bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrophysiological evidence for a bisynaptic retinocerebellar pathway
Authors: Ariel M. , Fan T. X.
Published: December 2017

1. Electrical microstimulation was applied to an in vitro turtle brain preparation while recording extracellular activity from the cerebellar cortex. A visual input to the cerebellum was investigated by measuring spike responses evoked by stimulation of drifting visual patterns imaged onto the contralateral retinal eyecup. A vestibular input was assessed by extracellular field potentials following brief current pulses through monopolar suction electrodes holding the eighth cranial nerve (nVIII). 2. The cortical topography of visual and vestibular inputs was first examined. Visual units and vestibular fields show considerable topographic overlap in the rostrolateral quadrant of the cerebellum. In addition, granule layer units were isolated that responded to current stimulation of nVIII (60-150 microA monopolar). In some cases, spikes occurred at short and fixed latency after each current pulse for stimulus frequencies of 100 Hz. The responses of these units suggest a direct path between the stimulating and recording electrodes without intervening synapses. Alternatively, extracellular units were also encountered that responded with longer, more variable latencies but only for low stimulation frequencies (< or = 20 Hz). Of the units that responded to nVIII stimulation, three units also responded to visual stimuli, yet those units all failed to follow high-frequency stimulation of nVIII. This cortical area may then be a site for convergence of visual and vestibular signals on postsynaptic cells. 3. The cellular identity of the visual units in the granule layer and the visual pathways leading there were next investigated.(ABSTRACT TRUNCATED AT 250 WORDS)
Timing of odor stimulation does not alter patterning of olfactory bulb unit activity in freely breathing rats
Authors: Sobel E. C. , Tank D. W.
Published: December 2017

1. The effect of the timing between nasal airflow and ongoing tracheal respiration on single-unit activity in the olfactory bulb (OB) of the rat was examined. Nasal and tracheal breathing were dissociated with the use of a double tracheal cannulation technique that allowed independent control of nasal airflow and control of the synchronization of nasal airflow and tracheal breathing. 2. When amyl acetate-saturated air was presented to the nose, OB units showed a distinct reorganization of activity known as respiratory patterning. Of 43 cells examined, 29 fired maximally after inspiration, and 14 fired maximally after expiration. In all 43 cells the patterning of OB activity was synchronized with the time course of the nasal stimulation. This synchronization was independent of the point in the ongoing respiratory cycle (tracheal breathing) at which the odor stimulation was applied. 3. Patterning of OB single-unit activity was also observed when odor was applied as a series of "inspirations" without intervening expirations. Patterning was observed to follow the time course of the odor stimulation even when this was considerably longer and slower than normal breathing. No patterning of activity was observed during continuous odor stimulation or in the absence of odor stimulation. 4. It is concluded that respiratory patterning of OB single-unit activity in the rat is not directly dependent on centrifugal inputs synchronized to respiration. Rather, the observed pattern of neural activity reflects the phasic stimulation of the olfactory receptors with each inspiration and the dynamics of the circuitry intrinsic to the bulb itself.
Cartwheel and superficial stellate cells of the dorsal cochlear nucleus of mice: intracellular recordings in slices
Authors: Zhang S. , Oertel D.
Published: December 2017

1. Intracellular recordings were made from identified cartwheel and stellate cells in the molecular and fusiform cell layers of the murine dorsal cochlear nucleus (DCN). The aim of the study was to identify and characterize their synaptic inputs and to learn how synaptic inputs and intrinsic electrical properties interact to generate firing patterns. 2. Eight cells labeled by the intracellular injection of biocytin were cartwheel cells. Their axon terminals extended from the deep part of the molecular layer through the fusiform cell layer. Their dendrites extended through the molecular layer and had spines. Both the dendritic and axonal arbors were small, having diameters of approximately 150 microns in the parasagittal plane. 3. When depolarized, cartwheel cells often fired bursts of rapid action potentials superimposed on a slow depolarization. The peaks of action potentials were usually overshooting. Individually occurring action potentials were followed by two afterhyperpolarizations, as in other cells of the DCN. During bursts, action potentials did not have two distinct repolarizing phases. 4. Excitatory postsynaptic potentials (EPSPs) were recorded from cartwheel cells spontaneously and after shocks to the nerve root or to the ventral cochlear nucleus (VCN). The EPSPs rose slowly. When they were suprathreshold they evoked action potentials singly or in bursts. EPSPs evoked by shocks to the nerve root or to the VCN had long latencies, the rise of EPSPs beginning between 5 and 10 ms after the shock. No inhibitory synaptic potentials, either spontaneous or driven with electrical stimulation, were detected in cells whose resting potentials were between -50 and -70 mV. 5. The locations from which excitatory input can be driven electrically are consistent with cartwheel cells receiving excitatory synaptic input from granule cells. 6. One labeled cell was a superficial stellate cell. It had smooth, straight dendrites that radiated parallel to the layers of the DCN; its axonal arbor was also planar and was restricted to the molecular layer. Both the dendritic and axonal arbors of this stellate cell were large, > 500 microns diam in the parasagittal plane. 7. The superficial stellate cell fired trains of action potentials at regular intervals that, like other cells of the DCN, were overshooting and were followed by double undershoots. 8. Shocks to the nerve root and to the surface of the VCN evoked EPSPs after 3.5 and 2 ms, respectively, in the superficial stellate cell. Chemical stimulation of the VCN also evoked excitation. No inhibitory synaptic input, spontaneous or driven, was detected.
Time-varying mechanical behavior of multijointed arm in man
Authors: Lacquaniti F. , Carrozzo M. , Borghese N. A.
Published: December 2017

1. The aim of this study was to describe the time-varying changes in the mechanical parameters of a multijointed limb. The parameters we considered are the coefficients of stiffness, viscosity, and inertia. Continuous pseudorandom perturbations were applied at the elbow joint during a catching task. A modified version of an ensemble technique was used for the identification of time-varying parameters. Torques at the elbow and wrist joints were then modeled with a linear combination of the changes in angular position and velocity weighted by the matrix of angular stiffness and the matrix of angular viscosity, respectively. Control experiments were also performed that involved the stationary maintenance of a given limb posture by resisting actively the applied perturbations. Different limb postures were examined in each such experiment to investigate the dependence of the mechanical parameters on limb geometry. 2. The technique for the identification of limb mechanical parameters proved adequate. The input perturbations applied at the elbow joint elicited angular oscillations at the wrist essentially uncorrelated with those produced at the elbow. The frequency of oscillation is much higher at the wrist than at the elbow, mainly because of the smaller inertia. The variance accounted for by the model was approximately 80% under both stationary and time-varying conditions; in the latter case the value did not vary significantly throughout the task. In addition, the model predicted values of the inertial parameters that were close to the anthropometric measures, and it reproduced the stepwise increase in limb inertia that occurs at the time the ball is held in the hand. 3. The values of angular stiffness and viscosity estimated under stationary conditions did not vary significantly with joint angle, in agreement with previous results obtained under quasi-static postural conditions. The matrix of the coefficients of angular stiffness was not symmetrical, indicating a prominent role for nonautogenic reflex feedbacks with unequal gains for elbow and wrist muscles. 4. A complex temporal modulation of angular stiffness and viscosity was observed during the catching task. The changes in the direct coefficients of angular stiffness tended to covary with those in the coupling coefficients from trial start up to approximately 30 ms before impact time. Around impact time, however, there was a complete dissociation: the direct terms peaked, whereas the coupling terms dropped. The direct terms of angular viscosity also increased before impact, whereas the viscosity coupling terms remained close to zero throughout.(ABSTRACT TRUNCATED AT 400 WORDS)
Long-term dysfunctions of neural stereoscopic mechanisms after unilateral extraocular muscle proprioceptive deafferentation
Authors: Trotter Y. , Celebrini S. , Beaux J. C. , Grandjean B. , Imbert M.
Published: December 2017

1. Neural correlates of the permanent deficits in depth perception that occur when extraocular muscle proprioceptive (EMP) afferents are interrupted unilaterally in kittens were investigated by performing extracellular recordings in the primary visual cortex (area 17) in adulthood. Unilateral section of the ophthalmic branch of the trigeminal nerve (V1 nerve) were performed in 11 cats when they were between 5 and 12 weeks of age (uni-V1 group). Electrophysiological results were compared with those obtained in 17 normal adult cats (control group). 2. Binocular interactions were assessed by testing the sensitivity of cortical neurons to dichoptic presentations of moving sine-wave gratings whose interocular positional phase relationship was randomly varied. The amplitude modulation between the minimum and the maximum binocular responses defined the dynamic range. The degree of binocular suppression or facilitation was assessed by comparing these binocular response limits with the optimal monocular responses evoked through either eye at the best spatial frequency. The variability of both monocular and binocular responses was estimated by using the variation coefficient. 3. In uni-V1 cats, both the dynamic range and the degree of binocular suppression were significantly less pronounced than in controls, whereas binocular facilitation was not affected. The variability of the binocular responses was significantly increased, unlike monocular responses, whose variability was similar to control values. 4. From Fourier analysis of the poststimulus time histograms, two clear-cut categories of cells emerged that were differentially affected in the uni-V1 group. The "modulated" cells showed significantly less binocular suppression than in controls, and the "unmodulated" cells had binocular responses that were significantly more variable than in controls. Results from "simple" cells were similar to those of modulated cells, and results from "complex" cells were similar to those of unmodulated cells. However, in the unmodulated population, which was composed of both simple and complex cells, it was shown that the increase of variability was due to that of complex cells. 5. A nonparametric statistical test was applied on the interocular phase shift tuning curves to determine the minimum stimulus change necessary to elicit a significant change in the neural response. Two categories of cells were determined: the "discriminative" cells (80% in controls but 45% in uni-V1 cats) combined pronounced binocular suppression and dynamic range with relatively low variability. The reverse was true in the case of "nondiscriminative" cells (20% in controls and 55% in uni-V1 cats). 6. In uni-V1 cats, about half of the cells were monocularly activated.(ABSTRACT TRUNCATED AT 400 WORDS)
Vagal afferent stimulation-produced effects on nociception in capsaicin-treated rats
Authors: Ren K. , Zhuo M. , Randich A. , Gebhart G. F.
Published: December 2017

1. The effects of electrical stimulation of cervical vagal afferent fibers on the nociceptive tail-flick (TF) reflex and responses of spinal dorsal horn neurons to noxious cutaneous stimulation were studied in adult rats treated as neonates with either capsaicin or vehicle. 2. Vagal afferent stimulation (VAS) produced biphasic, intensity-dependent effects on the TF reflex in vehicle-treated and untreated control rats. The TF reflex was facilitated in both groups of rats at lesser intensities of VAS (2.5-50 microA) and fully inhibited at greater intensities of VAS (50-100 microA). In contrast, biphasic effects of VAS on the TF reflex generally were not produced in rats treated as neonates with capsaicin. Facilitation of the TF reflex was produced in these rats by lesser intensities of VAS as well as by typically "inhibitory" intensities of VAS; the TF reflex was never inhibited in 6/12 rats, even at the greatest intensity of VAS tested (1,000 microA). When the TF reflex was inhibited by VAS in capsaicin-treated rats, the intensities required were significantly greater than those required in vehicle-treated or untreated rats. 3. In electrophysiological experiments, 77 neurons were recorded in the lumbar spinal dorsal horn of pentobarbital sodium-anesthetized, paralyzed rats treated as neonates with either vehicle or capsaicin. The neurons had receptive fields on the glabrous skin of the plantar surface of the ipsilateral hind foot, and all responded to mechanical stimuli of both nonnoxious and noxious intensities; 16/77 neurons also responded to noxious thermal stimulation. In vehicle-treated rats, nociceptive responses of 50% of 30 units studied were biphasically modulated by VAS, 33% were only inhibited, and 17% were only facilitated by VAS at the intensities tested (5-500 microA). In capsaicin-treated rats, nociceptive responses of 32% of 47 units studied were biphasically modulated by VAS, 15% were only inhibited, and 34% were only facilitated by VAS at the intensities tested (5-500 microA). In addition, nociceptive responses of neurons facilitated at lesser intensities of VAS and not affected at greater intensities of VAS were observed in capsaicin-treated rats (19% of the 47-unit sample). Overall, the proportion of the neuronal sample inhibited by VAS was less, and the proportion of the sample facilitated by VAS was greater in capsaicin-treated rats compared with vehicle-treated rats. 4. The efficacy of the capsaicin treatment was evaluated immunocytochemically.(ABSTRACT TRUNCATED AT 400 WORDS)
Divalent cations block the cyclic nucleotide-gated channel of olfactory receptor neurons
Authors: Zufall F. , Firestein S.
Published: December 2017

1. The effects of external divalent cations on odor-dependent, cyclic AMP-activated single-channel currents from olfactory receptor neurons of the tiger salamander (Ambystoma tigrinum) were studied in inside-out membrane patches taken from dendritic regions of freshly isolated sensory cells. 2. Channels were reversibly activated by 100 microM cyclic AMP. In the absence of divalent cations, the channel had a linear current-voltage relation giving a conductance of 45 pS. With increasing concentrations of either Ca2+ or Mg2+ in the external solution, the channel displayed a rapid flickering behavior. At higher concentrations of divalent cations, the transitions were too rapid to be fully resolved and appeared as a reduction in mean unitary single-channel current amplitude. 3. This effect was voltage dependent, and on analysis was shown to be due to an open channel block by divalent ions. In the case of Mg2+, the block increased steadily with hyperpolarization. In contrast, for Ca2+ the block first increased with hyperpolarization and then decreased with further hyperpolarization beyond -70 mV, providing evidence for Ca2+ permeation of this channel. 4. This block is similar to that seen in voltage-gated calcium channels. Additionally, the cyclic nucleotide-gated channel shows some pharmacological similarities with L-type calcium channels, including a novel block of the cyclic nucleotide channel by nifedipine (50 microM). 5. Our results indicate that the sensory generator current simultaneously depends on the presence of the second messenger and on the membrane potential of the olfactory neuron.
Free nerve ending terminal morphology is fiber type specific for A delta and C fibers innervating rabbit corneal epithelium
Authors: MacIver M. B. , Tanelian D. L.
Published: December 2017

1. A delta and C fibers are the smallest diameter and most numerous axons in peripheral nerve bundles. They have been thought to terminate as "free" nerve endings lacking organized structure. The present study used a vital fluorescent dye to selectively visualize living free nerve endings innervating rabbit corneal epithelium, allowing structure to be correlated with electrophysiological and functional characteristics. 2. Conduction velocity measurement of visually identified nerve endings were used to discriminate between C and A delta fibers. C fiber sensory endings terminated as short (< 50 microns) vertically directed processes clustered within the epithelium. A delta fibers terminated as long (0.1-1.2 mm) horizontal processes running parallel to the epithelial surface. 3. Only A delta fiber endings were mechanoreceptive, and the unique elongated structure imparted directional selectivity. Comparison of physiological and electrical activation indicated that mechanical stimuli were transduced in < 600 microseconds. This study confirms previous suggestions of structural and functional specialization for "free" nerve endings.
Converging influences from visual, auditory, and somatosensory cortices onto output neurons of the superior colliculus
Authors: Wallace M. T. , Meredith M. A. , Stein B. E.
Published: December 2017

1. Physiological methods were used to examine the pattern of inputs from different sensory cortices onto individual superior colliculus neurons. 2. Visual, auditory, and somatosensory influences from anterior ectosylvian sulcus (AES) and visual influences from lateral suprasylvian (LS) cortex were found to converge onto individual multisensory neurons in the cat superior colliculus. An excellent topographic relationship was found between the different sensory cortices and their target neurons in the superior colliculus. 3. Corticotectal inputs were derived solely from unimodal neurons. Multisensory neurons in AES and LS were not antidromically activated from the superior colliculus. 4. Orthodromic and antidromic latencies were consistent with monosynaptic corticotectal inputs arising from LS and the three subdivisions of AES (SIV, Field AES, and AEV). 5. Superior colliculus neurons that received convergent cortical inputs formed a principal component of the tecto-reticulospinal tract. Thus there appears to be extensive cortical control over the output neurons through which the superior colliculus mediates attentive and orientation behaviors. 6. Two other multisensory circuits were identified. A population of multisensory superior colliculus neurons was found, which neither received convergent cortical input nor projected into the tecto-reticulo-spinal tract. In addition, multisensory neurons in AES and LS proved to be independent of the superior colliculus (i.e., they were not corticotectal). While it is likely that these three distinct multisensory neural circuits have different functional roles, their constituent neurons appear to integrate their various sensory inputs in much the same way.
Cultured olfactory interneurons from Limax maximus: optical and electrophysiological studies of transmitter-evoked responses
Authors: Rhines L. D. , Sokolove P. G. , Flores J. , Tank D. W. , Gelperin A.
Published: December 2017

1. The olfactory processing network in the procerebral (PC) lobe of the terrestrial mollusk Limax maximus exhibits a coherent oscillation of local field potential that is modulated by odor input. To understand the cellular basis of this oscillation, we developed a cell culture preparation of isolated PC neurons and studied the responses of isolated cells to stimulation with neurotransmitters known to be present in the PC lobe. 2. The distribution of PC soma diameters suggests at least two different populations of neurons. Approximately 95% of isolated cells had soma diameters of 7-8 microns, with the remaining cells having larger diameters (10-15 microns). 3. Extracellular measurements of action potentials and optical measurements of intracellular calcium concentrations in fura-2-loaded cells were made. Serotonin and dopamine excited PC neurons and promoted transitions from steady to bursty activity. Both amines elicited increases in intracellular calcium, presumably concomitant with the increase in action-potential frequency. 4. Glutamate suppressed action-potential firing and reduced intracellular calcium. This effect was seen most clearly when glutamate was applied to cells excited by high potassium medium. Quisqualate is an effective glutamate agonist in this system, whereas kainate is not. 5. Combined with anatomic and biochemical data and with studies of the effects of these neurotransmitters on the oscillating local field potential of the intact PC network, the data from isolated PC neurons are consistent with the hypothesis that dopamine and serotonin modulate network dynamics, whereas glutamate is involved in generating the basic oscillation of local field potential in the PC. 6. The optical studies of fura-2-loaded cells showed that several treatments that increase the rate of action-potential production lead to elevations in intracellular calcium. Optical studies of intracellular calcium may be useful for multisite measurements of activity in the intact, oscillating PC lobe network.
Serotonin-containing neurons in lobsters: origins and characterization of inhibitory postsynaptic potentials
Authors: Weiger W. A. , Ma P. M.
Published: December 2017

1. The serotonin-containing neurons in the A1 ganglion of the lobster have been shown to act as "gain setters" in neuronal circuits that control the adoption of behaviorally relevant postures. These neurons are subject to tonic inhibition, which has been proposed as an important regulator of their activity. This study explores the pharmacological nature and anatomic location of the neurons responsible for inhibition of these A1 cells; the role played by inhibitory inputs in controlling the firing rates of these neurons is also examined. 2. Three classes of inhibitory postsynaptic potentials (IPSPs) are distinguished in the somata of A1 serotonin-containing neurons. The most common (type I) has amplitudes ranging from 0.4 to 1.5 mV; types II (2-5 mV) and III (< 0.4 mV) are less often seen. 3. Type I IPSPs are reversibly blocked by picrotoxin, a gamma-aminobutyric acid antagonist, but not by serotonin or octopamine antagonists known to act at other lobster synapses. 4. Elimination of type I IPSPs by reversible or irreversible blockage of conduction from the A3 ganglion results in a firing rate increase of approximately 50% in A1 serotonin-containing neurons; IPSP recovery results in a firing rate decrease of corresponding magnitude. Connective transections that do not affect IPSPs do not cause a firing rate increase. 5. Lesions studies suggest that type I IPSPs originate in neurons whose somata are located near the midline of the A3 ganglion; a cell impaled in this region showed action potentials that correlated with IPSPs in an A1 serotonin-containing neuron.
Serotonin-containing neurons in lobsters: the actions of gamma-aminobutyric acid, octopamine, serotonin, and proctolin on activity of a pair of identified neurons in the first abdominal ganglion
Authors: Ma P. M. , Weiger W. A.
Published: December 2017

1. Serotonin has been shown to be an important neurohormone that modulates behavioral output in lobsters. This study explores the neurochemical identity of excitatory and inhibitory inputs to a pair of identified serotonin-containing neurons in the first abdominal ganglion (A1) of the lobster that also contain the pentapeptide proctolin. These neurons are spontaneously active, appear to be driven by an endogenous pacemaking mechanism, and have been shown to play a role in circuits that control behaviorally relevant postures. 2. To explore the exogenous control of neuronal activity, a number of putative neuroactive compounds were superfused over the A1 serotonin-containing neurons in isolated ventral nerve cords. Three amines, gamma-aminobutyric acid (GABA), octopamine, and serotonin, were found to be potent inhibitors in a dose-dependent manner. GABA inhibition had a rapid onset and termination and yielded a transient postinhibitory rebound activity immediately after amine washout; activity eventually returned to the preinhibition level. Octopamine inhibition had a less rapid onset and termination, and the steady-state activity after inhibition was higher than preinhibition firing in most cells (22% of which were statistically significantly increased). Serotonin inhibition had a relatively slow onset and termination, and the steady-state activity after inhibition remained low in most cells (19% significantly decreased). 3. Repeated or prolonged exposure to these three amines reduced the efficacy of inhibition. Three types of desensitization have been empirically defined: 1) rapid desensitization, which tended to dampen the initial inhibition; this was particularly strong for GABA inhibition; 2) low-dose desensitization, in which the A1 serotonin containing neurons became less sensitive to inhibition by a particular concentration of amine after prior exposure to a lower concentration, although the lower concentration may not by itself have had inhibitory effects; this was seen with octopamine inhibition; and 3) long-term desensitization, in which the efficacy of inhibition of a particular amine concentration dwindled with repeated applications (even with up to 160 min washout between applications); this was seen with octopamine and serotonin inhibition, although not for every A1 serotonin-containing neuron analyzed. 4. Bath application of these three amines was still capable of inhibiting the A1 serotonin-containing neurons when inhibitory synaptic transmission was blocked by use of low Ca2+/high Mg2+ solutions. 5. The pentapeptide proctolin excited the A1 serotonin-containing neurons: it activated silent neurons and increased the firing rate of spontaneously active neurons. The excitatory effect outlasted the presence of the peptide.(ABSTRACT TRUNCATED AT 400 WORDS)
Relative contribution of rod and cone inputs to bipolar cells and ganglion cells in the tiger salamander retina
Authors: Hensley S. H. , Yang X. L. , Wu S. M.
Published: December 2017

1. The relative contribution of rod and cone inputs to bipolar and ganglion cells were studied by comparing the response-irradiance relations, spectral sensitivities, and response waveforms of these neurons recorded from the isolated, flat-mounted tiger salamander retina under dark-adapted conditions. 2. Bipolar cells could be differentiated both on the basis of the polarity of the light response and on their relative rod/cone input. Thus some depolarizing bipolar cells appeared more strongly influenced by rod input (DBCR), whereas others were more influenced by cone input (DBCC). Similarly, hyperpolarizing bipolar cells could be divided into those that received rod-dominant input (HBCR) or cone-dominant input (HBCC). 3. The light onset response of sustained-ON ganglion cells reflected both rod-dominant input from DBCRs and cone-dominant input from DBCCs. 4. OFF ganglion cells displayed both a rod-dominant sustained light offset response and a cone-dominant transient light offset response, suggesting input from both HBCRs and HBCCs. 5. In ON-OFF ganglion cells, the light onset response was strongly rod dominated and was presumably mediated by DBCRs, whereas the light offset response displayed both rod and cone influence, suggesting input from HBCRs and HBCCs. The contribution of cones to the light onset response of ON-OFF ganglion cells was only observed in the presence of a rod-adapting background light. 6. A suppression of the light offset responses of OFF and ON-OFF ganglion cells was observed, which was dependent both on the wavelength and irradiance of the light stimulus. 7. These results indicate that the photoreceptor inputs to bipolar cells in the tiger salamander retina are segregated such that they form separate rod-dominant and cone-dominant pathways. Thus the response properties of the different types of ganglion cells are influenced not only by the excitatory and inhibitory inputs they receive from the bipolar and amacrine cells but also whether these inputs are provided through rod-dominant or cone-dominant pathways. The functional implications of these findings are discussed.
Calcium conductances and their role in the firing behavior of neonatal rat hypoglossal motoneurons
Authors: Viana F. , Bayliss D. A. , Berger A. J.
Published: December 2017

1. The role of calcium conductances in action potential generation and repetitive firing behavior of hypoglossal motoneurons (HMs) was investigated using intracellular recording and patch-clamp techniques in a brain stem slice preparation of neonatal rats (0-15 days old). 2. The action potential was followed by an afterdepolarization (ADP). The ADP was voltage dependent, increasing with membrane hyperpolarization. Raising the extracellular Ca2+ concentration or replacing Ca2+ with Ba2+ increased the ADP amplitude, whereas replacement of Ca2+ with Mn2+ blocked it. The ADP was partially reduced by amiloride and low concentrations of Ni2+. 3. The firing behavior of individual neonatal HMs was influenced by membrane potential. From depolarized potentials, HMs fired tonically in response to a depolarizing current pulse, whereas from more hyperpolarized membrane potentials (more negative than -70 mV), a subset of HMs fired an initial burst of action potentials followed by a prolonged afterhyperpolarization and tonic firing. The incidence of burst-firing behavior was highest among young motoneurons and disappeared by the tenth postnatal day. In addition, prominent rebound depolarizations characterized the response of neonatal motoneurons to hyperpolarizing prepulses. 4. Pharmacological characterization of the rebound depolarization demonstrated that it was calcium dependent. Its amplitude was insensitive to tetrodotoxin and it was eliminated by replacement of Ca2+ with Mn2+ or addition of Ni2+. Amiloride (1-1.5 mM) had no effect on the rebound response or burst firing. 5. The presence of high-threshold calcium spikes was detected at all postnatal ages, but only after blockade of outward currents with intra- or extracellular tetraethylammonium. The high-threshold calcium spikes were greatly enhanced when Ba2+ replaced Ca2+. 6. Calcium currents of neonatal HMs were characterized in whole-cell patch-clamp recordings of thin medullary slices under conditions that minimized voltage-dependent Na+ and K+ currents. Low voltage-activated (LVA) and a high voltage-activated (HVA) calcium current components were identified on the basis of their voltage thresholds for activation, kinetics of inactivation, and pharmacological sensitivity. 7. The LVA calcium current began to activate at around -60 mV and inactivated nearly completely within 100 ms. Complete steady-state inactivation occurred at potentials more positive than -60 mV. The LVA current was selectively reduced by 1 mM amiloride (31%). 8. A larger-amplitude calcium current activated at potentials around -35 mV. Inactivation of this HVA current was slower than that of the LVA current and incomplete. About 1/3 of this current was sensitive to 1 microM omega-conotoxin GVIA, whereas a smaller fraction was blocked by 10 microM nifedipine.(ABSTRACT TRUNCATED AT 400 WORDS)
Transient enhancement of low-threshold calcium current in thalamic relay neurons after corticectomy
Authors: Chung J. M. , Huguenard J. R. , Prince D. A.
Published: December 2017

1. The alterations of voltage-sensitive calcium currents produced in thalamic cells by injury were investigated under voltage clamp using patch-clamp recordings in the whole-cell configuration. 2. One day after unilateral cortical ablation in immature rats (postnatal day 7), low-threshold transient calcium (T) currents in acutely isolated thalamic relay neurons (RNs) were increased by 68% compared with contralateral controls (P < 0.001). Three days after the operation, T currents in injured neurons were at 44% of control levels (P < 0.001). On the other hand, high-threshold (L) calcium currents in RNs did not change over the same interval. 3. To investigate the mechanism for the increase of T current, both kinetics and voltage dependency of activation and inactivation were examined. At a test voltage of -40 mV, the activation time constant decreased from 4.1 to 3.2 ms (P < 0.05); however, this small change was insufficient to explain the large increase in T current. Time constants for both fast and slow inactivation did not change significantly, nor did voltage dependence of activation or inactivation of thalamic T currents. 4. Methyl-phenyl-succinimide (MPS, 1 mM), a compound known to block T currents, was used to examine possible alterations in the pharmacological properties of T channels after injury. MPS was more effective in reducing T currents in normal versus injured RNs (24 and 20% reductions, respectively; P < 0.05), suggesting that pharmacological properties of T channels in the injured RNs may be different from those of the normal RNs.(ABSTRACT TRUNCATED AT 250 WORDS)
Intrinsic properties and evoked responses of guinea pig subicular neurons in vitro
Authors: Stewart M. , Wong R. K.
Published: December 2017

1. Intracellular recordings were used to examine the membrane properties and evoked responses of subicular neurons in horizontal and parasagittal slices from guinea pig brain as a step toward understanding excitatory transmission through the hippocampus. 2. Most cells (49/74) could fire a burst discharge, a portion of which was Ca2+ dependent, in response to direct depolarization or in response to orthodromic or antidromic activation. Other cells (23/74) could not be made to burst, but instead fired single repetitive spikes when directly depolarized or single spikes in response to orthodromic or antidromic activation. Two recorded cells appeared to be interneurons and differed from bursting and non-bursting cells in action-potential shape and response to extracellular stimulation. 3. Bursting cells differed from nonbursting cells in their membrane properties: 1) their time constants were typically shorter (averaging 7.4 ms for bursting cells and 11.5 ms for nonbursting cells), 2) they exhibited a pronounced "sag" in the potential response to hyperpolarizing current injection, and 3) they responded at the break of a hyperpolarizing stimulus with a depolarization (anodal break potential). The sag and the anodal break potential were not detected in recordings from nonbursting neurons. 4. A single-spiking mode could be induced in bursting cells by depolarization from resting potential to about -60 mV. Conversely, hyperpolarization of nonbursting cells did not convert them to bursting cells. 5. Both bursting and nonbursting cell types could be antidromically driven. Whereas both excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) were prominent in nonbursting cells, IPSPs were observed at a lower stimulus intensities than EPSPs in most cells. EPSPs were evident in bursting cells and they triggered burst discharges. IPSPs in bursting cells were detected only when these cells were depolarized, eliminating burst responses. 6. Spontaneous firing rates were low (averaging < 1 spike/s) for both cell types. Addition of picrotoxin produced spontaneous burst or EPSP responses in bursting cells, synchronous with different patterns of picrotoxin-induced population bursts originating in CA3 and/or entorhinal cortex. Individual subicular cells followed CA3 or entorhinal cortex or both. No such activity was recorded in nonbursting cells. No increases in activity in either cell type were seen after picrotoxin application to isolated pieces of subicular cortex.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of bilateral and unilateral ablation of auditory cortex in cats on the unconditioned head orienting response to acoustic stimuli
Authors: Beitel R. E. , Kaas J. H.
Published: December 2017

1. Reflexive head orienting responses (ORs) elicited by bursts of wide-band noise were investigated in cats after bilateral or unilateral ablation of the auditory cortex, and the cats' performance was compared with that of control cats. The OR was used as an indication of ability to orient toward the azimuthal direction of a source of sound. 2. To adequately test this ability, a unique combination of stimulus duration and position of the sound source was selected on each trial. Stimulus durations (0.1, 0.3, and 1.5 s) were selected so that the offset of a burst of noise occurred before, during, or after an OR. The stimuli were produced from speakers positioned approximately at the interaural horizontal plane within each quadrant of a cat's auditory field. The ORs were recorded on moving film and analyzed quantitatively. 3. In the control cats, the trajectory of the OR was characterized by a saccadic profile (rapid steplike movement, monophasic velocity, and biphasic acceleration). The accuracy of the OR varied directly with stimulus duration, suggesting that the response was modified by auditory feedback produced by a head movement during the stimulus. Corrective responses executed during long-duration (1.5 s) stimuli reduced residual mean error to < 7 degrees in each of the control animals. The mean error in orientation was smaller for sources located in the frontal sound field than for sources located behind the coronal plane the head (> 90 degrees). When brief (0.1 s) stimuli were presented behind the head, the cats confused back with front directions on most of the trials. 4. Compared with performance in the control cats, bilateral destruction of the auditory geniculocortical system severely impaired a cat's ability to orient consistently and accurately toward a source of sound. Latencies to the onset of ORs were increased, the magnitudes of ORs were reduced, average error in orienting to a sound source was larger under every stimulus duration-source position combination, relatively few corrective responses were executed, and residual mean error was significantly elevated (bilateral = 28.1 degrees; control = 3.1 degrees). Several animals with bilateral lesions also made vertical errors in orienting to azimuthal sources of sound. 5. However, in the bilateral lesion group, ORs were initiated in the correct right or left direction; and, rather than eliminating accurate responses altogether, the lesions reduced the probability of their occurrence. Furthermore, the saccadic profile of the response was preserved, providing evidence that the motor control system for the OR was not perturbed by the bilateral lesions.(ABSTRACT TRUNCATED AT 400 WORDS)
Cochlear nerve fiber responses to amplitude-modulated stimuli: variations with spontaneous rate and other response characteristics
Authors: Cooper N. P. , Robertson D. , Yates G. K.
Published: December 2017

1. Single-fiber responses to sinusoidally amplitude-modulated (AM) tones were recorded from the cochlear nerves of anesthetized guinea pigs. Stimuli were presented at the fiber's characteristic frequency (CF) and covered the intensity range between the fiber's minimum rate threshold and 90-100 dB SPL in 5- or 6-dB steps. The amount of modulation in each fiber's response and the average rate of the responses were quantified. The observed response modulation was compared with the modulation to be expected on the assumption that the instantaneous discharge rates varied with intensity in the same way that the average rates did (i.e., as predicted from each fiber's average-rate vs. level function). 2. The difference between the observed and expected response modulation varied widely across fibers. In most fibers' the responses to a limited range of stimulus intensities (typically between 20 and 30 dB above the fiber's rate threshold) were modulated far more than expected on the basis of their average rates, with responses to stimuli either above or below this range differing progressively less from expectation. Little or no response modulation was observed above approximately 70 dB SPL in these fibers. Other fibers exhibited response modulation that exceeded the expected modulation by smaller amounts, but maintained this modulation to much higher sound pressure levels. 3. The discrepancy between the observed and expected responses to AM stimuli also varied with the frequency of modulation (fm) within individual fibers. The discrepancies were least pronounced at low fms (e.g., 10 Hz) but became progressively larger as fm was increased to between 50 and 320 Hz (subject to the inter-fiber variations described in 2, above). 4. The AM response characteristics varied systematically with the fiber's spontaneous rate and other response characteristics (e.g., rate threshold, CF rate vs. level function type, and rapid adaptation characteristics). In particular, the most sensitive, high spontaneous rate fibers had responses that adapted rapidly after the onset of a stimulus, and showed the greatest enhancement of AM-related information at low-to-moderate stimulus intensities. However, these fibers appeared incapable of encoding AM-related information at high intensities, since their response rates "saturated" and their AM response enhancements diminished around 30 dB above threshold. In contrast, the less sensitive (i.e., higher threshold), lower spontaneous rate fibers showed less evidence of rapid adaptation near the onsets of their response, and lesser enhancements of the modulated responses predicted from their average-rate versus level functions.(ABSTRACT TRUNCATED AT 400 WORDS)
Voltage-gated potassium currents in acutely dissociated rat cortical neurons
Authors: Foehring R. C. , Surmeier D. J.
Published: December 2017

1. We describe three outward K+ current components in acutely dissociated neurons from rat sensorimotor cortex on the basis of inactivation kinetics and voltage dependence. 2. The fast A current (IAf) was completely inactivated at -40 mV and half-inactivated at -52 mV. It activated [time to peak (TTP) 8 ms at -10 mV] and was inactivated (tau inact = 12 ms at -10 mV) rapidly. Recovery from inactivation had a time constant of approximately 80 ms at -100 mV. It was insensitive to tetraethyl ammonium (TEA) and dendrotoxin but was blocked by 4-aminopyridine (4-AP, IC50 = 1 mM). 3. The slowly inactivating current (IKS) was the largest current seen in acutely dissociated adult neurons. It was completely inactivated at -40 mV, half-inactivated at -98 mV, and was kinetically slower (TTP = 130 ms at -10 mV; tau inact = 293 ms at -10 mV) than the fast A current. Deactivation tails were fit with the sum of two exponentials with time constants of 2-10 and 15-40 ms. IKS recovered from inactivation with a time constant of approximately 1,200 ms at -100 mV. 4. There were two components that inactivated with even slower kinetics. The very slowly inactivating current (IKSS) was operationally defined as the current remaining after a 5-s hold at -40 mV. One component inactivated with a time constant of 1,927 ms at -10 mV. The other component showed no inactivation over a 5-s test command, but in 40- to 50-s steps to -10 mV, inactivated with a tau of approximately 20 s. The very slowly inactivating current activated with similar kinetics to IKS (TTP = 121 ms at -10 mV), and two deactivation tails, with kinetics similar to those after the -100 mV prepulse, were observed after holding at -40 mV. 5. Both IKS and IKSS were sensitive to TEA. Seventy-six percent (76%) of IKSS was blocked by 30 mM TEA. Two components to the TEA block were present for IKSS, with IC50s of 88 microM (67% of blockable current) and 7 mM (33%). Seventy percent (70%) of IKS was blocked by 30 mM TEA. For the IKS current, there were also two effective concentrations, with IC50s of 8 microM (21% of blockade current) and 3 mM (79%). 6. IKS and IKSS were also sensitive to 4-AP. Seventy-six percent (76%) of IKSS was blocked by 3-5 mM 4-AP. IKSS exhibited two components of 4-AP block.(ABSTRACT TRUNCATED AT 400 WORDS)
Differential modulation of voltage-dependent currents in Hermissenda type B photoreceptors by serotonin
Authors: Acosta-Urquidi J. , Crow T.
Published: December 2017

1. In identified photoreceptors in the eyes of Hermissenda, serotonin (5-HT) enhances the peak and plateau phases of light-evoked generator potentials and modulates light-dependent and voltage-dependent currents. In addition, electrophysiological and morphological studies indicate that 5-HT may contribute to cellular plasticity detected in the visual system of Hermissenda produced by classical conditioning procedures. With the use of conventional two-electrode voltage-clamp techniques, we examined the effects of 5-HT on three distinct currents recorded across the soma membranes of identified lateral and medial type B photoreceptors in the isolated circumesophageal nervous system. 2. The inward rectifier (Iir), a putative K(+)-dependent conductance, activates in 0-Na artificial seawater at membrane potentials greater than -60 mV, is voltage dependent, noninactivating, and reaches steady-state within 800 ms to 3 s at -100 mV. Bath application of 10(-4) M 5-HT consistently enhanced the magnitude of Iir at all potentials tested (-60 to -100 mV) and, in some cases, allowed expression of Iir, which was not initially detectable before the application of 5-HT. 3. The major component of outward K+ current in type B photoreceptors with IA and IK(Ca) blocked is the delayed rectifier [IK(v)]. 5-HT (10(-4) M) produced both an increase as well as a decrease in the peak amplitude of IK(v) and consistently slowed its inactivation rate and reduced twin-pulse inactivation. 4. A previously identified outward K+ current in type B photoreceptors has properties that are similar to the A current (IA).(ABSTRACT TRUNCATED AT 250 WORDS)