bluuebunny/crossref_metadata_2025 huggingface dataset:
Task dependent patterns of muscle activation at the shoulder and elbow for unconstrained arm movements
Authors: Hong D. A. , Corcos D. M. , Gottlieb G. L.
Published: December 2017

1. Six subjects performed three series of pointing tasks with the unconstrained arm. Series one and two required subjects to move as fast as possible with different weights attached to the wrist. The first required flexion at both shoulder and elbow joints. The second required shoulder flexion and elbow extension. The third series required flexion at both joints and subjects were intentionally instructed to vary movement speed. These three pointing tasks were selected as the simplest progression from single to multiple degree of freedom movements in which different patterns of motoneuron excitation are required depending on whether movements are made against different loads or at different intended speeds. 2. Changes in load and changes in intended speed both produced systematic but different changes in the patterns of muscle activity and joint torque in both the elbow and shoulder muscles. These patterns are the same found during constrained, single-joint elbow flexion movements. The changes are expressed in the rates of rise, durations, and latencies of the electromyographic (EMG) bursts and in the rates of rise of torque that have specific dependencies based on the force requirements of the task. 3. A consistent, almost linear relationship is observed between muscle torque at the shoulder and at the elbow for all three tasks. Similar systematic changes were not seen in the kinematic description of joint angles.(ABSTRACT TRUNCATED AT 250 WORDS)
Primate frontal eye field activity during natural scanning eye movements
Authors: Burman D. D. , Segraves M. A.
Published: December 2017

1. As we scan an image, saccadic eye movements direct our vision to features that attract our attention. Although it is likely that the frontal eye field (FEF) cortex is an important component of the system generating those movements, most studies of FEF neuronal activity have relied upon visuomotor tasks where the experimental subjects are constrained to look from one spot of light to another. In this study, single-unit activity was recorded in the FEF while monkeys freely scanned a variety of projected images, and that activity was compared with activity evoked during conventional visuomotor tasks. 2. FEF neurons with visual activity in conventional tasks increased their activity during scanning when a portion of the image within their receptive field was targeted for the next saccade, but decreased their activity when a target was chosen outside of the receptive field. 3. FEF neurons with movement-related activity during conventional tasks were also active in association with saccades made during scanning. 4. Visual and movement activity were also studied by creating a task that approximated the conditions during the scanning paradigm (rescan task). This was done by superimposing a moveable spot of light onto the image that had been scanned, and rewarding the monkey for following the light as it recreated the original scan's spatial and temporal pattern of eye fixations. In contrast to the visual activity of neurons during the scanning paradigm, visual activity during the rescan task was unaffected by portions of the image within the cell's receptive field, but increased in response to the appearance of the target light.(ABSTRACT TRUNCATED AT 250 WORDS)
Variant firing patterns in rat hippocampal pyramidal cells modulated by extracellular potassium
Authors: Jensen M. S. , Azouz R. , Yaari Y.
Published: December 2017

1. The distribution of distinctive firing modes within the population of CA1 pyramidal cells and their modulation by the extracellular concentration of potassium ([K+]o) were investigated with intracellular recordings in rat hippocampal slices. 2. Pyramidal cells were injected with long (> 250 ms) and brief (3-5 ms) positive current pulses of increasing intensity. In normal [K+]o (3.5 mM), most cells (38 of 46 cells; 83%) were regular spiking neurons (generating accommodating trains of independent action potentials during long depolarizations and a single spike in response to brief stimuli). The remaining pyramidal cells (8 of 46; 17%) displayed differential tendencies to generate stereotyped clusters of action potentials, or bursts, according to which they were grouped into three subsets of endogenous bursters: grade I, bursting only when stimulated with long depolarizing current pulses (6 of 46; 13%); grade II, bursting also in response to brief stimulation (1 of 46; 2%); grade III, bursting also spontaneously even in absence of synaptic transmission (1 of 46; 2%). 3. Raising [K+]o from 3.5 to 7.5 mM (high [K+]o) significantly reduced resting membrane potential and input impedance but did not change the threshold potential for eliciting an action potential. 4. Raising [K+]o to 7.5 mM reversibly converted many regular spiking cells to bursters. Likewise, the burst tendency of normally bursting pyramidal cells increased to a higher grade in high [K+]o. Consequently, the fraction of bursters in high [K+]o (17 of 41 cells; 42%) was approximately 2.5-fold higher than in normal [K+]o and their differential distribution was shifted toward higher grades of bursting.(ABSTRACT TRUNCATED AT 250 WORDS)
Neuronal selectivities to complex object features in the ventral visual pathway of the macaque cerebral cortex
Authors: Kobatake E. , Tanaka K.
Published: December 2017

1. To infer relative roles of cortical areas at different stages of the ventral visual pathway, we quantitatively examined visual responses of cells in V2, V4, the posterior part of the inferotemporal cortex (posterior IT), and the anterior part of the inferotemporal cortex (anterior IT), using anesthetized macaque monkeys. 2. The critical feature for the activation was first determined for each recorded cell by using a reduction method. We started from images of three-dimensional complex objects and simplified the image of effective stimuli step by step by eliminating a part of the features present in the image. The simplest feature that maximally activated the cell was determined as the critical feature. The response to the critical feature was then compared with responses of the same cell to a routine set of 32 simple stimuli, which included white and black bars of four different orientations and squares or spots of four different colors. 3. Cells that responded maximally to particular complex object features were found in posterior IT and V4 as well as in anterior IT. The cells in posterior IT and V4 were, however, different from the cells in anterior IT in that many of them responded to some extent to some simple features, that the size of the receptive field was small, and that they intermingled in single penetrations with cells that responded maximally to some simple features. The complex critical features in posterior IT and V4 varied; they consisted of complex shapes, combinations of a shape and texture, and combinations of a shape and color. 4. We suggest that local neuronal networks in V4 and posterior IT play an essential role in the formation of selective responses to complex object features.
ATP-induced inward current in neurons freshly dissociated from the tuberomammillary nucleus
Authors: Furukawa K. , Ishibashi H. , Akaike N.
Published: December 2017

1. Neurons in the tuberomammillary nucleus (TMN), which are considered to be histaminergic, were dissociated and their response to extracellularly applied ATP was investigated in the nystatin-perforated patch recording mode under voltage-clamp condition. 2. ATP induced a sustained inward current that was slowly desensitized at a holding potential of -60 mV. 3. The ATP response increased in a concentration-dependent manner. The half-maximum concentration (EC50) was 44 microM and the Hill coefficient was 1.8. 4. The potency of ATP analogues was in the order of ATP > or = 2-methylthio-ATP >> alpha, beta-methylene ATP > or = ADP. Neither adenosine nor AMP induced any response. The results suggest that the purinergic receptor in TMN neurons is P2y. 5. The current-voltage relationship for the 100 microM ATP showed a significant inward rectification at a potential more positive than -20 mV in an external solution with 150 mM Na+, but a significant rectification current was not observed in an external solution with 150 mM Cs+. The change in the reversal potential of the ATP response (EATP) to a 10-fold change of extracellular Na+ concentration was 56 mV, indicating that the ATP-induced current is highly selective for Na+ over Cl-. 6. The permeability ratio for cations was Na+:Li+:K+:Rb+: Cs+:Ca2+ = 2.16:1.36:1.68:1.54:1:2.55, indicating that the ATP-induced current is passing through the ligand-gated nonselective cation channel. 7. These results suggest that ATP has an excitatory effect on the TMN neurons by opening nonselective cation channels.
Spinothalamic and spinohypothalamic tract neurons in the cervical enlargement of rats. II. Responses to innocuous and noxious mechanical and thermal stimuli
Authors: Dado R. J. , Katter J. T. , Giesler G. J.
Published: December 2017

1. The goal of this study was to gather data that would increase our understanding of nociceptive processing by spinothalamic tract (STT) neurons that receive inputs from the hand and arm. Fifty neurons in the cervical enlargement of urethan-anesthetized rats were antidromically activated from the contralateral posterior thalamus. A stimulating electrode was moved systematically within an anterior-posterior plane in the thalamus until a point was located where the smallest amount of current antidromically activated the neuron. The antidromic thresholds at each of these lowest threshold points was < or = 30 microA; the mean antidromic threshold was 15.4 +/- 1.0 (SE) microA. Lowest threshold points were found primarily in the posterior thalamic group (Po), zona incerta, and in or near the supraoptic decussation. 2. The recording sites of 47 neurons were marked and recovered. Recording sites were located in the superficial dorsal horn (SDH, n = 15), deep dorsal horn (DDH, n = 31), and ventral horn (n = 1). Recording sites were located across the mediolateral extent of the SDH. Within the DDH, recording sites were concentrated laterally in nucleus proprius and dorsally in the lateral reticulated area. The locations of the recording points confirm previous anatomic descriptions of STT neurons in the cervical enlargement. 3. Cutaneous excitatory receptive fields were restricted to the ipsilateral forepaw or forelimb in 67% (10/15) of the neurons recorded in the SDH and 42% (13/31) of the neurons recorded in the DDH. Neurons having larger, more complex receptive fields were also commonly encountered. Thirty-three percent (5/15) of the neurons recorded in the SDH and 58% (18/31) recorded in the DDH had receptive fields that were often discontinuous and included areas of the ipsilateral shoulder, thorax, and head, including the face. 4. Innocuous and noxious mechanical stimuli were applied to the receptive field of each neuron. Fifty percent (25/50) responded to innocuous mechanical stimuli but responded at higher frequencies to noxious stimuli (wide dynamic range, WDR). Forty-four percent (22/50) responded only to noxious stimuli (high threshold, HT). Six percent (3/50) responded preferentially to innocuous stimuli (low threshold, LT). WDR and HT neurons were recorded in both the SDH and DDH, including nucleus proprius, an area not typically associated with nociceptive transmission at other levels of the cord. Sixty percent (9/15) of the units recorded in the SDH were classified as WDR neurons; the other 40% (6/15) were classified HT. Forty-eight percent (15/31) of the units recorded in the DDH were classified as WDR neurons and 42% (13/31) as HT.(ABSTRACT TRUNCATED AT 400 WORDS)
Noise analysis of miniature IPSCs in adult rat brain slices: properties and modulation of synaptic GABAA receptor channels
Authors: De Koninck Y. , Mody I.
Published: December 2017

1. The properties of synaptic gamma-aminobutyric acid (GABA)A receptor channels were resolved by using tight-seal, whole-cell recordings from granule cells of the dentate gyrus in adult rat hippocampal slices and by applying the technique of nonstationary noise analysis to study miniature inhibitory postsynaptic currents (mIPSCs) recorded in the presence of tetrodotoxin (TTX), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and D-2-amino-5-phosphonovaleric acid (D-AP5). This technique allowed us to extract information about the conductance, the number, and the kinetics of ligand gated channels underlying elementary synaptic currents. 2. To ascertain the validity of the nonstationary noise analysis method we have first tested it on computer simulated mIPSCs with different channel activation, lifetime kinetics, and opening probabilities. Using intraburst mean open times, shorter than the time to the first opening following activation, caused a large variance at the peak due to the stochastic channel properties. This resulted in a skewed mean current-variance relationship, which precluded proper estimation of unit conductance and especially the number of channels open at the peak of mIPSCs. Regardless of the probability of channel opening, accurate estimates of the unit conductance and the number of channels underlying each simulated mIPSC were obtained when channels had mean open times longer than the time to first opening. 3. Once the validity of the nonstationary analysis had been ascertained, it was used on mIPSCs recorded at 35 degrees C. The unit conductance of the synaptic GABAA channels was 28 +/- 1 (SE) pS and the average number of channels underlying mIPSCs was 46 +/- 4. The mean current-variance relationship was not skewed at higher amplitudes, suggesting that the intrinsic variance at the peak of the GABAA mIPSCs is low and that the open time of the channels is longer than the time to first opening. The estimated unit conductance of the channels was constant over a wide range of holding potentials. 4. The amplitude distribution of mIPSCs with rapid 10-90% rise times (290 +/- 20 microseconds) was clearly skewed towards low values. This skew was not due to filtering of electrotonically distant currents. Current-variance analysis revealed that the skewness resulted from differences in the number of GABAA receptor channels and not from the heterogeneity of unitary conductances at various synapses. Selection of mIPSCs with slower rise times yielded smaller unit conductance estimates.(ABSTRACT TRUNCATED AT 400 WORDS)
Temporal covariance of pre- and postsynaptic activity regulates functional connectivity in the visual cortex
Authors: Fregnac Y. , Burke J. P. , Smith D. , Friedlander M. J.
Published: December 2017

1. It has been suggested from mathematical models and in vivo experiments in the visual cortex that periods of temporal covariance of pre- and postsynaptic activity can lead to a potentiation or depression of synaptic efficacy. We directly tested this hypothesis in vitro in the guinea pig and cat visual cortex. 2. Intracellular recordings were made in brain slices from 63 neurons in layers 2-4 in bicuculline-free artificial cerebrospinal fluid. Twenty-nine cells (n = 25 from pigmented guinea pigs and 4 from cats) were taken through a complete series of control and test protocols to evaluate the covariance hypothesis. Some (n = 7) cells that were taken through the complete experimental protocols were also filled intracellularly with biocytin. Compound postsynaptic potentials (PSPs) were evoked by low-frequency (0.2-1.0 Hz), weak (20% of threshold intensity) stimulation of the cortical white matter and/or intracortical sites in layers 2-3. 3. In one series of experiments we paired PSPs with imposed coincident depolarizing (S+) or hyperpolarizing (S-) pulses (mean +/- 2.8 nA for 50-80 ms) of the postsynaptic neuron (n = 54 PSPs; > 1 pairing protocol was often run on an individual cell). Controls consisted of analyzing the same number of S+ or S- pairings but with long temporal delays [called fixed delay pairings (FDPs)] between the test pathway stimulation and the onset of the intracellular current pulse (120 ms) and pseudopairings (PP) consisting of evoked PSPs and delivery of intracellular current injection pulses in a phase-independent manner. Twenty-one of 54 PSPs subjected to pairing were significantly modified by the protocol. The S+ protocol significantly (P < 0.05, Kolmogorov-Smirnov test) increased the peak amplitudes of 8 of 22 PSPs (+20 to +55%); the S- protocol significantly decreased the peak amplitudes of 13 of 32 PSPs (-15 to -88%), whereas the FDP and PP protocols generally did not cause significant changes in the PSPs (0% and 4%, respectively). Significant changes in PSPs persisted in most cases for 10-20 min. 4. Another series of experiments consisted of evaluating for the same cell the effects of evoking a PSP from one stimulation site without concomitant postsynaptic activation and alternately evoking a PSP from the other stimulation site with S+ or S- pairing (n = 25 PSPs). Only the paired pathway showed the predicted effects on the PSP (S+ pairing causing an increase in peak PSP amplitude and S- pairing causing a decrease in peak PSP amplitude).(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of chronic spinalization on ankle extensor motoneurons. II. Motoneuron electrical properties
Authors: Hochman S. , McCrea D. A.
Published: December 2017

1. Intracellular recording and stimulation techniques were used in a comparison of electrical properties of triceps surae and plantaris motoneurons between unlesioned and 6-wk chronic spinal (L1-L2) cats. The primary analysis was restricted to 195 motoneurons with action potential heights > or = 80 mV. 2. Voltage transients resulting from short-duration current pulses (0.5 ms) were used to estimate membrane time constant (tau m) and equivalent cylinder electrotonic length (L). Although L was unchanged, tau m and the equalization phase time constant were significantly lower (17%) in motoneurons from chronic spinal preparations. Estimated total cell surface area was also reduced by 11%. The incidence of sag conductances, as judged from observations of the decay of voltage transients, increased from 3% to 29% after chronic spinalization. 3. Input resistance, as measured from either the amplitude of voltage responses to long-duration (50 ms) hyperpolarizing pulses (RinL) or from the area of the short-duration current pulse-induced voltage transients, was unchanged in the chronic spinal preparation. 4. Rheobase current was unchanged but threshold voltage (V Th) was increased in chronic spinal motoneurons. Increased V Th was not a result of membrane hyperpolarization because both mean action potential height (88 mV) and resting membrane potential (70 mV) were identical in both preparations. 5. The threshold current for action potential activation by short-duration (0.5 ms) current pulses increased 28% in chronic spinal preparations. This is consistent with the increase in V Th in the same motoneurons. 6. Measured V Th was identical to that calculated from the product of RinL and rheobase in the unlesioned preparation but was significantly larger than calculated V Th in chronic spinal preparations. This may indicate an increased incidence or magnitude of subthreshold rectification processes in motoneurons from chronic spinal preparations. These results in barbiturate-anesthetized preparations suggest that ankle extensor motoneurons are less excitable in the chronic spinal state. 7. Mean afterhyperpolarization duration was 10% shorter in motoneurons from chronic spinal preparations, whereas amplitude was unchanged. 8. Electrical properties were also compared in chronic spinal and unlesioned preparations using motoneurons with action potential heights of 60-79 mV. In these motoneurons with presumably poorer impalements there were no significant differences between unlesioned and chronic spinal preparations. 9. Ia monosynaptic excitatory postsynaptic potentials (EPSPs) recorded in the same motoneurons have decreased half-widths and rise times and increased amplitudes.(ABSTRACT TRUNCATED AT 400 WORDS)
Orientation-sensitive amacrine and ganglion cells in the rabbit retina
Authors: Bloomfield S. A.
Published: December 2017

1. Intracellular recordings were obtained from amacrine and ganglion cells in the isolated, superfused retina-eyecup preparation of the rabbit to test the orientation sensitivity of their responses. Cell identification was based on morphological criteria following injection of horseradish peroxidase (HRP) or N-(2-aminoethyl)-biotinamide hydrochloride (Neurobiotin) to visualize soma-dendritic architectures. 2. In terms of the physiological mechanisms generating their sensitivity, two types of orientation-sensitive amacrine cell and a single type of orientation-sensitive ganglion cell were found. These cell types were termed orientation selective and orientation biased. Cells were subtypes further into on- or off-center receptive-field categories. 3. The receptive fields of orientation-selective amacrine and ganglion cells were composed of two inhibitory fields that flanked the excitatory center receptive field along the preferred orientation. These inhibitory flanks produced a center receptive-field anisotropy with its major axis corresponding to the preferred orientation: either parallel or orthogonal to the visual streak. When a stimulus was oriented orthogonal to the preferred orientation (i.e., at the null orientation), the inhibitory fields were stimulated, resulting in a null inhibition that blocked the center-mediated excitation. Stimulation of these inhibitory flanks was absolutely essential to evoke the orientation selectivity of these cells. The null response reflected inhibition associated with a conductance increase and not disfacilitation. 4. Orientation-biased amacrine cells displayed a center receptive-field anisotropy with its major axis oriented either parallel or orthogonal to the visual streak. These cells preferred light stimuli oriented along the major axis of the center receptive field. However, whereas the excitatory response of these cells was reduced when a stimulus was rotated from the preferred orientation, there was no corresponding hyperpolarization. No null inhibition was detected even after modulation of the membrane potential with extrinsic current. 5. Although orientation-biased amacrine cells were morphologically heterogeneous, they all displayed dendritic arbors that were markedly elongated along an axis corresponding to their physiological preferred orientation. Thus it appears that the elongated dendritic fields of these cells may provide for the anisotropy of their center receptive fields and, in turn, their orientation sensitivity. 6. Orientation-selective amacrine cells formed a rather homogeneous morphological group of cells. These neurons displayed large, radially symmetric dendritic arbors with diameters averaging 1,100 microns. There were no asymmetries in their dendritic fields and thus no clear structural basis for their orientation selectivity. 7. In contrast, orientation-selective ganglion cells displayed diverse soma-dendritic architecture and thus could not be placed into a single morphological class.(ABSTRACT TRUNCATED AT 400 WORDS)
Influence of callosal activity on units in the auditory cortex of ferret (Mustela putorius)
Authors: Kitzes L. M. , Doherty D.
Published: December 2017

1. Callosal neurons in primary auditory cortex project heavily to regions of the contralateral homotopic field that are excited by stimulation of one or both ears and minimally to regions that are excited by stimulation of one ear and inhibited by stimulation of the other ear. The intent of this study is to begin assessing the function of this extensive intercortical projection in determining the response properties of single units in the recipient auditory cortex. 2. Callosal neurons in the right auditory cortex of barbiturate-anesthetized ferrets were stimulated electrically through a pair of monopolar microelectrodes that were separated by 2–3 mm and whose uninsulated tips were located 500 microns below the pial surface. Electrical stimuli consisted of a single 100-microseconds pulse delivered at a fixed intensity and temporal relationship to the onset of each of a set of monaural or binaural acoustic stimuli. Pulse amplitude was almost always < 350 microA. Acoustic stimuli consisted of 100-ms best-frequency tones delivered monaurally or binaurally at 1-s intervals. The influence exerted by electrical stimulation of the right auditory cortex on responses of single units isolated in the left auditory cortex was assessed by comparing responses evoked by the same acoustic stimuli delivered alone and when accompanied by the electrical stimulation. In addition, the latencies of discharges evoked by the electrical stimuli delivered alone were assessed. Three categories of influence were observed: suppression, excitation, and a mixed class consisting of both suppression and excitation. 3. Suppression was the most commonly observed influence of callosal input on acoustically evoked responses. Depending on the strength of the acoustic stimuli and electrical pulse and the temporal relationship between the two kinds of stimulation, responses to acoustic stimuli could be completely suppressed or reduced to a smaller version of the control responses. The duration of the inhibitory influence was often > 100 ms and the suppression was frequently effective at latencies of 2–4 ms. 4. Although unit activity was commonly excited by electrical stimulation of the right auditory cortex, facilitation of acoustically evoked responses was infrequently observed. Apparent facilitation usually was the result of the summation of acoustically and electrically evoked discharges.(ABSTRACT TRUNCATED AT 400 WORDS)
Chronic neocortical epileptogenesis in vitro
Authors: Hoffman S. N. , Salin P. A. , Prince D. A.
Published: December 2017

1. We used an in vitro model to explore critical aspects of chronic epileptogenesis. Partial neocortical isolations having intact blood supply were made in rat and guinea pig from postnatal day 7 to 34 and then examined 1 to 150 days later in standard brain slice preparations. 2. The epileptogenic potential of several different types of lesions was assessed. Slices containing transcortical (i.e., gray matter) lesions, with or without a contiguous white matter injury (i.e., “undercut”), developed chronic epileptogenesis after a latency of approximately 1–2 wk, manifested by evoked and spontaneous “interictal” discharges and evoked “ictal” events. The region of hyperexcitability did not extend beyond approximately 2 mm from the chronic transcortical lesion and was rarely observed in slices having only an apparent white matter injury. 3. Multiple recordings and current source density (CSD) analysis identified layer V as the source of the interictal discharge. 4. Significant differences in CSD profiles of the evoked interictal discharge occurred between chronically epileptogenic slices and control (noninjured) slices bathed in the convulsant, bicuculline methiodide, suggesting that mechanisms other than disinhibition must be involved in posttraumatic epileptogenesis. 5. Interictal events were blocked in most but not all chronically injured slices by application of the N-methyl-D-aspartate (NMDA) receptor antagonist D-2-amino-5-phosphonovalerate (D-AP5), suggesting that non-NMDA receptors were predominantly involved in some preparations. 6. This model of chronic epileptogenesis in vitro will be useful in studies relevant to mechanisms of posttraumatic epilepsy in man.
The electrotonic structure of regular-spiking neurons in the ventral cochlear nucleus may determine their response properties
Authors: White J. A. , Young E. D. , Manis P. B.
Published: December 2017

1. Intracellular recordings were obtained from neurons in parasagittal brain slices of the guinea pig ventral cochlear nucleus (VCN). The principal neurons of the VCN can be parceled into two categories. Regular-spiking (Type I) neurons have a linear current-voltage (I–V) relationship over a large range of intracellularly injected currents and fire tonically in response to suprathreshold depolarizing currents. Phasically spiking (Type II) neurons have a nonlinear I–V relationship and fire only phasically at the onset of a depolarizing current or offset of a hyperpolarizing current. Regular-spiking neurons have been shown to be of the stellate morphological type, whereas phasically spiking neurons have been shown to be bushy cells. 2. The electrotonic structure of regular-spiking neurons was studied by applying previously developed modeling techniques based on the somatic shunt model. In these techniques, physiological data are used to determine the set of parameters best describing the neuron. As predicted from previous theoretical investigations, the use of an anatomic constraint (somatic surface area) reduces the variance in estimates of model parameters, especially for the dendritic membrane time constant tau D. 3. Model representations of regular-spiking cells fall into two categories: those with (passive) somatic membrane properties that are nearly identical to those of the dendrite (8/15 cases), and those with a significant amount of somatic shunt (7/15). Estimates of tau D (mean = 7.7 ms) are lower than those often described in the literature. We argue that this low value of tau D may be related to the need of neurons in the auditory brainstem to operate at high firing rates and/or to encode audio-frequency temporal fluctuations. 4. Dendritic transfer functions were calculated as functions of synaptic location using somatic shunt representations of regular-spiking neurons. These transfer functions allow us to predict that mid-range auditory frequencies (approximately 1 kHz) are greatly attenuated, even for synapses near the soma. Thus it is suggested that the electrotonic architecture of regular-spiking cells creates sufficient low-pass filtering of synaptic inputs to reduce the synchronization of firing of these neurons to mid-frequency auditory stimuli.
Mechanical entrainment of fictive locomotion in the decerebrate cat
Authors: Kriellaars D. J. , Brownstone R. M. , Noga B. R. , Jordan L. M.
Published: December 2017

1. We examined the ability of muscular and joint afferents from the hip region to entrain fictive locomotion evoked by stimulation of the mesencephalic locomotor region in the decerebrate cat by mechanically imposed, sinusoidal hip flexion and extension movements. 2. A method is presented for qualitative and quantitative analysis of entrainment. 3. Hip joint capsular afferents were shown by denervation experiments to be unnecessary for mediating locomotor entrainment. 4. As the population of muscular afferents was progressively decreased by selective denervation, the strength of entrainment concomitantly decreased, even though a few as two small intrinsic hip muscles were still effective in producing entrainment. The ability to entrain locomotion was abolished with complete ipsilateral denervation. 5. Entrainment was observed with low amplitude hip angular displacement of 5–20 degrees, which would be expected to activate low-threshold, stretch-sensitive muscle afferents. 6. The extensor burst activity occurred during the period of imposed hip flexion, which corresponded to passive stretching and loading of the extensor muscles, while the flexor burst activity occurred during the latter portion of the imposed hip extension, which corresponded to passive stretching of the flexor muscles (when attached) and release of the extensors. During harmonic entrainment, the match of hip cycle duration and step cycle duration was accomplished by a variation in extensor electroneurogram (ENG) burst duration. These results are consistent with a positive feedback mechanism where low-threshold afferent activity from the extensor musculature is used by the rhythm generator to prolong the extension phase of locomotion. 7. A hip cycle frequency-dependent phase shift of ENG activity was observed. This may indicate that the locomotor rhythm generator is dependent on more than just static positional or threshold load information for modulation of the step cycle frequency and switching between flexion and extension phases. 8. Subharmonic forms of entrainment were observed when the number of innervated muscles was markedly reduced. The occurrence of subharmonic entrainment characterizes the locomotor rhythm generator as a nonlinear oscillator. 9. To modulate the stepping frequency, the afferent pathways responsible for entrainment must be directly connected to the neural circuitry responsible for rhythm generation. The rhythm generating interneurons must receive a high degree of convergence from afferents arising from a variety of muscles spanning the hip joint.
Effects of inhibition and dendritic saturation in simulated neocortical pyramidal cells
Authors: Bush P. C. , Sejnowski T. J.
Published: December 2017

1. We have used compartmental models of reconstructed pyramidal neurons from layers 2 and 5 of cat visual cortex to investigate the nonlinear summation of excitatory synaptic input and the effectiveness of inhibitory input in countering this excitation. 2. In simulations that match the conditions of a recent experiment, dendritic saturation was significant for physiological levels of synaptic activation: a compound excitatory postsynaptic potential (EPSP) electrically evoked during a depolarization caused by physiological synaptic activation was decreased by up to 80% compared with an EPSP evoked at rest. 3. Synaptic inhibition must be coactivated with excitation to quantitatively match the experimental results. The experimentally observed coactivation of inhibition with excitation produced additional current shunts that amplified the decrease in test EPSP amplitude. About 30% of the experimentally observed decrease in EPSP amplitude was caused by decreases in input resistance (Rin) due to synaptic conductance changes; a reduced driving force accounted for the remaining decrease. 4. The amount of inhibition was then increased by nearly an order of magnitude, to approximately 10% of the total number of inhibitory synapses on a typical cortical pyramidal cell. The sustained firing of this many inhibitory inputs was sufficient to completely suppress the firing of a neuron receiving strong excitatory input. However, this level of inhibition produced a very large reduction in Rin. Such large reductions in Rin have not been observed experimentally, suggesting that inhibition in cortex does not act to veto (shunt) strong, sustained excitatory input (of order 100 ms). 5. We propose instead that strong, transient activation (< 10 ms) of a neuron's inhibitory inputs, sufficient to briefly prevent firing, is used to shape the temporal structure of the cell's output spike train. Specifically, cortical inhibition may serve to synchronize the firing of groups of pyramidal cells during optimal stimulation.
Pharmacological similarity between the retinal APB receptor and the family of metabotropic glutamate receptors
Authors: Tian N. , Slaughter M. M.
Published: December 2017

1. We performed current-clamp and voltage-clamp experiments in the amphibian retina to examine the effects of 1-amino-1,3-cyclopentanedicarboxylic acid (1S,3R ACPD), which is a selective agonist for the family of metabotropic glutamate receptors. 2. 1S,3R ACPD was found to selectively block the light responses of ON bipolar cells. It did not suppress the responses of horizontal cells of OFF bipolar cells. It blocked ON but not OFF responses of third-order retinal neurons. 3. 1S,3R ACPD mimicked the effect of the photoreceptor transmitter at the ON bipolar synapse. It reduced an inward current by a decrease in conductance. 4. The action of 1S,3R ACPD was very similar to that of 2-amino-4-phosphonobutyrate (APB) both in terms of effects on the ON bipolar cell potential and conductance and in terms of the retinal network. This suggests that the APB receptor is a predominant synaptic metabotropic glutamate receptor in the retina. 5. The rank-order potency at the retinal APB receptor is APB > 1S,3R ACPD > ibotenate. Quisqualate appears to be inactive at this receptor. The pharmacology of the retinal APB receptor matches that of the cloned mGluR4 and mGluR6 metabotropic glutamate receptors. On the basis of the in situ localization of mGluR6 to the inner nuclear layer of the retina, the retinal APB receptor may be this cloned receptor protein. 6. The effects of the three other ACPD stereo isomers were examined. 1S,3S ACPD was a weak agonist at the APB receptor. 1R,3R ACPD was a potent agonist in the inner retina, but inactive in the outer retina. This fits the profile of N-methyl-D-aspartate agonists. 1R,3S ACPD was inactive.
Comparison of neuronal selectivity for stimulus speed, length, and contrast in the prestriate visual cortical areas V4 and MT of the macaque monkey
Authors: Cheng K. , Hasegawa T. , Saleem K. S. , Tanaka K.
Published: December 2017

1. Prestriate area V4 and the middle temporal area (MT) compose the first stage in which the ventral and dorsal visual cortical pathways are segregated. To better known the functional dichotomy between the two pathways at this level, we recorded cell responses from V4 and MT using anesthetized, immobilized macaque monkeys and compared the selectivity for speed of stimulus motion and stimulus length and the sensitivity to luminance contrast between the two areas. 2. V4 cells were as selective as MT cells for speed. The sharpness of tuning was not different between the two populations. The optimal speed varied widely in both areas, but both of the two distributions showed peaks at 32 degrees/s. 3. V4 and MT cells were similar in that about one-half of the cells (45% in V4 and 48% in MT) showed inhibition by long (16 degrees) bars. However, V4 cells preferred stimuli whose lengths were distributed around the lengths of the receptive field, whereas an overwhelming majority of MT cells preferred stimuli whose lengths were much shorter than the lengths of the receptive field. 4. The cutoff contrast at which one-half the maximum response was elicited was distributed widely in both areas, and the two distributions considerably overlapped. MT cells as a whole, however, were slightly more sensitive to the luminance contrast than V4 cells. 5. There was a tendency toward local clustering for cells with similar speed preferences in MT but not in V4. Pairs of MT cells recorded within 400 microns had smaller difference in the optimal speed than that of cell pairs taken randomly from the whole sample of MT cells.
Neural activity in cortical area MST of alert monkey during ocular following responses
Authors: Kawano K. , Shidara M. , Watanabe Y. , Yamane S.
Published: December 2017

1. We studied response properties of neurons in the superior temporal sulcus (STS) of behaving monkeys that discharged during brief, sudden movements of a large-field visual stimulus, eliciting ocular following. Most neurons responded to movements of a large-field visual stimulus with directional selectivity, preferring high stimulus speeds. Neurons were mostly recorded in the medial superior temporal area (MST) (187/250) and the middle temporal area (MT) (57/250). Further response properties were studied in the MST neurons. 2. Response latencies were measured when a large-field random dot pattern was moved in the preferred direction and preferred speed for each neuron. Eighty percent (120/150) of the neurons were activated “ 50 ms after the onset of the stimulus motion. In most cases (89%, 134/150), increased firing rates started before the eye movements, with 59% (88/150) starting ” 10 ms before the eye movements. 3. The relationship between the latency of neuronal responses and that of eye movements was studied in 59 neurons by changing the stimulus speed systematically (10–160 degrees/s). The latencies of both neuronal and ocular responses decreased as stimulus speed increased. As a result, the time difference between the response latencies for neuronal and ocular responses varied little with changes in stimulus speed. 4. Blurring of the random dot pattern, by interposing a sheet of ground glass, increased the latency of both neuronal responses and eye movements. 5. With the use of a check pattern instead of random dots, both neuronal and ocular responses began to decrease rapidly when the temporal frequency of the visual stimulus exceeded 20 Hz. At 40 Hz the neurons showed a distinctive burst-and-pause firing pattern, and the eye movements showed signs of oscillation. 6. The response properties of the MST neurons during ocular following were similar to those of the dorsolateral pontine nucleus (DLPN) neurons, reported previously. Our results indicate that the MST neurons may provide visual information to the DLPN neurons and may play a role in eliciting ocular following. 7. Responses during smooth-pursuit eye movement were studied in 55 MST neurons. Each of these neurons responded to the moving large-field visual stimulus, which elicited ocular following, and 40 of these neurons were activated during smooth pursuit in the dark. Response latencies during smooth pursuit were long in those neurons having different directional preferences during smooth pursuit and ocular following but were short for those having the same directional preferences during smooth pursuit and ocular following.(ABSTRACT TRUNCATED AT 400 WORDS)
A rhythmic modulatory gating system in the stomatogastric nervous system of Homarus gammarus. II. Modulatory control of the pyloric CPG
Authors: Nagy F. , Cardi P.
Published: December 2017

1. In the European rock lobster, Homarus gammarus, two bilaterally symmetrical pairs of commissural neurons, P and commissural pyloric (CP), evoke excitatory postsynaptic potentials in the neurons of the pyloric motor network. The present paper shows that the two commissural neurons also exert a modulatory control over the pyloric network. 2. The P and CP neurons were active during ongoing pyloric rhythms. Ongoing pyloric activity was terminated when the neurons were hyperpolarized to inhibit their firing. 3. When the pyloric network was quiescent, depolarizing either the P or CP neuron induced a robust pyloric rhythm. 4. We studied the actions of the P and CP neurons on individual pyloric neurons isolated in situ from network interactions by a photoinactivation techniques. The P neuron induced oscillatory properties in the pacemaker pyloric dilator (PD) neurons and the motor neuron, ventricular dilator (VD), whereas the CP neuron induced rhythmogenic properties in all the network neurons but VD. Together, the P-CP neurons modulated the entire pyloric network. The modulatory effects of the P-CP neurons did not outlast the duration of their discharge. 5. The P and CP neurons also controlled the firing frequency of all the pyloric neurons. They may, in addition, control phasing of the constrictor neurons discharges, but this effect was state-dependent and occurred only when the pyloric central pattern generator was functioning weakly. Their role in providing flexibility to the network operation appeared relatively limited. 6. We conclude that the P and CP neurons are good candidates for insuring long-term maintenance of pyloric network activity patterns.
A rhythmic modulatory gating system in the stomatogastric nervous system of Homarus gammarus. III. Rhythmic control of the pyloric CPG
Authors: Cardi P. , Nagy F.
Published: December 2017

1. Two modulatory neurons, P and commissural pyloric (CP), known to be involved in the long-term maintenance of pyloric central pattern generator operation in the rock lobster Homarus gammarus, are members of the commissural pyloric oscillator (CPO), a higher-order oscillator influencing the pyloric network. 2. The CP neuron was endogenously oscillating in approximately 30% of the preparations in which its cell body was impaled. Rhythmic inhibitory feedback from the pyloric pacemaker anterior burster (AB) neuron stabilized the CP neuron's endogenous rhythm. 3. The organization of the CPO is described. Follower commissural neurons, the F cells, and the CP neuron receive a common excitatory postsynaptic potential from another commissural neuron, the large exciter (LE). When in oscillatory state, CP in turn excites the LE neuron. This positive feedback may maintain long episodes of CP oscillations. 4. The pyloric pacemaker neurons follow the CPO rhythm with variable coordination modes (i.e., 1:1, 1:2) and switch among these modes when their membrane potential is modified. The CPO inputs strongly constrain the pyloric period, which as a result may adopt only a few discrete values. This effect is based on mechanisms of entrainment between the CPO and the pyloric oscillator. 5. Pyloric constrictor neurons show differential sensitivity from the pyloric pacemaker neurons with respect to the CPO inputs. Consequently, their bursting period can be a shorter harmonic of the bursting period of the pyloric pacemakers neurons. 6. The CPO neurons seem to be the first example of modulatory gating neurons that also give timing cues to a rhythmic pattern generating network.
Long-term potentiation of horizontal connections provides a mechanism to reorganize cortical motor maps
Authors: Hess G. , Donoghue J. P.
Published: December 2017

1. Field potential recordings were used in rat motor cortex (MI) slice preparations to investigate the potential for activity-dependent modifications in the effectiveness of synaptic connections formed by layer II/III horizontal projections. 2. Long-term potentiation (LTP) of synaptic efficacy in MI horizontal pathways could be produced at short (0.5 mm) and long (1.0 mm) distances by theta burst stimulation (TBS), but only during local, transient application of the gamma-aminobutyric acid-A (GABAA) receptor antagonist, bicuculline methiodide (bic) immediately before TBS. Mean increase of the field potential amplitude measured 25–35 min after LTP induction ranged between 24 and 34%. Cooperative effects of conjoint TBS of two horizontal pathways on LTP induction were observed. 3. These results demonstrate that persistent changes in the functional interactions of cortical neurons can arise by activity-dependent mechanisms within the local horizontal connections and suggest a likely mechanism to recognize cortical representation patterns.
Different voltage dependence of transient and persistent Na+ currents is compatible with modal-gating hypothesis for sodium channels
Authors: Brown A. M. , Schwindt P. C. , Crill W. E.
Published: December 2017

1. These experiments tested the hypothesis that the differing voltage dependence of the transient (INa) and persistent (INaP) Na+ currents in neocortical neurons results from the state of inactivation of one type of Na+ channel rather than from the existence of different types of Na+ channels. This question was examined in acutely isolated pyramidal neurons from the sensorimotor cortex of rats by using papain to remove inactivation from INa and comparing the resulting activation curve with that of INaP. 2. In control cells, INaP activated at more negative potentials than INa. Inclusion of papain in the recording pipette removed inactivation from INa and caused the INa activation curve to be shifted leftward to the position of the curve for INaP measured in control cells. Papain greatly increased both INa amplitude and the time to reach peak INa during smaller depolarizations, whereas the difference between control and test currents was reduced during large depolarizations. 3. We conclude that differences in the voltage dependence of INa and INaP activation does not provide sufficient evidence that these currents flow through separate sets of Na+ channels. Instead, our results are consistent with the idea that INaP largely arises from a fraction of the transient Na+ channels that intermittently lose their inactivation.