bluuebunny/crossref_metadata_2025 huggingface dataset:
Synaptically Evoked Dendritic Action Potentials in Rat Neocortical Pyramidal Neurons
Authors: Schwindt Peter C. , Crill Wayne E.
Published: December 2017

Schwindt, Peter C. and Wayne E. Crill. Synaptically evoked dendritic action potentials in rat neocortical pyramidal neurons. J. Neurophysiol. 79: 2432–2446, 1998. In a previous study iontophoresis of glutamate on the apical dendrite of layer 5 pyramidal neurons from rat neocortex was used to identify sites at which dendritic depolarization evoked small, prolonged Ca2+ spikes and/or low-threshold Na+ spikes recorded by an intracellular microelectrode in the soma. These spikes were identified as originating in the dendrite. Here we evoke similar dendritic responses by electrical stimulation of presynaptic elements near the tip of the iontophoretic electrode with the use of a second extracellular electrode. In 9 of 12 recorded cells, electrically evoked excitatory postsynaptic potentials (EPSPs) above a minimum size triggered all-or-none postsynaptic responses similar to those evoked by dendritic glutamate iontophoresis at the same site. Both the synaptically evoked and the iontophoretically evoked depolarizations were abolished reversably by blockade of glutamate receptors. In all recorded cells, the combination of iontophoresis and an EPSP, each of which was subthreshold for the dendritic spike when given alone, evoked a dendritic spike similar to that evoked by a sufficiently large iontophoresis. In one cell tested, dendritic spikes could be evoked by the summation of two independent subthreshold EPSPs evoked by stimulation at two different locations. We conclude that the dendritic spikes are not unique to the use of glutamate iontophoresis because similar spikes can be evoked by EPSPs. We discuss the implications of these results for synaptic integration and for the interpretation of recorded synaptic potentials.
Complex Synaptic Current Waveforms Evoked in Hippocampal Pyramidal Neurons by Extracellular Stimulation of Dentate Gyrus
Authors: Xiang Zixiu , Brown Thomas H.
Published: December 2017

Xiang, Zixiu and Thomas H. Brown. Complex synaptic current waveforms evoked in hippocampal pyramidal neurons by extracellular stimulation of dentate gyrus. J. Neurophysiol. 79: 2475–2484, 1998. Excitatory postsynaptic currents (EPSCs) evoked in hippocampal CA3 pyramidal neurons by extracellular stimulation of the dentate gyrus typically exhibit complex waveforms. They commonly have inflections or notches on the rising phase; the decay phase may exhibit notches or other obvious departures from a simple monoexponential decline; they often display considerable variability in the latency from stimulation to the peak current; and the rise times tend to be long. One hypothesis is that these complex EPSC waveforms might result from excitation via other CA3 pyramidal cells that were recruited antidromically or trans-synaptically by the stimulus due to the complex anatomy of this region. An alternative hypothesis is that EPSC complexity does not emerge from the functional anatomy but rather reflects an unusual physiological property, intrinsic to excitation-secretion coupling in mossy-fiber (mf) synaptic terminals, that causes asynchronous quantal release. We evaluated certain predictions of our anatomic hypothesis by adding a pharmacological agent to the normal bathing medium that should suppress di- or polysynaptic responses. For this purpose we used baclofen (3 μM), a selective agonist for the γ-aminobutyric acid B receptor. The idea was that baclophen should discriminate against polysynaptic versus monosynaptic inputs by hyperpolarizing the cells, bringing them further from spike threshold and possibly also through inhibitory presynaptic actions. Whole cell recordings were done from visually preselected CA3 pyramidal neurons and EPSCs were evoked by fine bipolar electrodes positioned into the granule cell layer of the dentate. To the extent that the EPSC complexity reflects di- or polysynaptic responses, we predicted baclofen to reduce the number of notches on the rising and decay phases, reduce the variance in latency to peak of the EPSCs, decrease the amplitudes and rise times of the individual and averaged EPSCs, and increase the apparent failures in evoked EPSCs. All of these predictions were confirmed, in support of the hypothesis that these complex EPSC waveforms commonly reflect di- or polysynaptic responses. We also documented a distinctly different, intermittent, form of EPSC complexity, which also is predicted and easily explained by our anatomic hypothesis. In particular, the results were in accord with the suggestion that stimulation of the dentate gyrus might antidromically stimulate axon collaterals of CA3 neurons that make recurrent synapses onto the recorded cell. We conclude that the overall pattern of results is consistent with expectations based on the functional anatomy. The explanation does not demand a special type of intrinsic asynchronous mechanism for excitation-secretion coupling in the mf synapses.
Effects of Quinine on the Excitability and Voltage-Dependent Currents of Isolated Spiral Ganglion Neurons in Culture
Authors: Lin Xi , Chen Shanping , Tee Daniel
Published: December 2017

Lin, Xi, Shanping Chen, and Daniel Tee. Effects of quinine on the excitability and voltage-dependent currents of isolated spiral ganglion neurons in culture. J. Neurophysiol. 79: 2503–2512, 1998. This work examined how quinine, a drug that induces both hearing loss and tinnitus, interfered with the excitability of spiral ganglion (SG) neurons in cultures. The membrane potential changes and the modification of the action-potential waveform induced by quinine were studied in SG neurons under current clamp. The effects of the drug on voltage-dependent currents in SG neurons were also investigated by the voltage-clamp method. Quinine did not appreciably affect either resting membrane potentials or input resistance at rest. However, action potentials fired by SG neurons were significantly broadened by the presence of quinine. With higher concentrations of quinine (>20 μM), the amplitude of action potentials was also reduced. Voltage-clamp results demonstrated that quinine primarily blocked the whole cell potassium currents ( IK) in a voltage-dependent manner. Up to 100 μM of quinine did not appreciably block IKevoked by a test pulse to −35 mV. In contrast, IKwas significantly reduced with more positive test pulses, e.g., the concentration needed to obtain 50% inhibition (IC50) was 8 μM for a test pulse to 65 mV. At higher concentrations (>20 μM), quinine also reduced the size of sodium currents ( INa) in a use-dependent manner, while leaving calcium currents ( ICa) relatively unaffected. Compared with the potency of quinine's effects on other targets in the inner ear, the relatively low IC50and the voltage-dependent nature of quinine inhibition on IKsuggested that its modulation of the waveform and threshold of action potentials of SG neurons probably was primarily responsible for its ototoxic effects. From the point of view of how neural signaling process is affected by the drug, quinine-induced tinnitus may be explained by its broadening of action potentials while the drug's inhibition on INamay result in hearing loss by making the conversion from excitatory postsynaptic potentials to the generation of action potentials more difficult.
Dopamine Receptor–Mediated Mechanisms Involved in the Expression of Learned Activity of Primate Striatal Neurons
Authors: Watanabe Katsushige , Kimura Minoru
Published: December 2017

Watanabe, Katsushige and Minoru Kimura. Dopamine receptor–mediated mechanisms involved in the expression of learned activity of primate striatal neurons. J. Neurophysiol. 79: 2568–2580, 1998. To understand the mechanisms by which basal ganglia neurons express acquired activities during and after behavioral learning, selective dopamine (DA) receptor antagonists were applied while recording the activity of striatal neurons in monkeys performing behavioral tasks. In experiment 1, a monkey was trained to associate a click sound with a drop of reward water. DA receptor antagonists were administered by micropressure using a stainless steel injection cannula (300 μm ID) through which a Teflon-coated tungsten wire for recording neuronal activity had been threaded. Responses to sound by tonically active neurons (TANs), a class of neurons in the primate striatum, were recorded through a tungsten wire electrode during the application of either D1- or D2-class DA receptor antagonists (total volume <1 μl, at a rate of 1 μl/5–10 min). Application of the D2-class antagonist, (−)-sulpiride (20 μg/μl, 58 mM, pH 6.8), abolished the responses of four of five TANs examined. In another five TANs, neither the D2-class antagonist nor the D1-class antagonists, SCH23390 (10 μg/μl, 31 mM, pH 5.7) or cis-flupenthixol (30 μg/μl, 59 mM, pH 6.6) significantly suppressed responses. In experiment 2, four- or five-barreled glass microelectrodes were inserted into the striatum. The central barrel was used for extracellular recording of activity of TANs. Each DA receptor antagonist was iontophoretically applied through one of the surrounding barrels. SCH23390 (10 mM, pH 4.5) and (−)-sulpiride (10 mM, pH 4.5) were used. The effects of iontophoresis of both D1- and D2-class antagonists were examined in 40 TANs. Of 40 TANs from which recordings were made, responses were suppressed exclusively by the D2-class antagonist in 19 TANs, exclusively by the D1-class antagonist in 3 TANs, and by both D1- and D2-class antagonists in 7 TANs. When 0.9% NaCl, saline, was applied by pressure (<1 μl) or by iontophoresis (<30 nA) as a control, neither the background discharge rates nor the responses of TANs were significantly influenced. Background discharge rate of TANs was also not affected by D1- or D2-class antagonists applied by either micropressure injection or iontophoresis. It was concluded that the nigrostriatal DA system enables TANs to express learned activity primarily through D2-class and partly through D1-class receptor–mediated mechanisms in the striatum.
Caudal Pontine Reticular Formation of C57BL/6J Mice: Responses to Startle Stimuli, Inhibition by Tones, and Plasticity
Authors: Carlson Stephanie , Willott James F.
Published: December 2017

Carlson, Stephanie and James F. Willott. Caudal pontine reticular formation of C57BL/6J mice: responses to startle stimuli, inhibition by tones, and plasticity. J. Neurophysiol. 79: 2603–2614, 1998. C57BL/6J (C57) mice were used to examine relationships between the behavioral acoustic startle response (ASR) and the responses of neurons in the caudal pontine reticular formation (PnC) in three contexts: 1) responses evoked by basic startle stimuli; 2) the prepulse inhibition (PPI) paradigm; and 3) the effects of high-frequency hearing loss and concomitant neural plasticity that occurs in middle-aged C57 mice. 1) Responses (evoked action potentials) of PnC neurons closely paralleled the ASR with respect to latency, threshold, and responses to rapidly presented stimuli. 2) “Neural PPI” (inhibition of responses evoked by a startle stimulus when preceded by a tone prepulse) was observed in all PnC neurons studied. 3) In PnC neurons of 6-mo-old mice with high-frequency (>20 kHz) hearing loss, neural PPI was enhanced with 12- and 4-kHz prepulses, as it is behaviorally. These are frequencies that have become “overrepresented” in the central auditory system of 6-mo-old C57 mice. Thus neural plasticity in the auditory system, induced by high-frequency hearing loss, is correlated with increased salience of the inhibiting tones in both behavioral and neural PPI paradigms.
Extracellular K+ Induces Locomotor-Like Patterns in the Rat Spinal Cord In Vitro: Comparison With NMDA or 5-HT Induced Activity
Authors: Bracci E. , Beato M. , Nistri A.
Published: December 2017

Bracci, E., M. Beato, and A. Nistri. Extracellular K+ induces locomotor-like patterns in the rat spinal cord in vitro: comparison with NMDA or 5-HT induced activity. J. Neurophysiol. 79: 2643–2652, 1998. Bath-application of increasing concentrations of extracellular K+ elicited alternating motor patterns recorded from pairs of various lumbar ventral roots of the neonatal rat (0–2 days old) spinal cord in vitro. The threshold concentration of K+ for this effect was 7.9 ± 0.8 mM (mean ± SD). The suprathreshold concentration range useful to evoke persistent motor patterns (lasting ≥10 min) was very narrow (∼1 mM) as further increments elicited only rhythmic activity lasting from 20 s to a few minutes. On average, the fastest period of rhythmic patterns was 1.1 ± 0.3 s. Intracellular recording from lumbar motoneurons showed that raised extracellular K+ elicited membrane potential oscillations with superimposed repetitive firing. In the presence of N-methyl-d-aspartate (NMDA) or non-NMDA receptor blockers [ R(−)-2-amino-phosphonovaleric acid or 6-cyano-7-nitroquinoxaline-2,3-dione, respectively] extracellular K+ increases could still induce motor patterns although the threshold concentration was raised. Serotonin (5-HT) also induced alternating motor patterns (threshold 15 ± 7 μM) that were consistently slower than those induced by high K+ or NMDA. Ritanserin (1 μM) prevented the locomotor-like activity of 5-HT but not that of high K+ provided the concentration of the latter was further increased. Subthreshold concentrations of K+ became effective in the presence of subthreshold doses of 5-HT or NMDA, indicating mutual facilitation between these substances. The fastest pattern frequency was observed by raising K+ or by adding NMDA. In the presence of 5-HT, the pattern frequency was never as fast even if NMDA (or high K+) was coapplied. Furthermore, application of 5-HT significantly slowed down the K+- or NMDA-induced rhythm, an effect strongly potentiated in the presence of ritanserin. It is suggested that the operation of the spinal locomotor network was activated by rises in extracellular K+, which presumably led to a broad increase in neuronal excitability. Whenever the efficiency of excitatory synaptic transmission was diminished (for example by glutamate receptor antagonism), a larger concentration of K+ was required to evoke locomotor-like patterns. The complex effect (comprising stimulation and inhibition) of 5-HT on alternating pattern generation appeared to result from a dual action of this substance on the spinal locomotor network.
Modeling Control of Eye Orientation in Three Dimensions. I. Role of Muscle Pulleys in Determining Saccadic Trajectory
Authors: Raphan Theodore
Published: December 2017

Raphan, Theodore. Modeling control of eye orientation in three dimensions. I. Role of muscle pulleys in determining saccadic trajectory. J. Neurophysiol. 79: 2653–2667, 1998. This study evaluates the effects of muscle axis shifts on the performance of a vector velocity-position integrator in the CNS. Earlier models of the oculomotor plant assumed that the muscle axes remained fixed relative to the head as the eye rotated into secondary and tertiary eye positions. Under this assumption, the vector integrator model generates torsional transients as the eye moves from secondary to tertiary positions of fixation. The torsional transient represents an eye movement response to a spatial mismatch between the torque axes that remain fixed in the head and the displacement plane that changes by half the angle of the change in eye orientation. When muscle axis shifts were incorporated into the model, the torque axes were closer to the displacement plane at each eye orientation throughout the trajectory, and torsional transients were reduced dramatically. Their size and dynamics were close to reported data. It was also shown that when the muscle torque axes were rotated by 50% of the eye rotation, there was no torsional transient and Listing's law was perfectly obeyed. When muscle torque axes rotated >50%, torsional transients reversed direction compared with what occurred for muscle axis shifts of <50%. The model indicates that Listing's law is implemented by the oculomotor plant subject to a two-dimensional command signal that is confined to the pitch-yaw plane, having zero torsion. Saccades that bring the eye to orientations outside Listing's plane could easily be corrected by a roll pulse that resets the roll state of the velocity-position integrator to zero. This would be a simple implementation of the corrective controller suggested by Van Opstal and colleagues. The model further indicates that muscle axis shifts together with the torque orientation relationship for tissue surrounding the eye and Newton's laws of motion form a sufficient plant model to explain saccadic trajectories and periods of fixation when driven by a vector command confined to the pitch-yaw plane. This implies that the velocity-position integrator is probably realized as a subtractive feedback vector integrator and not as a quaternion-based integrator that implements kinematic transformations to orient the eye.
Cellular Mechanisms Underlying Intrathalamic Augmenting Responses of Reticular and Relay Neurons
Authors: Timofeev Igor , Steriade Mircea
Published: December 2017

Timofeev, Igor and Mircea Steriade. Cellular mechanisms underlying intrathalamic augmenting responses of reticular and relay neurons. J. Neurophysiol. 79: 2716–2729, 1998. Augmenting (or incremental) responses are progressively growing potentials elicited by 5- to 15-Hz stimulation within the thalamus, cerebral cortex, or by setting into action reciprocal thalamocortical neuronal loops. These responses are associated with short-term plasticity processes in thalamic and cortical neurons. In the present study, in vivo intracellular recordings of thalamic reticular (RE) and thalamocortical (TC), as well as dual intracellular recordings, were used to explore the mechanisms of two types of intrathalamic augmenting responses elicited by thalamic stimuli at 10 Hz in decorticated cats. As recently described, after decortication, TC cells display incremental burst responses to thalamic stimuli that occur through either progressive depolarization (high threshold, HT) or progressive hyperpolarization leading to deinactivation of low-threshold (LT) spike bursts. Here, low-intensity stimuli (10 Hz) to dorsal thalamic nuclei elicited decremental responses in GABAergic RE cells, consisting of a progressive diminution in the number of action potentials in successive spike bursts, whereas higher stimulation (>50% of maximal strength) induced augmentation characterized by an increased number of spikes in repetitive responses. These opposing discharge patterns occurred in the absence of changes in the membrane potential of RE cells. In TC cells, augmentation depended on the thalamic site where testing volleys were applied. With stimuli applied closer to the site of impalement, augmenting resulted from a transformation from LT spike bursts into HT responses. Augmenting responses were followed by self-sustained oscillatory activity, within the frequency of spindles (7–14 Hz) or clock-like delta oscillation (1–4 Hz). As LT augmentation in TC cells results from their progressive hyperpolarization, we tested the effects exerted by the activating depolarizing system arising in the mesopontine cholinergic nuclei and found that such conditioning pulse-trains prevented the hyperpolarizing-rebound sequences as well as the LT augmenting in TC cells. We propose that the depolarization-dependent (HT) augmenting responses in TC cells result from decremental responses in RE neurons that are due to intra-RE inhibitory processes leading to disinhibition in target TC neurons, whereas LT-type augmenting in TC cells is produced mainly by incremental responses in GABAergic RE neurons.
Ionic Basis for Serotonin-Induced Bistable Membrane Properties in Guinea Pig Trigeminal Motoneurons
Authors: Hsiao Chie-Fang , Negro Christopher A. Del , Trueblood Peggy R. , Chandler Scott H.
Published: December 2017

Hsiao, Chie-Fang, Christopher A. Del Negro, Peggy R. Trueblood, and Scott H. Chandler. Ionic basis for serotonin-induced bistable membrane properties in guinea pig trigeminal motoneurons. J. Neurophysiol. 79: 2847–2856, 1998. Intracellular recordings and pharmacological manipulations were employed to investigate the ionic basis for serotonin-induced bistable membrane behaviors in guinea pig trigeminal motoneurons (TMNs). In voltage clamp, 10 μM serotonin (5-HT) induced a region of negative slope resistance (NSR) in the steady-state current-voltage ( I-V) relationship at potentials less negative than −58 mV, creating the necessary conditions for membrane bistability. The contributions of sustained Na+ and Ca2+ currents to the generation of the NSR were investigated using specific ion channel antagonists and agonists. The NSR was eliminated by the L-type Ca2+ channel antagonist nifedipine (5–10 μM), indicating the contribution of L channels. In nifedipine, inward rectification was present in the I-V relationship in a similar voltage range (greater than −58 mV). This region was subsequently linearized by tetrodotoxin (TTX), indicating the presence of a persistent Na+ current. When the 5-HT–induced NSR was eliminated by perfusion in low Ca2+ solution (0.4 mM), it was restored by the Na+ channel agonist veratridine (10 μM). Commensurate with bistability, in current clamp during bath application of 5-HT, plateau potentials were elicited by transient depolarizing or hyperpolarizing stimuli. Plateau potentials evoked by depolarization were observed under control and TTX conditions, but were blocked by nifedipine, suggesting the participation of an L-type Ca2+ current. Plateau potentials initiated after release from hyperpolarization (anode break) were blocked by 300 μM Ni2+, suggesting the responses relied on deinactivation of a T-type Ca2+ current. Conditional bursting was also observed in 5-HT. Nifedipine or low Ca2+ solutions blocked bursting, and the L-channel agonist Bay K 8644 (10 μM) extended the duration of individual bursts, demonstrating the role of L-type Ca2+ currents. Interestingly, when bursting was blocked by nifedipine or low Ca2+, it could be restored by veratridine application via enhancement of the persistent Na+ current. We conclude that bistable membrane behaviors in TMNs are mediated by L-type Ca2+ and persistent Na+ currents. 5-HT is associated with enhancement of TMN activity during oral-motor activity; the induction of bistable membrane properties by 5-HT represents a cellular mechanism for this enhancement.
Differential Regulation of Synaptic Inputs to Dentate Hilar Border Interneurons by Metabotropic Glutamate Receptors
Authors: Doherty James , Dingledine Raymond
Published: December 2017

Doherty, James and Raymond Dingledine. Differential regulation of synaptic inputs to dentate hilar border interneurons by metabotropic glutamate receptors. J. Neurophysiol. 79: 2903–2910, 1998. Regulation of synaptic transmission by metabotropic glutamate receptors (mGluRs) was examined at two excitatory inputs to interneurons with cell bodies at the granule cell–hilus border in hippocampal slices taken from neonatal rats. Subgroup-selective mGluR agonists altered the reliability, or probability of transmitter release, of evoked minimal excitatory synaptic inputs and decreased the amplitudes of excitatory postsynaptic currents (EPSCs) evoked with conventional stimulation. The group II–selective agonist, (2S,1R′,2R′,3R′)-2-(2,3-dicarboxylcyclopropyl) glycine (DCG-IV; 1 μM), reversibly depressed the reliability of EPSCs evoked by stimulation of the dentate granule cell layer. However, DCG-IV had no significant effect on EPSCs evoked by CA3 stimulation in the majority (82%) of hilar border interneurons. Both the group III–selective agonist, l-(+)-2-amino-4-phosphonobutyric acid (l-AP4; 3 μM), and the group I–selective agonist, (RS)-3,5-dihydroxyphenylglycine (DHPG; 20 μM) reversibly depressed synaptic input to interneurons from both CA3 and the granule cell layer. We conclude that multiple pharmacologically distinct mGluRs presynaptically regulate synaptic transmission at two excitatory inputs to hilar border interneurons. Further, the degree of mGluR-meditated depression of excitatory drive is greater at synapses from dentate granule cells onto interneurons than at synapses from CA3 pyramidal cells.
Synaptically Evoked Glutamate Transport Currents May Be Used To Detect the Expression of Long-Term Potentiation in Cerebellar Culture
Authors: Linden David J.
Published: December 2017

Linden, David J. Synaptically evoked glutamate transport currents may be used to detect the expression of long-term potentiation in cerebellar culture. J. Neurophysiol. 79: 3151–3156, 1998. Cerebellar long-term potentiation (LTP) is a use-dependent increase in the strength of the granule cell-Purkinje neuron synapse that occurs after brief stimulation of granule cell axons at 2–8 Hz. Previous work has shown that cerebellar LTP also may be seen when synaptic currents are evoked in granule cell-glial cell pairs in culture. This finding suggests a model in which cerebellar LTP is expressed presynaptically and therefore may be detected by either neuronal or glial postsynaptic cells. However, synaptic currents evoked in both granule cell-glial cell pairs and granule cell-Purkinje neuron pairs in culture are mediated primarily by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors, raising the possibility that cerebellar LTP might be expressed postsynaptically in both glial cells and Purkinje neurons in a similar manner. To address this question, glutamate transport currents were recorded in granule cell-glial cell pairs in culture by pharmacological isolation. These currents were increased by substitution of internal Cl with NO3 and were blocked by l-pyrrolidine-2,4-dicarboxylate, both characteristics of the major cloned Bergmann glial cell glutamate transporter, EAAT1. After acquisition of baseline responses, LTP of isolated transport current was evoked by stimulation at 4 Hz (100 pulses) and could be blocked by removal of external Ca during this stimulation. The expression of LTP was associated with a decrease in the rate of synaptic failures and a decrease in the degree of paired-pulse facilitation. These findings, when taken together with the previous observation that both Purkinje neuron and glial AMPA/kainate responses can be used to detect cerebellar LTP, strongly suggest that the expression of cerebellar LTP is, at least in part, presynaptic. This strategy should also be useful in illuminating the locus of expression of other model systems of information storage such as hippocampal LTP/long-term depression.
Different Combinations of GABAA and GABAC Receptors Confer Distinct Temporal Properties to Retinal Synaptic Responses
Authors: Lukasiewicz Peter D. , Shields Colleen R.
Published: December 2017

Lukasiewicz, Peter D. and Colleen R. Shields. Different combinations of GABAA and GABAC receptors confer distinct temporal properties to retinal synaptic responses. J. Neurophysiol. 79:3157–3167, 1998. This study addresses how γ-aminobutyric acid-A(GABAA) and GABAC receptors confer distinct temporal properties to neuronal synaptic responses. The retina is a model system for the study of postsynaptic contributions to synaptic responses because GABAergic amacrine cells synapse onto neurons, which have different combinations of GABAA and GABAC receptors. It is not known, however, how GABAA versus GABAC receptors influence the time course of retinal synaptic responses or what proportion of inhibitory input is mediated by each receptor type. We examined the time courses of synaptic responses mediated by GABA receptors in ganglion and bipolar cells by recording currents evoked by activating amacrine cells with a stimulating electrode in the salamander retinal slice. The pharmacologically isolated, GABAergic synaptic currents were long-lasting in bipolar cells and relatively brief in ganglion cells. The receptors that mediated these temporally distinct synaptic responses exhibited different pharmacological properties. In ganglion cells, GABAergic synaptic currents were abolished by the GABAA receptor antagonists bicuculline or SR95531. In bipolar cells, the GABAC receptor antagonist 3-aminopropyl[methyl]phosphonic acid (3-APMPA) largely blocked GABAergic synaptic responses; the remaining response was blocked by bicuculline or SR95531. The GABAA receptor component of the bipolar cell response was relatively brief compared with the GABAC receptor component. Puffing GABA onto ganglion cell dendrites or bipolar cell terminals yielded similar pharmacological and kinetic results, indicating that transmitter release differences did not determine the response time courses. Moreover, the GABAC receptors on bipolar cells may be different from those reported in rat or fish retina because imidazole-4-acetic acid (I4AA), which acts as an antagonist in these preparations, acts as an agonist in salamander. Our data show that the prolonged synaptic responses in bipolar cells were mediated predominantly by GABAC receptors, whereas transient synaptic responses in ganglion cells were mediated by GABAA receptors.
Commutative Saccadic Generator Is Sufficient to Control a 3-D Ocular Plant With Pulleys
Authors: Quaia Christian , Optican Lance M.
Published: December 2017

Quaia, Christian and Lance M. Optican. Commutative saccadic generator is sufficient to control a 3-D ocular plant with pulleys. J. Neurophysiol. 79: 3197–3215, 1998. One-dimensional models of oculomotor control rely on the fact that, when rotations around only one axis are considered, angular velocity is the derivative of orientation. However, when rotations around arbitrary axes [3-dimensional (3-D) rotations] are considered, this property does not hold, because 3-D rotations are noncommutative. The noncommutativity of rotations has prompted a long debate over whether or not the oculomotor system has to account for this property of rotations by employing noncommutative operators. Recently, Raphan presented a model of the ocular plant that incorporates the orbital pulleys discovered, and qualitatively modeled, by Miller and colleagues. Using one simulation, Raphan showed that the pulley model could produce realistic saccades even when the neural controller is commutative. However, no proof was offered that the good behavior of the Raphan-Miller pulley model holds for saccades different from those simulated. We demonstrate mathematically that the Raphan-Miller pulley model always produces movements that have an accurate dynamic behavior. This is possible because, if the pulleys are properly placed, the oculomotor plant (extraocular muscles, orbital pulleys, and eyeball) in a sense appears commutative to the neural controller. We demonstrate this finding by studying the effect that the pulleys have on the different components of the innervation signal provided by the brain to the extraocular muscles. Because the pulleys make the axes of action of the extraocular muscles dependent on eye orientation, the effect of the innervation signals varies correspondingly as a function of eye orientation. In particular, the Pulse of innervation, which in classical models of the saccadic system encoded eye velocity, here encodes a different signal, which is very close to the derivative of eye orientation. In contrast, the Step of innervation always encodes orientation, whether or not the plant contains pulleys. Thus the Step can be produced by simply integrating the Pulse. Particular care will be given to describing how the pulleys can have this differential effect on the Pulse and the Step. We will show that, if orbital pulleys are properly located, the neural control of saccades can be greatly simplified. Furthermore, the neural implementation of Listing's Law is simplified: eye orientation will lie in Listing's Plane as long as the Pulse is generated in that plane. These results also have implications for the surgical treatment of strabismus.
fMRI Study of Face Perception and Memory Using Random Stimulus Sequences
Authors: Clark Vincent P. , Maisog Jose M. , Haxby James V.
Published: December 2017

Clark, Vincent P., Jose M. Maisog, and James V. Haxby. fMRI study of face perception and memory using random stimulus sequences. J. Neurophysiol. 79: 3257–3265, 1998. A new functional magnetic resonance imaging (fMRI) method was used to investigate the functional neuroanatomy of face perception and memory. Whole-brain fMRI data were acquired while four types of stimuli were presented sequentially in an unpredictable pseudorandom order at a rate of 0.5 Hz. Stimulus types were a single repeated memorized target face, unrepeated novel faces, nonsense scrambled faces, and a blank screen. Random stimulus sequences were designed to generate a functional response to each stimulus type that was uncorrelated with responses to other stimuli. This allowed fMRI responses to each stimulus type to be examined separately using multiple regression. Signal increases were found for all stimuli in ventral posterior cortex. Responses to intact faces extended to more anterior locations of occipitotemporal cortex than did responses to scrambled faces, consistent with previous studies of face perception. Responses evoked by novel faces were in regions of ventral occipitotemporal cortex medial to regions in which significant responses were evoked by the target face. The repeated target face stimulus also evoked activity in widely distributed regions of frontal and parietal cortex. These results demonstrate that cortical hemodynamic responses to interleaved novel and repeated stimuli can be distinguished and measured using fMRI with appropriate stimulus sequences and data analysis methods. This method can now be used to examine the neural systems involved in cognitive tasks that were previously impossible to study using positron emission tomography or fMRI.
Signal Timing Across the Macaque Visual System
Authors: Schmolesky Matthew T. , Wang Youngchang , Hanes Doug P. , Thompson Kirk G. , Leutgeb Stefan , Schall Jeffrey D. , Leventhal Audie G.
Published: December 2017

Schmolesky, Matthew T., Youngchang Wang, Doug P. Hanes, Kirk G. Thompson, Stefan Leutgeb, Jeffrey D. Schall, and Audie G. Leventhal. Signal timing across the macaque visual system. J. Neurophysiol. 79: 3272–3278, 1998. The onset latencies of single-unit responses evoked by flashing visual stimuli were measured in the parvocellular (P) and magnocellular (M) layers of the dorsal lateral geniculate nucleus (LGNd) and in cortical visual areas V1, V2, V3, V4, middle temporal area (MT), medial superior temporal area (MST), and in the frontal eye field (FEF) in individual anesthetized monkeys. Identical procedures were carried out to assess latencies in each area, often in the same monkey, thereby permitting direct comparisons of timing across areas. This study presents the visual flash-evoked latencies for cells in areas where such data are common (V1 and V2), and are therefore a good standard, and also in areas where such data are sparse (LGNd M and P layers, MT, V4) or entirely lacking (V3, MST, and FEF in anesthetized preparation). Visual-evoked onset latencies were, on average, 17 ms shorter in the LGNd M layers than in the LGNd P layers. Visual responses occurred in V1 before any other cortical area. The next wave of activation occurred concurrently in areas V3, MT, MST, and FEF. Visual response latencies in areas V2 and V4 were progressively later and more broadly distributed. These differences in the time course of activation across the dorsal and ventral streams provide important temporal constraints on theories of visual processing.
Synaptic Transmission and Hippocampal Long-Term Potentiation in Olfactory Cyclic Nucleotide-Gated Channel Type 1 Null Mouse
Authors: Parent Angèle , Schrader Karen , Munger Steven D. , Reed Randall R. , Linden David J. , Ronnett Gabriele V.
Published: December 2017

Parent, Angèle, Karen Schrader, Steven D. Munger, Randall R. Reed, David J. Linden, and Gabriele V. Ronnett. Synaptic transmission and hippocampal long-term potentiation in olfactory cyclic nucleotide-gated channel type 1 null mouse. J. Neurophysiol. 79: 3295–3301, 1998. Field potential recording was used to investigate properties of synaptic transmission and long-term potentiation (LTP) at Schaffer collateral-CA1 synapses in both hippocampal slices of mutant mice in which the α-subunit of the olfactory cyclic nucleotide-gated channel (α3/OCNC)1 was rendered null and also in slices prepared from their wild-type (Wt) littermates. Several measures of basal synaptic transmission were unaltered in the OCNC1 knockout (KO), including maximum field excitatory postsynaptic potential (fEPSP) slope, maximum fEPSP and fiber volley amplitude, and the function relating fiber volley amplitude to fEPSP slope and paired-pulse facilitation. When a high-frequency stimulation protocol was used to induce LTP, similar responses were seen in both groups [KO: 1 min, 299 ± 50% (mean ± SE), 60 min, 123 ± 10%; Wt: 1 min, 287 ± 63%; 60 min, 132 ± 19%). However, on theta-burst stimulation, the initial amplitude of LTP was smaller (1 min after induction, 147 ± 16% of baseline) and the response decayed faster in the OCNC1 KO (60 min, 127 ± 18%) than in Wt (1 min, 200 ± 14%; 60 min, 169 ± 19%). Analysis of waveforms evoked by LTP-inducing tetanic stimuli revealed a similar difference between groups. The development of potentiation throughout the tetanic stimulus was similar in OCNC1 KO and Wt mice when high-frequency stimulation was used, but OCNC1 KO mice showed a significant decrease when compared with Wt mice receiving theta-burst stimulation. These results suggest that activation of cyclic nucleotide-gated channels may contribute to the induction of LTP by weaker, more physiological stimuli, possibly via Ca2+ influx.
Substance P-Induced Inward Current in Identified Auditory Efferent Neurons in Rat Brain Stem Slices
Authors: Wang Xueyong , Robertson Donald
Published: December 2017

Wang, Xueyong and Donald Robertson. Substance P-induced inward current in identified auditory efferent neurons in rat brain stem slices. J. Neurophysiol. 80: 218–229, 1998. The effects of substance P (SP) on whole cell currents were studied in neurons of the medial olivocochlear efferent system (MOCS) in the ventral nucleus of the trapezoid body (VNTB) of brain stem slices from neonatal rats. Each neuron was identified by retrograde labeling with Fast Blue injected into the cochlea. Bath application of SP (0.1–10 μM) reversibly induced an apparent inward current in 49 of 63 labeled neurons when voltage clamped at near resting voltages. This apparent inward current was consistent with the SP-induced membrane depolarization observed in current-clamp mode. The SP-induced change in current was dose dependent with a half-maximal response dose of 200 nM. It was mimicked by [Cys3,6, Tyr8, Pro9]-SP, a neurokinin (NK1) receptor selective agonist, whereas [Succinyl-Asp6, MePhe8]-SP 6–11 (Senktide), a NK3 receptor agonist, had no detectable effect. The SP effect was not blocked by 10-6 M tetrodotoxin (TTX) and persisted when the perfusate contained 30 mM tetraethylammonium (TEA) or 100 μM Cd2+ or was in a 0-Ca solution. In a TTX-containing solution, SP caused a voltage-dependent decrease of membrane conductance, and the SP-evoked current reversed at a potential at around −105 mV. The predicted K+ equilibrium potential was −93.8 mV under the experimental conditions. The SP-induced inward current was attenuated by 66% when the perfusate contained 3 mM Cs+. We conclude that the apparent inward current is partly caused by SP decreasing an outward current normally maintained by the inward rectifier K+ channels in these cells. In the presence of Cs solution in the recording pipette and with a perfusate containing 3 mM Cs+, 0.1 mM Cd2+ and 10-6 M TTX, a residual SP-induced inward current was observed at test voltages ranging from −120 to 40 mV. This subcomponent reversed its polarity at ∼20 mV. This inward current was reduced substantially (but not abolished) when all NaCl in the external solution was replaced by TEA-Cl. The results indicate that SP also opens an unknown cation channel, which the available data suggests may be relatively nonselective. The results suggest that MOCS neurons are subject to modulation by SP, which depolarizes the cell membrane by decreasing the activity of inward rectifier K+ channels as well as concurrently activating a separate cation conductance. It also was found that in MOCS neurons responsive to both SP and norepinephrine, the norepinephrine effect was abolished by TTX, suggesting that an interneuronal population excited by norepinephrine converges selectively onto SP-sensitive MOCS neurons in the VNTB.
Cell-Permeable Scavengers of Superoxide Prevent Long-Term Potentiation in Hippocampal Area CA1
Authors: Klann Eric
Published: December 2017

Klann, Eric. Cell-permeable scavengers of superoxide prevent long-term potentiation in hippocampal area CA1. J. Neurophysiol. 80: 452–457, 1998. Long-term potentiation (LTP) in hippocampal area CA1 is generally dependent on N-methyl-d-aspartate (NMDA) receptor activation. Reactive oxygen species (ROS), including superoxide, are produced in response to NMDA receptor activation in a number of brain regions, including the hipppocampus. In this study, two cell-permeable manganese porphyrin compounds that mimic superoxide dismutase (SOD) were used to determine whether production of superoxide is required for the induction of LTP in area CA1 of rat hippocampal slices. Incubation of hippocampal slices with either Mn(III) tetrakis (4-benzoic acid) porphyrin (MnTBAP) or Mn(III) tetrakis (1-methyl-4-pyridyl) porphyrin (MnTMPyP) prevented the induction of LTP. Incubation of slices with either light-inactivated MnTBAP or light-inactivated MnTMPyP had no effect on induction of LTP. Neither MnTBAP nor MnTMPyP was able to reverse preestablished LTP. These observations suggest that production of superoxide occurs in response to LTP-inducing stimulation and that superoxide is necessary for the induction of LTP.
Modulation of the Inspiratory-Related Activity of Hypoglossal Premotor Neurons During Ingestion and Rejection in the Decerebrate Cat
Authors: Ono Takashi , Ishiwata Yasuo , Inaba Noritaka , Kuroda Takayuki , Nakamura Yoshio
Published: December 2017

Ono, Takashi, Yasuo Ishiwata, Noritaka Inaba, Takayuki Kuroda, and Yoshio Nakamura. Modulation of the inspiratory-related activity of hypoglossal premotor neurons during ingestion and rejection in the decerebrate cat. J. Neurophysiol. 80: 48–58, 1998. Single-unit activities of the bulbar reticular inspiratory neurons directly projecting to hypoglossal motoneurons were studied during fictive ingestion (e.g., swallowing) and rejection elicited by repetitive stimulation of the superior laryngeal nerve and by application of water to the pharynx in immobilized decerebrated cats. The single-unit activity was recorded during 113 episodes of fictive ingestion from 25 inspiratory neurons directly projecting to hypoglossal motoneurons (single projection neurons) and 7 inspiratory neurons directly projecting to both hypoglossal and phrenic motoneurons (dual projection neurons) in the regions ventrolateral to the nucleus tractus solitarii and dorsomedial to the nucleus ambiguus. All of single projection neurons ceased inspiratory-related rhythmical discharges coincidentally with the onset of repetitive stimulation of the superior laryngeal nerve. The majority of them (19/25, 76%, type A) showed a spike burst during ingestion, whereas the minority (6/25, 24%, type B) kept silent until the end of repetitive stimulation of the superior laryngeal nerve. During fictive ingestion elicited by application of water to the pharynx, the type-A neurons showed a spike burst activity, whereas the type-B neurons kept silent. All dual projection neurons (7/7, 100%, type C) ceased inspiratory-related rhythmical discharges at the onset of repetitive stimulation of the superior laryngeal nerve and showed no activity during fictive ingestion. Likewise, the type-C neurons kept silent during fictive ingestion elicited by application of water to the pharynx. A spike burst was induced during 33 episodes of fictive rejection in all of 5 tested type-A, 3 tested type-B, and 6 tested type-C neurons. It is concluded that the premotor neurons involved in the respiratory-related rhythmical activity of hypoglossal motoneurons is responsible for switching from respiration to ingestion and rejection.
Full Weight-Bearing Hindlimb Standing Following Stand Training in the Adult Spinal Cat
Authors: De Leon R. D. , Hodgson J. A. , Roy R. R. , Edgerton V. R.
Published: December 2017

De Leon, R. D., J. A. Hodgson, R. R. Roy, and V. R. Edgerton. Full weight-bearing hindlimb standing following stand training in the adult spinal cat. J. Neurophysiol. 80: 83–91, 1998. Behavioral and physiological characteristics of standing were studied in nontrained spinal cats and in spinal cats that received daily stand training of the hindlimbs for 12 wk. Training consisted of assisting the cats to stand with full weight support either on both hindlimbs or on one hindlimb (30 min/day, 5 days/wk). Extensor muscle electromyographic (EMG) amplitude and extension at the knee and ankle joints during full weight bearing recovered to prespinal levels in both stand-trained and nontrained spinal cats. However, full weight bearing of the hindquarters was sustained for up to ∼20 min in the spinal cats that received bilateral stand training compared with ∼4 min in cats that were not trained to stand. Unilateral stand training selectively improved weight bearing on the trained limb based on ground reaction forces and extensor muscle EMG activity levels measured during bilateral standing. These results suggest that the capacity of the adult lumbar spinal cord to generate full weight-bearing standing can be improved by as much as fivefold by the repetitive activation of selected neural pathways in the spinal cord after supraspinal connectivity has been eliminated. Given that stepping is improved in response to step training, it appears that the recovery of standing provides another example of training-specific motor learning in the spinal cord, i.e., the spinal cord learns to perform hindlimb standing by practicing that specific task.
Synaptic Interactions Between Crista Hair Cells in the Statocyst of the SquidAlloteuthis subulata
Authors: Chrachri Abdesslam , Williamson Roddy
Published: December 2017

Chrachri, Abdesslam and Roddy Williamson. Synaptic interactions between crista hair cells in the statocyst of the squid Alloteuthis subulata. J. Neurophysiol. 80: 656–666, 1998. Intracellular injections of the fluorescent dye Lucifer yellow into the various cell types within the anterior transverse crista segment of the statocyst of squid revealed that the primary sensory hair cells and both large and small first-order afferent neurons have relatively simple morphologies, each cell having a single, unbranched axon that passes directly into the small crista nerve that innervates the anterior transverse crista. However, the small first-order neurons have short dendritic processes occurring in the region of the sensory hair cells. The secondary sensory hair cells have no centripetal axons, but some have long processes extending from their bases along the segment. Simultaneous intracellular recordings from pairs of the different cell types in the anterior transverse crista segment demonstrated that electrical coupling is widespread; secondary sensory hair cells are coupled electrically along a hair cell row, as are groups of primary sensory hair cells. Secondary sensory hair cell also are coupled to neighboring small first-order afferent neurons. However, this coupling is rectifying in that it only occurs from secondary sensory hair cells to first-order afferent neurons. Direct electrical stimulation of the small crista nerve to excite the efferent axons revealed efferent connections to both the primary sensory hair cells and the small first-order afferent neurons. These efferent responses were of three types: excitatory or inhibitory postsynaptic potentials and excitatory postsynaptic potentials followed by inhibitory postsynaptic potentials. The functional significance of the cell interactions within the crista epithelium of the statocyst of squid is discussed and comparisons drawn with the balance organs of other animals.