs of similar period and amplitude can be observed in different ipsilateral roots recorded simultaneously. The DRPs recorded bilaterally from the same segment have the same periodicity but are out-of-phase. Point-to-point variations of amplitude in bilaterally recorded roots are not correlated. This suggests that the polarization of primary afferents on one side is mainly related to the locomotor events on that side. DRPs have been recorded in cats spinalized at Th13 and injected with nialamide and l-DOPA. This suggests that although the supraspinal contribution may be important, at least part of the DRPs may result from locomotor activity within the spinal cord itself. 4. A salient finding in our experiments was that of rhythmic antidromic unit discharges in the proximal stump of cut dorsal root filaments. Of the 194 units recorded, 19% (37/194) discharged in distinct bursts occurring at fixed times in the locomotor cycle. The majority of the units discharged either one burst during the period of flexor or extensor activity or one burst during one of the two periods of transition. Three units discharged two bursts per locomotor cycle. The frequency of the antidromic discharges of some units in one limb were also found to be modulated by stimulation of the skin or passive manipulation of the limbs.(ABSTRACT TRUNCATED AT 400 WORDS)
The accessory optic system of rabbit. I. Basic visual response properties
Authors: Soodak R. E. , Simpson J. I.
Published: December 2017

1. The response properties of accessory optic system (AOS) neurons were assessed using single-unit extracellular recording from each of the three AOS terminal nuclei [medial, lateral, and dorsal terminal nuclei (MTN, LTN, and DTN)] in the anesthetized rabbit. 2. AOS neurons had large, monocular (contralateral) receptive fields (tens of degrees on a side) and exhibited a pronounced selectivity to the speed and direction of movement of large, textured patterns. The greatest responses occurred at slow speeds on the order of 0.5 degrees/s. 3. MTN and LTN neurons responded best to movement in near vertical directions. However, the stimulus directions corresponding to the greatest excitation and the greatest inhibition both had a posterior component and, thus, the preferred excitatory and inhibitory directions were not opposite each other. DTN neurons responded most strongly to horizontal movement and were excited by temporal to nasal movement. 4. AOS neurons were unresponsive to natural vestibular stimulation presented as sinusoidal oscillations of the rabbit about the yaw, pitch, and roll axes. 5. The response properties of AOS neurons are remarkably similar to those of the ON, direction-selective ganglion cells of the rabbit retina, and therefore this class of ganglion cell is most likely the predominant, if not the only, direct retinal input to the AOS. The local direction-selective properties of AOS neurons can be accounted for by combining the tuning curves of ON, direction-selective ganglion cells in a simple manner. 6. The low speed preference of AOS neurons, along with their large receptive fields suggests that they are suited to complement the vestibular system in detecting self-motion.
Spatial organization of visual messages of the rabbit's cerebellar flocculus. I. Typology of inferior olive neurons of the dorsal cap of Kooy
Authors: Leonard C. S. , Simpson J. I. , Graf W.
Published: December 2017

1. Single-unit responses to large-field visual stimuli were recorded extracellularly from neurons in the dorsal cap of Kooy of the inferior olive in anesthetized, paralyzed rabbits. The visually modulated neurons in the dorsal cap responded optimally to slow rotation of random dot stimuli, which were produced using handheld patterns or a planetarium projector. 2. Neurons had either monocular or binocular receptive fields. For binocular receptive field neurons, monocular stimulation of one eye, called the dominant eye, elicited greater modulation than did stimulation of the other eye. Rotation about a particular axis, called the preferred axis, produced both maximal excitation and inhibition. On the basis of differences in preferred axis orientation and in eye dominance, three neuron classes called Vertical Axis, Anterior (45 degrees) Axis, and Posterior (135 degrees) Axis were distinguished. 3. Vertical Axis neurons were modulated exclusively from the eye contralateral to the inferior olive recording site. This cell type responded strongly to large-field visual stimuli rotating about the vertical axis. Excitation resulted from movement in the temporal to nasal direction, and inhibition occurred during movement in the nasal to temporal direction. 4. Two subclasses of Anterior (45 degrees) Axis neurons were distinguished according to whether the receptive field was monocular or binocular. For both subclasses, the dominant eye was ipsilateral. The receptive field organization of the dominant eye was bipartite as described in the previous paper (51) for neurons in the midbrain visual tegmental relay zone. Anterior (45 degrees) Axis neurons were maximally excited when the stimulus pattern moved upward and posterior above the horizon in the anterior quadrant of the ipsilateral visual field, from 0 degrees (nose) to approximately 45 degrees azimuth. From 45 to 180 degrees azimuth (occiput) and above the horizon, these neurons were excited by downward and posterior movement. Inhibition occurred with oppositely directed movements. For rotating stimuli presented to the dominant eye, this class of neurons responded best to rotation of the visual world about an axis oriented near the horizontal plane and approximately 45 degrees azimuth. 5. The receptive field of Posterior (135 degrees) Axis neurons was always binocular, with the dominant eye contralateral. For the contralateral receptive field, from 0 degree (nose) to 135 degrees azimuth and above the horizon, excitation occurred during upward and posterior movement.(ABSTRACT TRUNCATED AT 400 WORDS)
Neural coding of gustatory information in the thalamus of Macaca mulatta
Authors: Pritchard T. C. , Hamilton R. B. , Norgren R.
Published: December 2017

1. Extracellular action potentials were recorded from single neurons in the parvicellular division of the ventroposteromedial (VPMpc) nucleus of the thalamus of restrained, but alert, Old World monkeys during gustatory, tactile, and thermal stimulation of the oral cavity. In contrast to previous reports in anesthetized or paralyzed rats, the spontaneous activity of these neurons was brisk and their evoked responses robust. 2. Each of 50 taste-responsive neurons was tested with 1.0 M sucrose, 0.1 M NaCl, 0.003 M HCl, and 0.001 M QHCl before other concentrations of the same stimuli were used. Sucrose, which was effective in 80% of the neurons tested, evoked the largest responses of the 4 standard gustatory stimuli (16.1 spikes/s). The average response to NaCl, an effective stimulus for 44% of the neurons in the sample, was 7.5 spikes/s. HCl and QHCl, which few neurons responded to, typically evoked smaller responses. 3. Most of the neurons tested showed monotonic intensity-response (I-R) functions. The power functions showed about the same degree of compression (range = 0.39-0.53), which has been described previously for brain stem neurons in anesthetized rodents. Only 9.1% of the responses were inhibitory, and there was no tendency for these responses to be associated with either specific neurons or stimuli. These data suggest that quality coding of gustatory information in the thalamus is not radically different from that seen among lower-order neurons in other species. 4. Through the use of hierarchical cluster analysis, it was possible to divide the neuron sample into 2 groups, one of which consisted of sucrose-best neurons that had an average entropy value of 0.56. The neurons in the other group, though more heterogeneous, showed either primary or side-band sensitivity to NaCl. The average breadth of responsiveness of the 50 thalamic neurons as described by the entropy coefficient was 0.73. 5. In addition to gustatory neurons, tactile (n = 15), thermal (n = 1), and nonresponsive (n = 25) neurons also were located within VPMpc. An additional 48 neurons that could not be classified as either sensory or motor in nature, inhibited their bursting spontaneous discharge just prior to the onset of fluid stimulation. Only 2 of these neurons demonstrated differential chemical sensitivity. The presence of these nongustatory neurons within the thalamic taste area suggests that the traditional characterization of VPMpc as a gustatory relay may understate its role in ingestive behavior and ignore other noningestive functions of the area.
A voltage-clamp study of isolated stingray horizontal cell non-NMDA excitatory amino acid receptors
Authors: O'Dell T. J. , Christensen B. N.
Published: December 2017

1. Horizontal cells enzymatically isolated from retinas of the Atlantic stingray (Dasyatis sabina) were voltage-clamped using the patch electrode in the whole-cell mode. A rapid microsuperfusion system was used to apply excitatory amino acid agonists and antagonists. 2. The isolated cells responded to glutamate (GLU), kainate (KA), quisqualate (QA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). Responses elicited by GLU, QA, and AMPA but not KA exhibited a concentration-dependent and concanavalin A- (Con-A) sensitive desensitization. No responses were elicited by aspartate, N-methyl-D-aspartate, or quinolinate at concentrations as high as 1.0 mM. 3. Judging from the concentration producing one-half of the maximal current response (EC50), the rank order affinities of the agonists was QA greater than or equal to GLU greater than AMPA greater than KA. Whereas KA had the lowest affinity of the agonists tested it was the most efficacious, producing the largest currents. Hill coefficients of the concentration-response data were near two for KA and GLU and near one for QA and AMPA. 4. The agonists differed in their sensitivity to various excitatory amino acid receptor antagonists. Kynurenate (KYN) produced a nearly complete block of horizontal cell responses to GLU and KA at concentrations that had little effect on QA and AMPA. Piperidine-2,3-dicarboxylic acid (cis-PDA), 1-(4-chlorobenzoyl)-piperazine-2,3-dicarboxylic acid (pCB-PzDA), and folic acid were less potent antagonists than KYN but were also better blockers of KA and GLU responses than of QA- and AMPA-elicited responses. 5. When QA, AMPA, or GLU were applied in combination with 55.0 microM KA the current was less than that produced by KA alone. The rank order potency for the inhibition of KA-elicited responses was QA greater than AMPA greater than GLU. In the presence of low concentrations of KA (1.0-20.0 microM), QA- and AMPA-elicited responses were potentiated. This potentiation was prevented by KYN. 6. Single-channel conductance and mean open time were estimated from the current noise fluctuations in the presence of agonist. The mean single-channel conductance for QA was 9 pS that was almost twice as large as the conductance for KA (5.9 pS) and GLU (5.7 pS). The mean open time in the presence of QA or GLU was approximately 1 ms, which was about one-half of that for KA (2.0 ms). 7. These results are best explained by the existence of a single receptor protein with multiple but not identical ligand-binding sites.(ABSTRACT TRUNCATED AT 400 WORDS)
Distribution of combination-sensitive neurons in the ventral fringe area of the auditory cortex of the mustached bat
Authors: Edamatsu H. , Kawasaki M. , Suga N.
Published: December 2017

1. The orientation sound (pulse) of the mustached bat, Pteronotus parnellii parnellii, consists of long constant-frequency components (CF1-4) and short frequency-modulated components (FM1-4). The auditory cortex of this bat contains several combination-sensitive areas: FM-FM, DF, VA, VF, and CF/CF. The FM-FM area consists of neurons tuned to a combination of the pulse FM1 and the echo FMn (n = 2, 3, or 4) and has an echo-delay (target-range) axis. Our preliminary anatomical studies with tritiated amino acids suggest that the FM-FM area projects to the dorsal fringe (DF) area, which in turn projects to the ventral fringe (VF) area. The aim of our study was to characterize the response properties of VF neurons and to explore the functional organization of the VF area. Acoustic stimuli delivered to the bats were CF tones, FM sounds, and their combinations mimicking the pulse emitted by the mustached bat and the echo. 2. Like the FM-FM and DF areas, the VF area is composed of three types of FM-FM combination-sensitive neurons: FM1-FM2, FM1-FM3, and FM1-FM4. These neurons show little or no response to a pulse alone, echo alone, single CF tone or single FM sound. They do, however, show a strong facilitative response to a pulse-echo pair with a particular echo delay. The essential components in the pulse-echo pair for facilitation are the FM1 of the pulse and the FMn of the echo.(ABSTRACT TRUNCATED AT 250 WORDS)
Long-lasting reduction of excitability by a sodium-dependent potassium current in cat neocortical neurons
Authors: Schwindt P. C. , Spain W. J. , Crill W. E.
Published: December 2017

1. The function and ionic mechanism of a slow outward current were studied in large layer V neurons of cat sensorimotor cortex using an in vitro slice preparation and single microelectrode voltage clamp. 2. With Ca2+ influx blocked, a slow relaxation ("tail") of outward current followed either (1) repetitive firing evoked for 1 s or (2) a small 1-s depolarizing voltage clamp step that activated the persistent Na+ current of neocortical neurons, INaP. When a depolarization that activated INaP was maintained, an outward current gradually developed and increased in amplitude over a period of tens of seconds to several minutes. An outward tail current of similar duration followed repolarization. The slow outward current was abolished by TTX, indicating it depended on Na+ influx. 3. With Ca2+ influx blocked, the onset of the slow Na+-dependent outward current caused spike frequency adaptation during current-evoked repetitive firing. Following the firing, the decay of the Na+-dependent current caused a slow afterhyperpolarization (sAHP) and a long-lasting reduction of excitability. It also was responsible for habituation of the response to repeated identical current pulses. 4. The Na+-dependent tail current had properties expected of a K+ current. Membrane chord conductance increased during the tail, and tail amplitude was reduced or reversed by membrane potential hyperpolarization and raised extracellular K+ concentration [( K+]0). 5. The current tail was reduced reversibly by the K+ channel blockers TEA (5-10 mM), muscarine (5-20 microM), and norepinephrine (100 microM). These agents also resulted in a larger, more sustained inward current during the preceding step depolarization. Comparison of current time course before and after the application of blocking agents suggested that, in spite of its capability for slow buildup and decay, the onset of the Na+-dependent outward current occurs within 100 ms of an adequate step depolarization. 6. With Ca2+ influx blocked, extracellular application of dantrolene sodium (30 microM) had no clear effect on the current tail or the corresponding sAHP.(ABSTRACT TRUNCATED AT 400 WORDS)
Norepinephrine selectively reduces slow Ca2+- and Na+-mediated K+ currents in cat neocortical neurons
Authors: Foehring R. C. , Schwindt P. C. , Crill W. E.
Published: December 2017

1. The effects of norepinephrine (NE) and related agonists and antagonists were examined on large neurons from layer V of cat sensorimotor cortex ("Betz cells") were examined in a brain slice preparation using intracellular recording, constant current stimulation and single microelectrode voltage clamp. 2. Application of NE (0.1-100 microM) usually caused a small depolarization from resting potential; hyperpolarizations were rare. Application of NE reversibly reduced rheobase and both the Ca2+- and Na+-dependent portions of the slow afterhyperpolarization (sAHP) that followed sustained firing evoked by constant current injection. The faster Ca2+-dependent medium afterhyperpolarization (mAHP), the fast afterhyperpolarization (fAHP), the action potential, and input resistance were unaffected. 3. The changes in excitability produced by NE application were most apparent during prolonged stimulation. The cells exhibited steady repetitive firing to currents that were formerly ineffective. The slow phase of spike frequency adaptation was reduced selectively and less habituation occurred during repeated long-lasting stimuli. The relation between firing rate and injected current became steeper if firing rate was averaged over several hundred milliseconds. 4. During voltage clamp in TTX, NE application selectively reduced the slow component of Ca2+-mediated K+ current. The faster Ca2+-mediated K+ current was unaffected, as were two voltage-dependent, transient K+ currents, the anomalous rectifier and leakage conductance measured at resting potential. Depolarizing voltage steps in the presence of Cd2+ revealed an apparent time- and voltage-dependent increase of the persistent Na+ current after NE application. The voltage-clamp results suggested ionic mechanisms for all effects seen during constant current stimulation except the depolarization from resting potential. The latter was insensitive to Cd2+ and TTX and occurred without a detectable change in membrane conductance. 5. NE application did not alter Ca2+ spikes evoked in the presence of TTX and 10 mM TEA. Inward Ca2+ currents examined during voltage clamp in TTX (with K+ currents reduced) became slightly larger after NE application. We conclude that NEs reduction of the slow Ca2+-mediated K+ current is not caused by reduction of Ca2+ influx. 6. Effects on membrane potential, rheobase, and the sAHP were mimicked by the beta-adrenergic agonist isoproterenol, but not by the alpha-adrenergic agonists clonidine or phenylephrine at higher concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)
Encoding of electrical, thermal, and mechanical noxious stimuli by subnucleus reticularis dorsalis neurons in the rat medulla
Authors: Villanueva L. , Bing Z. , Bouhassira D. , Le Bars D.
Published: December 2017

1. In anesthetized rats, recordings were made within the medullary subnucleus reticularis dorsalis (SRD) from neurons that exhibited convergence of nociceptive inputs from the entire body. Neurons with total nociceptive convergence (TNC) responded to suprathreshold percutaneous electrical stimuli (2-ms duration) with an early and a late peak due to activation of A delta- and C-fibers, respectively, no matter which part of the body was stimulated. Neurons with partial nociceptive convergence (PNC) responded to the same stimuli with an A delta-peak regardless of which part of the body was stimulated and with a C-peak of activation from some, mainly contralateral, parts of the body. The characteristics of the responses of these neurons to the application of graded intensities of electrical, thermal, and mechanical stimuli were analyzed. 2. All TNC neurons and 85% of PNC neurons responded to A delta- and C-fiber activation following percutaneous electrical stimulation of the contralateral hindpaw. With regard to A delta-fiber-evoked responses, a linear relationship between the logarithm of the applied current and the magnitude of the responses was found within the 0.25- to 6.0-mA and 0.5- to 24-mA ranges for TNC and PNC neurons, respectively; however, these curves were essentially similar. With regard to C-fiber-evoked responses, such a linear relationship was found within the 1.5- to 6.0-mA range for both types of SRD neurons, although the TNC neurons presented larger C-fiber-evoked responses than did the PNC neurons. 3. TNC and PNC neurons linearly increased their discharges during the application of noxious thermal stimuli to the contralateral hindpaw within the range 44-52 degrees C; the mean responses evoked by noxious heat from TNC neurons were of higher magnitude than those from PNC neurons. The majority of SRD neurons presented long-lasting afterdischarges, especially with the highest temperature employed (52 degrees C). 4. TNC neurons monotonically increased their discharges during graded mechanical or thermal stimulation of the tail. When mechanical stimuli were applied, a linear relationship was found between the logarithm of the strength of the mechanical stimulus and the neuronal discharges, in the 5.3- to 7.4-N/cm2 range. With thermal stimulation, TNC neurons linearly increased their discharges in the 44-52 degrees C range. When increasing amounts of the tail were immersed in a 50 degrees C waterbath, TNC neurons increased their discharges within a restricted range of tail surface areas (0.9-5.7 cm2); further increases in the stimulated surface size were not followed by increases in firing rate.(ABSTRACT TRUNCATED AT 400 WORDS)
Urinary bladder and hindlimb afferent input inhibits activity of primate T2-T5 spinothalamic tract neurons
Authors: Brennan T. J. , Oh U. T. , Hobbs S. F. , Garrison D. W. , Foreman R. D.
Published: December 2017

1. Extracellular recordings were made from 41 spinothalamic tract (STT) neurons on the left side of the T2-T5 spinal segments of 20 monkeys (Macaca fascicularis) anesthetized with alpha-chloralose. Manipulation of the left triceps-chest region and electrical stimulation of cardiopulmonary sympathetic afferent fibers excited these cells. 2. Isotonic urinary bladder distensions (UBD) to pressures between 20 and 80 cmH2O reduced the spontaneous activity in 33 of 41 cells. Cell activity was significantly reduced by UBD at 20 cmH2O. Distensions to 40, 60, and 80 cmH2O produced progressively greater reductions in spontaneous discharge. Activity was decreased throughout distension in 29 cells (tonic inhibition) and at the onset of distension in 3 neurons (phasic inhibition). In one cell, inhibition followed a brief excitation at the onset of distension (phasic excitation-tonic inhibition). Spontaneous bladder contractions also inhibited STT cell activity. 3. Inhibition by UBD was observed in STT cells characterized as wide dynamic range, high threshold, and high threshold inhibitory. No correlation existed between cell type or laminar location and inhibition by urinary bladder distension. Cells excited by cardiopulmonary sympathetic afferent A delta- and C-fibers had a significantly greater tendency to be inhibited by UBD (17 of 18) than cells activated by A delta- but not C-fibers (13 of 20). 4. Urinary bladder distension and pinch of the hindlimbs also reduced activity of STT cells excited by input from cardiopulmonary sympathetic afferents and from the proximal forelimb. 5. Urinary bladder distension to 40, 60, or 80 cmH2O produced a greater absolute but smaller relative reduction in the firing frequency of STT cells as spontaneous activity increased. Thus the magnitude of this inhibitory effect may depend on whether the inhibitory effect is measured as an absolute or relative change in cell activity. 6. Convergent inhibitory input from somatic regions also was observed. Noxious pinch of the hamstring region of the right hindlimb decreased activity in 32 of 39 cells. Left hindlimb pinch inhibited 21 of 38 cells, and 15 of 29 cells were inhibited by right triceps pinch. 7. Convergent inhibitory input from the hamstring region of the hindlimbs and from the urinary bladder to upper thoracic STT cells may be important for coding the intensity and location of noxious visceral and somatic stimuli and for organizing the appropriate sequence of motor responses when multiple noxious stimuli are present.
Electrophysiological properties and synaptic responses in the deep layers of the human epileptogenic neocortex in vitro
Authors: Avoli M. , Olivier A.
Published: December 2017

1. Neocortical slices of the first and second temporal gyrus and frontal lobe, removed in human epileptic patients for the relief of intractable seizures, were maintained in vitro at 35 +/- 1 degrees C. Electrophysiological properties of neurons in the deep layers (1,800–2,600 micron below the pial surface) were studied with conventional intracellular recording and stimulation techniques. Synaptic responses were evoked by extracellular focal stimuli. Intracellular injections of some cells with the fluorescent dye Lucifer yellow revealed large spiny pyramidal neurons. 2. Values of input resistance, resting membrane potential (Vm), and action-potential amplitude were similar for neurons in different cortical regions. These parameters were also similar when neurons were grouped in accordance to the degree of electrographic epileptiform activity displayed by the cortical tissue in situ. 3. Inward rectification occurred when neurons were depolarized by 5–15 mV positive to the resting Vm. This rectification was abolished by extracellular application of tetrodotoxin (TTX, 1 microM), but was still observed in the presence of the Ca2+-channel blocker Cd2+ (2 mM). Pulses of hyperpolarizing current elicited a slowly developing inward rectification, called anomalous rectification, which was insensitive to TTX, but blocked by extracellular application of Cs+ (1-2 mM). 4. Intracellular injection of depolarizing square pulses of current (0.1-4 s) evoked repetitive firing. In most cells the firing rate decreased smoothly for tens of milliseconds (i.e., it adapted) before reaching a steady level. Plots of the relation between frequency of the repetitive firing and injected current (f-I curve) displayed two linear segments for the early intervals as well as for the adapted and/or the steady firing. The slope of the initial, steeper linear segment of the f-I curve computed during the early intervals and during the adapted firing was 163 +/- 51 and 56 +/- 27 (SD) Hz/nA, respectively. 5. A long-lasting (up to 8 s) afterhyperpolarization (AHP) followed the repetitive firing induced by square pulses of depolarizing current. Its amplitude was directly proportional to the amount of current injected, it was sensitive to changes in the Vm, and it had an equilibrium potential 10–40 mV negative to the resting Vm. This value plus the fact that the AHP could be recorded with KCl-filled microelectrodes suggested that it was caused by an increase in conductance to K+ ions. Bath application of the Ca2+ channel blockers Cd2+ (2 mM) or Mn2+ (2 mM) decreased and eventually blocked the AHP.(ABSTRACT TRUNCATED AT 400 WORDS)
Analysis of synaptic events in the opossum piriform cortex with improved current source-density techniques
Authors: Rodriguez R. , Haberly L. B.
Published: December 2017

1. The piriform cortex of the opossum was studied by current source-density (CSD) analysis of field potentials to determine the laminar and temporal distribution of synaptic currents evoked by lateral olfactory tract (LOT) stimulation. 2. Extracellular conductivity was measured as a function of depth at high resolution and incorporated into CSD computations. Inclusion of the conductivity term resulted in relatively subtle changes in the shapes of CSD profiles. Resolution and accuracy of CSD computations was further improved by use of a new smoothing approach and averaging of multiple potential profiles obtained at the same site. 3. The CSD depth profile resulting from LOT stimulation revealed six major synaptic events that were consistently present at anterior, middle, and posterior sites: one during the first (A1) peak of the initial surface negative dichrotic field potential component, three during the second (B1) peak, one during the surface positive field potential component (period 2), and one during the second surface negative component (period 3). In addition, CSD profiles were computed for the population spike generated by synchronous discharge of action potentials. Depths of the net inward and outward membrane currents underlying these events were correlated with the cortical lamination as determined histologically by placement of small dye marks. 4. In agreement with previous reports it is concluded that the large inward membrane current in layer Ia during the A1 wave underlies a monosynaptic EPSP evoked in distal apical dendritic segments of pyramidal cells by afferent fibers. This EPSP displays a marked paired shock facilitation. 5. Based on anatomic and physiological considerations it is concluded that the three spatially and temporally distinct inward membrane currents (sinks) that were observed in layers III, superficial Ib, and mid- to deep-Ib during the B1 wave, underlie disynaptic EPSPs resulting from direct synaptic interactions between pyramidal cells. It is postulated that the layer III sink is generated in basal dendrites largely via local axon collaterals, the superficial layer Ib sink in intermediate apical dendritic segments by association fibers originating in the anterior piriform cortex, and the deep Ib sink in proximal apical segments by association fibers originating largely in the posterior piriform cortex. 6. The latencies of the layer Ia and superficial layer Ib sinks (presumed mono- and large disynaptic EPSPs, respectively) increased from anterior to posterior. Amplitude of the superficial Ib sink relative to the Ia sink increased from anterior to posterior.(ABSTRACT TRUNCATED AT 400 WORDS)