bluuebunny/crossref_metadata_2025 huggingface dataset:
Recruitment of GABAergic Inhibition and Synchronization of Inhibitory Interneurons in Rat Neocortex
Authors: Benardo Larry S.
Published: December 2017

Benardo, Larry S. Recruitment of GABAergic inhibition and synchronization of inhibitory interneurons in rat neocortex. J. Neurophysiol. 77: 3134–3144, 1997. Intracellular recordings were obtained from pyramidal and interneuronal cells in rat neocortical slices to examine the recruitment of GABAergic inhibition and inhibitory interneurons. In the presence of the convulsant agent4-aminopyridine (4-AP), after excitatory amino acid (EAA) ionotropic transmission was blocked, large-amplitude triphasic inhibitory postsynaptic potentials (IPSPs) occurred rhythmically (every 10–40 s) and synchronously in pyramidal neurons. After exposure to the γ-aminobutyric acid-A (GABAA) receptor antagonist picrotoxin, large-amplitude monophasic slow IPSPs persisted in these cells. In the presence of 4-AP and EAA blockers, interneurons showed periodic spike firing. Although some spikes rode on an underlying synaptic depolarization, much of the rhythmic firing consisted of spikes having highly variable amplitudes, arising abruptly from baseline, even during hyperpolarization. The spike firing and depolarizing synaptic potentials were completely suppressed by picrotoxin exposure, although monophasic slow IPSPs persisted in interneurons. This suggests that this subset of interneurons may participate in generating fast GABAA IPSPs, but not slow GABAB IPSPs. Cell morphology was confirmed by intracellular injection of neurobiotin or the fluorescent dye Lucifer yellow CH. Dye injection into interneurons often (>70%) resulted in the labeling of two to six cells (dye coupling). These findings suggest that GABAAergic neurons may be synchronized via recurrent collaterals through the depolarizing action of synaptically activatedGABAA receptors and a mechanism involving electrotonic coupling. Although inhibitory neurons mediating GABAB IPSPs may be entrained by the excitatory GABAA mechanism, they appear to be a separate subset of GABAergic neurons capable of functioning independently with autonomous pacing.
Spatial Memory and Path Integration Studied by Self-Driven Passive Linear Displacement. I. Basic Properties
Authors: Israël I. , Grasso R. , Georges-François P. , Tsuzuku T. , Berthoz A.
Published: December 2017

Israël, I., R. Grasso, P. Georges-François, T. Tsuzuku, and A. Berthoz. Spatial memory and path integration studied by self-driven passive linear displacement. I. Basic properties. J. Neurophysiol. 77: 3180–3192, 1997. According to path integration, the brain is able to compute the distance of a traveled path. In this research we applied our previously reported method for studying memory of linear distance, a crucial mechanism in path integration; our method is based on the overt reconstruction of a passive transport. Passive transport is a special case of navigation in which no active control is performed. Blindfolded subjects were first asked to travel 2 m forward, in darkness, by driving with a joystick the robot on which they were seated. The results show that all subjects but two undershot this distance, i.e., overestimated their own displacement. Then, subjects were submitted to a passive linear forward displacement along 2, 4, 6, 8, or 10 m, and had to reproduce the same distance, still blindfolded. The results show that the distance of the stimulus was accurately reproduced, as well as stimulus duration, peak velocity, and velocity profile. In this first condition, the imposed velocity profile was triangular and therefore stimulus distance and duration were correlated. In a second condition, it was shown that distance was correctly reproduced also when the information about stimulus duration was kept constant. Here, different velocity profiles were used as stimuli, and most subjects also reproduced the velocity profile. Statistical analyses indicated that distance was not reproduced as a consequence of duration, peak velocity, or velocity profile reproduction, but was uniquely correlated to stimulus distance. The previous hypothesis of a double integration of the otolith signal to provide a distance estimate can explain our results. There was a large discrepancy between the accuracy with which the subjects matched the velocity profiles and that of distance reproduction. It follows that, whereas the dynamics of passive motion are stored and available to further use, distance is independently estimated. It is concluded that vestibular and somatosensory signals excited by passive transport can be used to build a dynamic as well as a static representation of the traveled path. We found a close quantitative similarity between the present findings on distance reproduction and those obtained from active locomotion experiments in which the same paradigm was used. This resemblance suggests that the two types of navigation tasks draw on common physiological processes and extends the relevance of our results to naturally occurring path integration.
Implications of Positive Feedback in the Control of Movement
Authors: Prochazka Arthur , Gillard Deborah , Bennett David J.
Published: December 2017

Prochazka, Arthur, Deborah Gillard, and David J. Bennett. Implications of positive feedback in the control of movement. J. Neurophysiol. 77: 3237–3251, 1997. In this paper we review some theoretical aspects of positive feedback in the control of movement. The focus is mainly on new theories regarding the reflexive role of sensory signals from mammalian tendon organ afferents. In static postures these afferents generally mediate negative force feedback. But in locomotion there is evidence of a switch to positive force feedback action. Positive feedback is often associated with instability and oscillation, neither of which occur in normal locomotion. We address this paradox with the use of analytic models of the neuromuscular control system. It is shown that positive force feedback contributes to load compensation and is surprisingly stable because the length-tension properties of mammalian muscle provide automatic gain control. This mechanism can stabilize control even when positive feedback is very strong. The models also show how positive force feedback is stabilized by concomitant negative displacement feedback and, unexpectedly, by delays in the positive feedback pathway. Other examples of positive feedback in animal motor control systems are discussed, including the β-fusimotor system, which mediates positive feedback of displacement. In general it is seen that positive feedback reduces the sensitivity of the controlled extremities to perturbations of posture and load. We conclude that positive force feedback can provide stable and effective load compensation that complements the action of negative displacement and velocity feedback.
Quantitative Analysis of Orofacial Thermoreceptive Neurons in the Superficial Medullary Dorsal Horn of the Rat
Authors: Hutchison W. D. , Tsoukatos J. , Dostrovsky J. O.
Published: December 2017

Hutchison, W. D., J. Tsoukatos, and J. O. Dostrovsky. Quantitative analysis of orofacial thermoreceptive neurons in the superficial medullary dorsal horn of the rat. J. Neurophysiol. 77: 3252–3266, 1997. Surprisingly little is known concerning the central processing of innocuous thermal somatosensory information. The aim of the present study was to obtain quantitative data on the characteristics of neurons in the rat superficial medullary dorsal horn (sMDH) that responded to innocuous thermal stimulation of the rat's face and tongue. Single-unit extracellular recordings were obtained in chloralose-urethane anesthetized rats. A total of 153 thermoreceptive neurons was studied. Of these, 146 were excited by cooling and inhibited by warming and were classified as COLD cells. The remaining seven cells were excited by innocuous warming of the skin or tongue. Of 123 COLD cells tested, 33% were excited by touch and 22% by pinch stimuli delivered to the thermoreceptive field. Of the 50 COLD cells tested, 46% were excited also by noxious heating (≥50°C for 5 s). Most (82/121) of the receptive fields were located on the upper lip, 25 on the tongue, and most of the remaining on the lower lip. Receptive fields were generally small (1–5 mm2). In some experiments, electrical stimulation in the thalamus was performed, and nine COLD cells could be activated antidromically. The responses of 38 COLD cells to incremental 5°C cooling steps were examined quantitatively. Thermal stimuli were applied to facial or lingual receptive fields of sMDH neurons with a computer-controlled Peltier thermode starting from 33°C, decreasing to 8 or 3°C, and returning to 33°C. Most COLD cells (26/38) had both static and dynamic responses; 7 had mainly dynamic and 5 mainly static responses to step decreases in temperature. Rat sMDH COLD cells could be classified into three groups depending on their stimulus-response functions. The first group ( Type 1, n = 19) had a bell-shaped static stimulus response function. The second group ( Type 2) had a high maintained or increasing static firing rate as the temperature decreased <18°C ( n = 10). Type 3 COLD cells had mainly dynamic properties ( n = 7). Many of the cells in all groups were excited by noxious mechanical stimulation. Type 2 cells differed from the other two groups in that most did not respond to noxious thermal stimuli (hot) and many responded to innocuous tactile stimuli. Neurons from each of the three groups of COLD cells could be activated antidromically from contralateral thalamus. These data suggest that there is little central processing of thermal information at the first central synapse for Type 1 neurons, however, the responses of the other two types may be due to central processing and convergence. The demonstration of rat sMDH COLD cells with distinctive stimulus-response functions to thermal shifts suggests separate functional roles of these neurons in the ascending thermal sensory pathway.
Noradrenergic Suppression of Synaptic Transmission May Influence Cortical Signal-to-Noise Ratio
Authors: Hasselmo Michael E. , Linster Christiane , Patil Madhvi , Ma Daveena , Cekic Milos
Published: December 2017

Hasselmo, Michael E., Christiane Linster, Madhvi Patil, Daveena Ma, and Milos Cekic. Noradrenergic suppression of synaptic transmission may influence cortical signal-to-noise ratio. J. Neurophysiol. 77: 3326–3339, 1997. Norepinephrine has been proposed to influence signal-to-noise ratio within cortical structures, but the exact cellular mechanisms underlying this influence have not been described in detail. Here we present data on a cellular effect of norepinephrine that could contribute to the influence on signal-to-noise ratio. In brain slice preparations of the rat piriform (olfactory) cortex, perfusion of norepinephrine causes a dose-dependent suppression of excitatory synaptic potentials in the layer containing synapses among pyramidal cells in the cortex (layer Ib), while having a weaker effect on synaptic potentials in the afferent fiber layer (layer Ia). Effects of norepinephrine were similar in dose-response characteristics and laminar selectivity to the effects of the cholinergic agonist carbachol, and combined perfusion of both agonists caused effects similar to an equivalent concentration of a single agonist. In a computational model of the piriform cortex, we have analyzed the effect of noradrenergic suppression of synaptic transmission on signal-to-noise ratio. The selective suppression of excitatory intrinsic connectivity decreases the background activity of modeled neurons relative to the activity of neurons receiving direct afferent input. This can be interpreted as an increase in signal-to-noise ratio, but the term noise does not accurately characterize activity dependent on the intrinsic spread of excitation, which would more accurately be described as interpretation or retrieval. Increases in levels of norepinephrine mediated by locus coeruleus activity appear to enhance the influence of extrinsic input on cortical representations, allowing a pulse of norepinephrine in an arousing context to mediate formation of memories with a strong influence of environmental variables.
Primary Afferent Depolarizations of Sensory Origin Within Contact-Sensitive Mechanoreceptive Afferents of a Crayfish Leg
Authors: Marchand A. R. , Barnes W.J.P. , Cattaert D.
Published: December 2017

Marchand, A. R., W.J.P. Barnes, and D. Cattaert. Primary afferent depolarizations of sensory origin within contact-sensitive mechanoreceptive afferents of a crayfish leg: properties, quantal analysis, and role in presynaptic integration. J. Neurophysiol. 77: 3340–3354, 1997. Recordings from the central branches of single identified dactyl sensory afferent (DSA) neurons in a crayfish in vitro preparation were performed to study modifications of the sensory message occurring before the first central synapse. These afferents comprised hairs and force-sensitive mechanoreceptors with phasic and phasotonic response characteristics in the terminal segment (dactyl) of the crayfish leg. More than one afferent spike size was often observed in intracellular recordings from these afferents, thus indicating the presence of electrical coupling between the central processes of DSA fibers. Additionally, in identified DSA fibers with large spike sizes, primary afferent depolarizations (PADs) of up to 15 mV were observed, which sometimes triggered antidromic spikes in the afferent. Nevertheless, PADs were clearly inhibitory, because they shunted the afferent spikes. They exhibited the following properties. First, each PAD was preceded by an afferent spike from a neighboring hair, indicating that the PADs had a sensory rather than central origin. Second, PADs could follow high frequencies of afferent discharges without failure, a property suggestive of monosynaptic connections, but because PAD latencies varied by ±0.5 ms it is more likely that they were mediated by a disynaptic pathway. Third, although PADs were evoked in an extremely reliable manner, their amplitude varied in a quantal manner. Most unitary PADs were the result of the release of <12 quanta, the mean quantal content lying between 4 and 5; quantal size was large, ∼1 mV. Fourth, PADs showed facilitation in some fibers, whereas in others they became much smaller when occurring at brief intervals. We suggest that PADs may be an efficient and parsimonious way to limit sensory inflow in space and time, allowing the crayfish to identify precisely both weak and strong mechanical stimuli.
Ocular Dominance Peaks at Pinwheel Center Singularities of the Orientation Map in Cat Visual Cortex
Authors: Crair Michael C. , Ruthazer Edward S. , Gillespie Deda C. , Stryker Michael P.
Published: December 2017

Crair, Michael C., Edward S. Ruthazer, Deda C. Gillespie, and Michael P. Stryker. Ocular dominance peaks at pinwheel center singularities of the orientation map in cat visual cortex. J. Neurophysiol. 77: 3381–3385, 1997. In the primary visual cortex of monkey and cat, ocular dominance and orientation are represented continuously and simultaneously, so that most neighboring neurons respond optimally to visual stimulation of the same eye and orientation. Maps of stimulus orientation are punctuated by singularities referred to as “pinwheel centers,” around which all orientations are represented. Given that the orientation map is mostly continuous, orientation singularities are a mathematical necessity unless the map consists of perfectly parallel rows, and there is no evidence that the singularities play a role in normal function or development. We report here that in cats there is a strong tendency for peaks of ocular dominance to lie on the pinwheel center singularities of the orientation map. This relationship predicts but is not predicted by the tendencies, previously reported, for pinwheels to lie near the center lines of ocular dominance bands and for iso-orientation bands to cross ocular dominance boundaries at right angles. The coincidence of ocular dominance peaks with orientation singularities is likely to reflect a strong underlying functional link between the two visual cortical maps.
Cortical Control of Human Motoneuron Firing During Isometric Contraction
Authors: Salenius Stephan , Portin Karin , Kajola Matti , Salmelin Riitta , Hari Riitta
Published: December 2017

Salenius, Stephan, Karin Portin, Matti Kajola, Riitta Salmelin, and Riitta Hari. Cortical control of human motoneuron firing during isometric contraction. J. Neurophysiol. 77: 3401–3405, 1997. We recorded whole scalp magnetoencephalographic (MEG) signals simultaneously with the surface electromyogram from upper and lower limb muscles of six healthy right-handed adults during voluntary isometric contraction. The 15- to 33-Hz MEG signals, originating from the anterior bank of the central sulcus, i.e., the primary motor cortex, were coherent with motor unit firing in all subjects and for all muscles. The coherent cortical rhythms originated in the hand motor area for upper limb muscles (1st dorsal interosseus, extensor indicis proprius, and biceps brachii) and close to the foot area for lower limb muscles (flexor hallucis brevis). The sites of origin corresponding to different upper limb muscles did not differ significantly. The cortical signals preceded motor unit firing by 12–53 ms. The lags were shortest for the biceps brachii and increased systematically with increasing corticomuscular distance. We suggest that the motor cortex drives the spinal motoneuronal pool during sustained contractions, with the observed cortical rhythmic activity influencing the timing of efferent commands. The cortical rhythms could be related to motor binding, but the rhythmic output may also serve to optimize motor cortex output during isometric contractions.
Wrist Action Affects Precision Grip Force
Authors: Werremeyer Mary M. , Cole Kelly J.
Published: December 2017

Werremeyer, Mary M. and Kelly J. Cole. Wrist action affects precision grip force. J. Neurophysiol. 78: 271–280, 1997. When moving objects with a precision grip, fingertip forces normal to the object surface (grip force) change in parallel with forces tangential to the object (load force). We investigated whether voluntary wrist actions can affect grip force independent of load force, because the extrinsic finger muscles cross the wrist. Grip force increased with wrist angular speed during wrist motion in the horizontal plane, and was much larger than the increased tangential load at the fingertips or the reaction forces from linear acceleration of the test object. During wrist flexion the index finger muscles in the hand and forearm increased myoelectric activity; during wrist extension this myoelectric activity increased little, or decreased for some subjects. The grip force maxima coincided with wrist acceleration maxima, and grip force remained elevated when subjects held the wrist in extreme flexion or extension. Likewise, during isometric wrist actions the grip force increased even though the fingertip loads remained constant. A grip force “pulse” developed that increased with wrist force rate, followed by a static grip force while the wrist force was sustained. Subjects could not suppress the grip force pulse when provided visual feedback of their grip force. We conclude that the extrinsic hand muscles can be recruited to assist the intended wrist action, yielding higher grip-load ratios than those employed with the wrist at rest. This added drive to hand muscles overcame any loss in muscle force while the extrinsic finger flexors shortened during wrist flexion motion. During wrist extension motion grip force increases apparently occurred from eccentric contraction of the extrinsic finger flexors. The coactivation of hand closing muscles with other wrist muscles also may result in part from a general motor facilitation, because grip force increased during isometric knee extension. However, these increases were related weakly to the knee force. The observed muscle coactivation, from all sources, may contribute to grasp stability. For example, when transporting grasped objects, upper limb accelerations simultaneously produce inertial torques at the wrist that must be resisted, and inertial loads at the fingertips from the object that must be offset by increased grip force. The muscle coactivation described here would cause similarly timed pulses in the wrist force and grip force. However, grip-load coupling from this mechanism would not contribute much to grasp stability when small wrist forces are required, such as for slow movements or when the object's total resistive load is small.
Role of Calcium-Calmodulin–Dependent Protein Kinase II in Modulation of Sensorimotor Synapses inAplysia
Authors: Nakanishi Keiko , Zhang Fan , Baxter Douglas A. , Eskin Arnold , Byrne John H.
Published: December 2017

Nakanishi, Keiko, Fan Zhang, Douglas A. Baxter, Arnold Eskin, and John H. Byrne. Role of calcium-calmodulin–dependent protein kinase II in modulation of sensorimotor synapses in Aplysia. J. Neurophysiol. 78: 409–416, 1997. The Ca2+-calmodulin–dependent protein kinase II (CaMKII) inhibitor, {1-[N,O - bis(5 - isoquinolinesulfonyl) - N - methyl - L - tyrosyl] - 4 - phenylpiper azine} (KN-62), was used to investigate the role of CaMKII in synaptic transmission and serotonin (5-HT)-induced facilitation in Aplysia. Application of KN-62 (10 μM) by itself increased the amplitude of excitatory postsynaptic potentials (EPSPs) at sensorimotor synapses in pleural-pedal ganglia. Moreover, in the presence of KN-62, 5-HT–induced short-term facilitation was attenuated. Application of KN-62 by itself slightly increased the duration of action potentials in isolated sensory neuron somata but did not block spike broadening produced by 5-HT. KN-62 had no effect on excitability of isolated sensory neuron somata nor did it block 5-HT–induced enhancement of excitability. These results indicate that the attenuation of short-term facilitation by KN- 62 is not due to modulation of the membrane currents contributing to 5-HT–induced spike broadening or enhancement of excitability. Rather, these data are consistent with the hypothesis that CaMKII contributes to the regulation of sensorimotor connections and that it has a role in spike-duration–independent processes contributing to short-term facilitation.
Facilitation at the Lobster Neuromuscular Junction: A Stimulus-Dependent Mobilization Model
Authors: Worden Mary Kate , Bykhovskaia Maria , Hackett John T.
Published: December 2017

Worden, Mary Kate, Maria Bykhovskaia, and John T. Hackett. Facilitation at the lobster neuromuscular junction: a stimulus-dependent mobilization model. J. Neurophysiol. 78: 417–428, 1997. Frequency facilitation is a process whereby neurosecretion increases as a function of stimulation frequency during repetitive synaptic activity. To examine the physiological basis underlying facilitation, we have estimated the frequency dependence of the synaptic parameters n (number of units capable of responding to a nerve impulse) and P (average probability of responding) at the lobster neuromuscular junction. Both n and P increase as a function of frequency, suggesting that the efficiency of quantal docking and quantal fusion is regulated by repetitive synaptic activity. In experiments in which facilitation is strong and quantal content does not saturate over the frequency range tested, the value of P saturates at low frequencies of stimulation, and increases in quantal content at higher frequencies of stimulation are due to an increase in n. Therefore the value of P does not limit facilitation. We propose that transmitter release is limited by the rates of quantal mobilization and demobilization, and that each excitatory stimulus causes additional mobilization of quanta to dock at the presynaptic release sites. In such a model the binomial parameter n will correspond to the number of quanta docked at the release sites and available for release. We have developed and solved kinetic equations that describe how the number of docked quanta changes as a function of time and of stimulation frequency. The stimulus-dependent mobilization model of facilitation predicts that the reciprocal value of the quantal content depends linearly on the reciprocal product of the stimulation frequency and the probability of release. Fits of the experimental data confirm the accuracy of this prediction, showing that the model proposed here quantitatively describes frequency facilitation. The model predicts that high rates of quantal demobilization will produce strong frequency facilitation.
Tensile and Compressive Responses of Nociceptors in Rat Hairy Skin
Authors: Khalsa Partap S. , Lamotte Robert H. , Grigg Peter
Published: December 2017

Khalsa, Partap S., Robert H. LaMotte, and Peter Grigg. Tensive and compressive responses of nociceptors in rat hairy skin. J. Neurophysiol. 78: 492–505, 1997. Mechanically sensitive nociceptor afferents were studied in a preparation of isolated skin from rat leg. Each neuron was studied while the skin was subjected to tensile and compressive loading. The experiment was designed to create highly uniform states of stress in both tension and compression. Tensile loads were applied by pulling on the edges of the sample. Applied loads were used to determine the tensile stresses. Surface displacements were used to determine tensile strains. Compressive loads were applied by indenting the surface of the skin with flat indenter tips applied under force control. The skin was supported by a flat, hard substrate. Compressive stresses were determined from the applied loads and tip geometry. Compressive strains were determined from skin thickness and tip excursions. All nociceptors were activated by both tensile and compressive loading. There was no interaction between the responses to compressive and tensile stimuli (i.e., the responses were simply additive). Responses of nociceptors were better related to tensile and compressive stresses than to strains. Nociceptors responded better to tensile loading than to compressive loading. Response thresholds were lower and sensitivities were higher for tensile stress than for compressive stress. The response to compression was better related to compressive stress than to other stimulus parameters (i.e., load/circumference or simply load). Indentations of intact skin over a soft substrate such as muscle would be expected to cause widespread activation of nociceptors because of tensile stresses.
Contextual Conditioned Fear Blocks the Induction But Not the Maintenance of Lateral Septal LTP in Behaving Mice
Authors: Garcia René , Vouimba Rose Marie , Jaffard Robert
Published: December 2017

Garcia, René, Rose Marie Vouimba, and Robert Jaffard. Contextual conditioned fear blocks the induction but not the maintenance of lateral septal LTP in behaving mice. J. Neurophysiol. 78: 76–81, 1997. High-frequency stimulation (HFS) of the fimbria induces long-term potentiation (LTP) in the lateral septum. This study was aimed at investigating the effect of contextual fear conditioning on septal LTP with the use of behaving C57 BL/6 mice as subjects. For the acquisition of contextual fear conditioning, animals were placed in a conditioning chamber, where they were subjected to footshocks (FSs, 0.6 mA); the following day (retention), animals were reexposed to the chamber. Animals from the first group received HFS in their home cages before being submitted to conditioning; animals from the second group were first submitted to conditioning before receiving HFS during reexposure to the conditioning chamber; animals from the third group were submitted to the same regimen as those from the second group, except that no FS was delivered in the conditioning chamber; and animals from the fourth group received FS in the conditioning chamber but were maintained in their home cages the day after for LTP induction. Before conditioning, animals from the first group, placed in a familiar context (home cage), displayed an LTP of the N3 wave of septal field potential. After conditioning, reexposure of these animals to the conditioning chamber produced a transient decrease in the amplitude of N3 but did not interfere with the duration of maintenance of LTP. Conversely, in animals from the second group, when HFS was applied during reexposure to the conditioning chamber the induction of LTP was totally blocked. However, mice from the two other groups (3rd and 4th) displayed normal levels of LTP. Taken together with previous findings, these data suggest that contextual conditioned fear may interfere with certain forms of learning via blockade of hippocampal-septal LTP.
Rapidly Deactivating AMPA Receptors Determine Excitatory Synaptic Transmission to Interneurons in the Nucleus Tractus Solitarius From Rat
Authors: Titz Stefan , Keller Bernhard U.
Published: December 2017

Titz, Stefan and Bernhard U. Keller. Rapidly deactivating AMPA receptors determine excitatory synaptic transmission to interneurons in the nucleus tractus solitarius from rat. J. Neurophysiol. 78: 82–91, 1997. Excitatory synaptic transmission was investigated in interneurons of the parvocellular nucleus tractus solitarius (pNTS) by performing patch-clamp experiments in thin slice preparations from rat brain stem. Stimulation of single afferent fibers evoked excitatory postsynaptic currents (EPSCs) mediated by glutamate receptors of the dl-α-amino-3-hydroxy-5-methylisoxazole-propionic acid (AMPA) and N-methyl-d-aspartate types. AMPA-receptor-mediated EPSCs displayed decay time constants of 3.5 ± 1.2 (SD) ms (13 cells), which were slow compared with EPSC decay time constants in neurons of the cerebellum or hippocampus. Slow EPSC decay was not explained by dendritic filtering, because the passive membrane properties of pNTS interneurons provided favorable voltage-clamp conditions. Also, the slowness of EPSC decay did not result from slow deactivation of AMPA receptors (0.7 ± 0.2 ms, 5 cells), which was investigated during rapid application of agonist to outside-out patches. Comparison of AMPA receptor kinetics with EPSC decay time constants suggested that the slow time course of EPSCs resulted from the prolonged presence of glutamate in the synaptic cleft.
Passive Properties of Swimmeret Motor Neurons
Authors: Sherff Carolyn M. , Mulloney Brian
Published: December 2017

Sherff, Carolyn M. and Brian Mulloney. Passive properties of swimmeret motor neurons. J. Neurophysiol. 78: 92–102, 1997. Four different functional types of motor neurons innervate each swimmeret: return-stroke excitors (RSEs), power-stroke excitors (PSEs), return-stroke inhibitors (RSIs), and power-stroke inhibitors (PSIs). We studied the structures and passive electrical properties of these neurons, and tested the hypothesis that different types of motor neurons would have different passive properties that influenced generation of the swimmeret motor pattern. Cell bodies of neurons innervating one swimmeret were clustered in two anatomic groups in the same ganglion. The shapes of motor neurons in both groups were similar, despite the differences in locations of their cell bodies and in their functions. Diameters of their axons in the swimmeret nerve ranged from <2 to ∼35 μm. Resting membrane potentials, input resistances, and membrane time constants were recorded with microelectrodes in the processes of swimmeret motor neurons in isolated abdominal nerve cord preparations. Membrane potentials had a median of −59 mV, with 25th and 75th percentiles of −66.0 and −53 mV. The median input resistance was 6.4 MΩ, with 25th and 75th percentiles of 3.4 and 13.7 MΩ. Membrane time constants had a median of 9.3 ms, with 25th and 75th percentiles of 5.7 and 15.0 ms. Excitatory and inhibitory motor neurons had similar passive properties. RSE motor neurons were typically more depolarized than the other types, but the passive properties of RSE, PSE, RSI, and PSI neurons were not significantly different. Membrane time constants measured from cell bodies were briefer than those measured from neuropil processes, but membrane potentials and input resistances were not significantly different. The relative sizes of different motor neurons were measured from the sizes of their impulses recorded extracellularly from the swimmeret nerve. Smaller motor neurons had lower membrane potentials and were more likely to be active in the motor pattern than were large motor neurons. Motor neurons of different sizes had similar input resistances and membrane time constants. Motor neurons that were either oscillating or oscillating and firing in phase with the swimmeret motor pattern had lower average membrane potentials and longer time constants than those that were not oscillating. When the state of the swimmeret system changed from quiescence to continuous production of the motor pattern, the resting potentials, input resistances, and membrane time constants of individual swimmeret motor neurons changed only slightly. On average, both input resistance and membrane time constant increased. These similarities are considered in light of the functional task each motor neuron performs, and a hypothesis is developed that links the brief time constants of these neurons and graded synaptic transmission by premotor interneurons to control of the swimmeret muscles and the performance of the swimmeret system.
Effects of Kappa Opioid Receptor-Selective Agonists on Responses of Pelvic Nerve Afferents to Noxious Colorectal Distension
Authors: Su X. , Sengupta J. N. , Gebhart G. F.
Published: December 2017

Su, X., J. N. Sengupta, and G. F. Gebhart. Effects of kappa opiois receptor-selective agonists on responses of pelvic nerve afferents to noxious colorectal distension. J. Neurophysiol. 78: 1003–1012, 1997. The aim of this study was to examine the effects of κ-opioid receptor selective agonists on responses of mechanosensitive afferent fibers in the pelvic nerve. Single-fiber recordings were made from pelvic nerve afferents in the decentralized S1 dorsal root of the rat. A total of 572 afferent fibers in the S1 dorsal root were identified by electrical stimulation of the pelvic nerve; 252 (44%) responded to noxious colorectal distension (CRD; 80 mmHg). Of these 252 fibers that responded to CRD, 100 were studied further. All 100 fibers gave monotonic increases in firing to increasing pressures of CRD. Eighty-eight fibers had low thresholds for response (mean: 3 mmHg) and 12 fibers had high-thresholds for response (mean: 28 mmHg). Responses of 17 fibers also were tested after instillation of 5% mustard oil (MO) into the colon. The resting activity of 16/17 fibers significantly increased after MO instillation; 13 (77%) also exhibited sensitization of responses to graded CRD when tested 30 min after intracolonic MO instillation. The effects of κ1-opioid receptor preferring agonists (U50,488H, U69,593 and U62,066), the κ2-opioid receptor preferring agonist bremazocine, and the κ3-opioid receptor preferring agonist naloxone benzoylhydrazone (nalBzoH) were tested on responses of 64 mechanosensitive afferent fibers to noxious CRD. All five agonists dose-dependently inhibited afferent fiber responses to noxious CRD. Doses producing inhibition to 50% of the control response to CRD did not differ among the five agonists, ranging from ∼4 to 15 mg/kg. The effects of κ1, κ2, and κ3receptor agonists were attenuated by naloxone; two κ-opioid receptor-selective antagonists were ineffective. There were no differences in the dose-response relationships of these drugs for fibers recorded from untreated and irritant-treated colons. Conduction velocities of the fibers remained unaffected after high doses of all tested agonists. In an in vitro study, U50,488 (10−4M) did not produce any significant change in the tension of colonic smooth muscle. These results document that responses of mechanosensitive pelvic nerve afferent fibers innervating the colon are inhibited by κ-opioid receptor agonists having varying affinities for putative κ-opioid receptor subtypes. The inhibitory effects of these drugs likely are mediated by an action at receptors associated with the afferent fibers. The receptor at which these effects are produced is κ-opioid-like but clearly different from the κ-opioid receptor characterized in the CNS and is perhaps an orphan receptor.
A-Type K+ Current in Neurons Cultured From Neonatal Rat Hypothalamus and Brain Stem: Modulation by Angiotensin II
Authors: Wang Desuo , Sumners Colin , Posner Philip , Gelband Craig H.
Published: December 2017

Wang, Desuo, Colin Sumners, Philip Posner, and Craig H. Gelband. A-type K+ current in neurons cultured from neonatal rat hypothalamus and brain stem: modulation by angiotensin II. J. Neurophysiol. 78: 1021–1029, 1997. The regulation of A-type K+ current ( I A) and the single channel underlying I A in neonatal rat hypothalamus/brain stem cultured neurons were studied with the use of the patch-clamp technique. I A had a threshold of activation between −30 and −25 mV ( n = 14). Steady-state inactivation of I A occurred between −80 and −70 mV and had a membrane voltage at which I A was half-maximum of −52.2 mV ( n = 14). The mean values for the activation and inactivation (decay) time constants during a voltage step to +20 mV were 2.1 ± 0.3 (SE) ms ( n = 8) and 13.6 ± 1.9 ms ( n = 8), respectively. Single-channel recordings from outside-out patches revealed A-type K+ channels with voltage-dependent activation, 4-aminopyridine (4-AP) sensitivity, and inactivation kinetics similar to those of I A. The single-channel conductance obtained from cell-attached patches was15.8 ± 1.3 pS ( n = 4) in a physiological K+ gradient and 41.2 ± 3.7 pS ( n = 5) in symmetrical 140 mM K+. Angiotensin II (Ang II, 100 nM) reduced peak I A by ∼20% during a voltage step to +20 mV ( n = 8). Similarly, Ang II (100 nM) markedly reduced single A-type K+ channel activity by decreasing open probability ( n = 4). The actions of Ang II on I A and single A-type K+ channels were reversible either by addition of the selective angiotensin type 1 (AT1) receptor antagonist losartan (1 μM) or on washout of the peptide. Thus the activation of AT1 receptors inhibits a tetraethylammonium-chloride-resistant, 4-AP-sensitive I A and single A-type K+ channels, and this may underlie some of the actions of Ang II on electrical activity of the brain.
Hyperexcitability in Combined Entorhinal/Hippocampal Slices of Adult Rat After Exposure to Brain-Derived Neurotrophic Factor
Authors: Scharfman Helen E.
Published: December 2017

Scharfman, Helen E. Hyperexcitability in combined entorhinal/hippocampal slices of adult rat after exposure to brain-derived neurotrophic factor. J. Neurophysiol. 78: 1082–1095, 1997. Effects of brain-derived neurotrophic factor (BDNF) in area CA3, the dentate gyrus, and medial entorhinal cortex were examined electrophysiologically by bath application of BDNF in slices containing the hippocampus and entorhinal cortex. Bath application of 25–100 ng/ml BDNF for 30–90 min increased responses to single afferent stimuli in selective pathways in the majority of slices. In area CA3, responses to mossy fiber stimulation increased in 73% of slices and entorhinal cortex responses to white matter stimulation increased in 64% of slices. After exposure to BDNF, these areas also demonstrated evidence of hyperexcitability, because responses to repetitive stimulation (1-Hz paired pulses for several s) produced multiple population spikes in response to mossy fiber stimulation in CA3 or multiple field potentials in response to white matter stimulation in the entorhinal cortex. Repetitive field potentials persisted after repetitive stimulation ended and usually were followed by spreading depression. Enhancement of responses to single stimuli and hyperexcitability were never evoked in untreated slices or after bath application of boiled BDNF or cytochrome C. The tyrosine kinase antagonist K252a (2 μM) blocked the effects of BDNF. In area CA3, both the potentiation of responses to single stimuli and hyperexcitability showed afferent specificity, because responses to mossy fiber stimulation were affected but responses to fimbria or Schaffer collateral stimulation were not. In addition, regional specificity was demonstrated in that the dentate gyrus was much less affected. The effects of BDNF in area CA3 were similar to those produced by bath application of low doses of kainic acid, which is thought to modulate glutamate release from mossy fiber terminals by a presynaptic action. These results suggest that BDNF has acute effects on excitability in different areas of the hippocampal-entorhinal circuit. These effects appear to be greatest in areas that are highly immunoreactive for BDNF, such as the mossy fibers and the entorhinal cortex. Although the present experiments do not elucidate mechanism(s) definitively, the afferent specificity, similarity to the effects of kainic acid, and block by K252a are consistent with previous hypotheses that BDNF affects acute excitability by a presynaptic action on trkB receptors that modulate excitatory amino acid transmission. However, we cannot rule out actions on inhibitory synapses or postsynaptic processes.
Systematic Changes in Directional Tuning of Motor Cortex Cell Activity With Hand Location in the Workspace During Generation of Static Isometric Forces in Constant Spatial Directions
Authors: Sergio Lauren E. , Kalaska John F.
Published: December 2017

Sergio, Lauren E. and John F. Kalaska. Systematic changes in directional tuning of motor cortex cell activity with hand location in the workspace during generation of static isometric forces in constant spatial directions. J. Neurophysiol. 78: 1170–1174, 1997. We examined the activity of 46 proximal-arm-related cells in the primary motor cortex (MI) during a task in which a monkey uses the arm to exert isometric forces at the hand in constant spatial directions while the hand is in one of nine different spatial locations on a plane. The discharge rate of all 46 cells was significantly affected by both hand location and by the direction of static force during the final static-force phase of the task. In addition, all cells showed a significant interaction between force direction and hand location. That is, there was a significant modulation in the relationship between cell activity and the direction of exerted force as a function of hand location. For many cells, this modulation was expressed in part as a systematic arclike shift in the cell's directional tuning at the different hand locations, even though the direction of static force output at the hand remained constant. These effects of hand location in the workspace indicate that the discharge of single MI cells does not covary exclusively with the level and direction of force output at the hand. Sixteen proximal-arm-related muscles showed similar effects in the task, reflecting their dependence on various mechanical factors that varied with hand location. The parallel changes found for both MI cell activity and muscle activity for static force production at different hand locations are further evidence that MI contributes to the transformation between extrinsic and intrinsic representations of limb movement.
Contribution of Vestibular Commissural Pathways to Spatial Orientation of the Angular Vestibuloocular Reflex
Authors: Wearne Susan , Raphan Theodore , Cohen Bernard
Published: December 2017

Wearne, Susan, Theodore Raphan, and Bernard Cohen. Contribution of vestibular commissural pathways to spatial orientation of the angular vestibuloocular reflex. J. Neurophysiol. 78: 1193–1197, 1997. During nystagmus induced by the angular vestibuloocular reflex (aVOR), the axis of eye velocity tends to align with the direction of gravitoinertial acceleration (GIA), a process we term “spatial orientation of the aVOR.” We studied spatial orientation of the aVOR in rhesus and cynomolgus monkeys before and after midline section of the rostral medulla abolished all oculomotor functions related to velocity storage, leaving the direct optokinetic and vestibular pathways intact. Optokinetic afternystagmus and the bias component of off-vertical-axis rotation were lost, and the aVOR time constant was reduced to a value commensurate with the time constants of primary semicircular canal afferents. Spatial orientation of the aVOR, induced either during optokinetic or vestibular stimulation, was also lost. Vertical and roll aVOR time constants could no longer be lengthened in side-down or supine/prone positions, and static and dynamic tilts of the GIA no longer produced cross-coupling from the yaw to pitch and yaw to roll axes. Consequently, the induced nystagmus remained entirely in head coordinates after the lesion, regardless of the direction of the resultant GIA vector. Gains of the aVOR and of optokinetic nystagmus to steps of velocity were unaffected or slightly increased. These results are consistent with a model in which the direct aVOR pathways are organized in semicircular canal coordinates and spatial orientation is restricted to the indirect (velocity storage) pathways.
Response Properties of Neurons in the Inferior Colliculus of the Monaurally Deafened Ferret to Acoustic Stimulation of the Intact Ear
Authors: McAlpine David , Martin Russell L. , Mossop Jennifer E. , Moore David R.
Published: December 2017

McAlpine, David, Russell L. Martin, Jennifer E. Mossop, and David R. Moore. Response properties of neurons in the inferior colliculus of the monaurally deafened ferret to acoustic stimulation of the intact ear. J. Neurophysiol. 78: 767–779, 1997. Response properties of neurons in the central nucleus of the inferior colliculus (ICC) were investigated after unilateral cochlear removal at various ages during infancy. Nineteen ferrets had the right cochlea surgically ablated, either in adulthood or on postnatal day (P) 5, 25, or 40, 3–18 mo before recording. Adult ablations were made on the same day as (“acute,” n = 3), or 2–3 mo before (“chronic,” n = 3), recording. Two ferrets were left binaurally intact. Single-unit ( n = 702) and multiunit ( n = 1,819) recordings were made in the ICC of barbiturate-anesthetized ferrets ipsilateral (all ages) or contralateral (P5 and acute adult only) to the intact ear. In binaurally intact animals, tonal stimulation of the contralateral ear evoked excitatory activity at the majority (94%) of recording loci, whereas stimulation of the ipsilateral ear evoked activity at only 33% of recording loci. In acutely ablated animals, the majority of contralateral (90%) and ipsilateral (70%) loci were excited by tonal stimulation of the intact ear. In chronically ablated animals, 80–90% of loci were excited by ipsilateral stimulation. Single-unit thresholds were generally higher for low-best frequency (BF) than for high-BF units, and higher in the ipsilateral than in the contralateral ICC. Analysis of covariance showed highly significant differences between all of the ipsilateral and contralateral groups, but no effects of age at ablation or survival time following ablation, other than that the group ablated at P25 had higher mean ipsilateral thresholds than the groups ablated at P5 or, acutely, in adulthood. Cochlear ablation at P5, 25, or 40 resulted in a significant increase in dynamic ranges of ipsilateral ICC unit rate-intensity functions relative to acutely ablated animals. Dynamic ranges of units in the contralateral ICC of P5-ablated ferrets were also significantly increased compared with those of acutely ablated animals. Cochlear ablation at P5, 25, or 40 resulted in a significant increase in single-unit spontaneous discharge rates in the ICC ipsilateral but not contralateral (P5 only) to the intact ear. These data show that unilateral cochlear removal in adult ferrets leads to a rapid and dramatic increase in the proportion of neurons in the ICC ipsilateral to the intact ear that is excited by acoustic stimulation of that ear. In addition, the data confirm that, in ferrets, cochlear removal in infancy leads to a further increase in responsiveness of individual neurons in the ipsilateral ICC. Finally, the data show that responses in the ICC contralateral to the intact ear are largely but not completely unchanged by unilateral cochlear removal.