bluuebunny/crossref_metadata_2025 huggingface dataset:
Two Types of ACh Receptors Contribute to Fast Channel Gating on Mouse Skeletal Muscle
Authors: Shepherd Dawn , Brehm Paul
Published: December 2017

Shepherd, Dawn and Paul Brehm. Two types of ACh receptors contribute to fast channel gating on mouse skeletal muscle. J. Neurophysiol. 78: 2966–2974, 1997. Single-channel recordings from mouse C2 myotubes indicate that maturation of skeletal muscle is accompanied by the appearance of two types of fast acetylcholine (ACh) receptor channels that are each functionally distinct from the embryonic receptor type present at early stages of differentiation. The embryonic receptor type has a low conductance (45 pS) and long channel open time, rendering slowly decaying synaptic currents. One fast channel type that appears during muscle maturation is distinguished from the embryonic receptor type on the basis of both higher conductance (65 pS) and shorter open time. However, single-channel recordings from differentiated mouse skeletal muscle cell line (C2) point to the existence of a second fast receptor type, which has a conductance similar to the embryonic receptor type (45 pS), yet significantly reduced mean channel open time. Analyses of individual channel function at high ACh concentrations directly demonstrate the coexistence of two kinetically distinct types of 45 pS ACh receptors. Openings by fast type and slow embryonic type of 45 pS receptors occurred in bursts, allowing distinction on the basis of both mean open time and open probability for individual receptors. The embryonic type of 45 pS receptor has an open time approximately twofold longer than the fast-receptor counterpart. Additional differences were reflected in the open probability distributions for fast and slow 45 pS receptor types. Both types of 45 pS receptor were kinetically distinguishable from the 65 pS receptor. We found no support for the idea that the slow and fast 45 pS receptor types result from the interconversion of dual gating modes involving the same receptor protein. Our results are consistent with the idea that the acquisition of fast synaptic current decay, required at mature neuromuscular synapses, is the result of the up-regulation of two distinct fast types of nicotinic ACh receptors during skeletal muscle development.
Stretch of Quadriceps Inhibits the Soleus H Reflex During Locomotion in Decerebrate Cats
Authors: Misiaszek John E. , Pearson Keir G.
Published: December 2017

Misiaszek, John E. and Keir G. Pearson. Stretch of quadriceps inhibits the soleus H reflex during locomotion in decerebrate cats. J. Neurophysiol. 78: 2975–2984, 1997. Previously, it has been demonstrated that afferent signals from the quadriceps muscles can suppress H reflexes in humans during passive movements of the leg. To establish whether afferent input from quadriceps contributes to the modulation of the soleus H reflex during locomotion, the soleus H reflex was conditioned with stretches of the quadriceps muscle during bouts of spontaneous treadmill locomotion in decerebrate cats. We hypothesized that 1) in the absence of locomotion such conditioning would lead to suppression of the soleus H reflex and 2) this would be retained during periods of locomotor activity. In the absence of locomotion, slow sinusoidal stretches (0.2 Hz, 8 mm) of quadriceps cyclically modulated the amplitude of the soleus H reflex. The H reflex amplitude was least during the lengthening of the quadriceps and greatest as quadriceps shortened. Further, low-amplitude vibrations (48–78 μm) applied to the patellar tendon suppressed the reflex, indicating that the muscle spindle primaries were the receptor eliciting the effect. During bouts of locomotion, ramp stretches of quadriceps were applied during the extensor phase of the locomotor rhythm. Soleus H reflexes sampled at two points during the stance phase were reduced compared with phase-matched controls. The background level of the soleus electromyographic activity was not influenced by the applied stretches to quadriceps, either during locomotion or in the absence of locomotion. This indicates that the excitability of the soleus motoneuron pool was not influenced by the stretching of quadriceps, and that the inhibition of the soleus H reflex is due to presynaptic inhibition. We conclude that group Ia afferent feedback from quadriceps contributes to the regulation of the soleus H reflex during the stance phase of locomotion in decerebrate cats. This afferent mediated source of regulation of the H reflex, or monosynaptic stretch reflex, would allow for rapid alterations in reflex gain according to the dynamic needs of the animal. During early stance, this source of regulation might suppress the soleus stretch reflex to allow adequate yielding at the ankle and facilitate the movement of the body over the foot.
Somatostatin Depresses Excitatory but not Inhibitory Neurotransmission in Rat CA1 Hippocampus
Authors: Tallent Melanie K. , Siggins George R.
Published: December 2017

Tallent, Melanie K. and George R. Siggins. Somatostatin depresses excitatory but not inhibitory neurotransmission in rat CA1 hippocampus. J. Neurophysiol. 78: 3008–3018, 1997. In rat CA1 hippocampal pyramidal neurons (HPNs), somatostatin (SST) has inhibitory postsynaptic actions, including hyperpolarization of the membrane at rest and augmentation of the K+ M-current. However, the effects of SST on synaptic transmission in this brain region have not been well-characterized. Therefore we used intracellular voltage-clamp recordings in rat hippocampal slices to assess the effects of SST on pharmacologically isolated synaptic currents in HPNs. SST depressed both (R,S)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate and N-methyl-d-aspartate (NMDA) receptor-mediated excitatory postsynaptic currents (EPSCs) in a reversible manner, with an apparent IC50 of 22 nM and a maximal effect at 100 nM. In contrast, SST at concentrations up to 5 μM had no direct effects on either γ-aminobutyric acid-A (GABAA) or GABAB receptor–mediated inhibitory postsynaptic currents (IPSCs). The depression of EPSCs by SST was especially robust during hyperexcited states when polysynaptic EPSCs were present, suggesting that this peptide could play a compensatory role during seizurelike activity. SST effects were greatly attenuated by the alkylating agent N-ethylmaleimide, thus implicating a transduction mechanism involving the Gi/Go family of G-proteins. Use of 2 M Cs+ in the recording electrode blocked the postsynaptic modulation of K+ currents by SST, but did not alter the effects of SST on EPSCs, indicating that postsynaptic K+ currents are not involved in this action of SST. However, 2 mM external Ba2+ blocked the effect of SST on EPSCs, suggesting that presynaptic K+ channels or other presynaptic mechanisms may be involved. These findings and previous results from our laboratory show that SST has multiple inhibitory effects in hippocampus.
Heterogeneous Voltage Dependence of Inward Rectifier Currents in Spiral Ganglion Neurons
Authors: Mo Zun-Li , Davis Robin L.
Published: December 2017

Mo, Zun-Li and Robin L. Davis. Heterogeneous voltage dependence of inward rectifier currents in spiral ganglion neurons. J. Neurophysiol. 78: 3019–3027, 1997. Inward rectification was characterized in neonatal spiral ganglion neurons maintained in tissue culture. Whole cell current and voltage-clamp techniques were used to show that the hyperpolarization-activated cationic ( I h) current underlies most or all of the inward rectification demonstrated in these neurons. The average reversal potential (−41.3 mV) and cesium sensitivity were typical of that found in other neurons and cell types. What was unique about the hyperpolarization-activated currents, however, was that the half-maximal voltages ( V 1/2) and slope factors ( k) that characterized I h current activation were graded from neuron to neuron. Voltage-clamp recordings made with standard bath and pipette solutions revealed V 1/2 values that ranged from −78.1 to −122.1 mV, with slope factors from 7.6 to 13.1. These gradations in the voltage-dependent features of the I h current did not result from variability in the recording conditions because independently measured Na+ current-to-voltage relationships were found to be uniform (peak current at −20 mV). Moreover, the range and average V 1/2 and slope values could be altered with activators [8-(4-chlorophenylthio) adenosine 3′,5′-cyclic monophosphate in combination with okadaic acid] or inhibitors { N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide}of protein indicating that I h current heterogeneity most likely resulted from differential phosphorylation.
Recurrent Inhibitory Interneurons of the Rabbit's Lateral Posterior-Pulvinar Complex
Authors: Zhu J. Julius , Lo Fu-Sun
Published: December 2017

Zhu, J. Julius and Fu-Sun Lo. Recurrent inhibitory interneurons of the rabbit's lateral posterior-pulvinar complex. J. Neurophysiol. 78: 3117–3124, 1997. We recorded from 118 neurons in the visual sector of the thalamic reticular nucleus (TRN) in anesthetized rabbits. Cells were identified by their location and characteristic burst responses to stimulation of the primary visual cortex (Cx) and optic chiasm (OX) and were classified into two groups. Type I cells had relatively short latencies from both OX and Cx stimulation, and the latency from OX was always longer than from Cx. In contrast, type II cells had much longer latencies after OX and Cx stimulation, and the latency from OX was always shorter than from Cx. Type I cells were located in the dorsal part of TRN, whereas type II cells were located in the ventral part of TRN. The physiological properties and location of type I TRN cells indicate that they are recurrent inhibitory interneurons of the dorsal lateral geniculate nucleus (LGN). Type II TRN cells most likely function as recurrent inhibitory interneurons for the lateral posterior nucleus-pulvinar complex (LP) because they could be activated antidromically by LP stimulation and orthodromically activated via axonal collaterals of LP cells. Type II TRN cells exhibited a prolonged depression after Cx or OX stimulation. Intracellular recordings showed that a prolonged inhibitory postsynaptic potential was evoked by Cx or OX stimulation. Therefore, these recurrent interneurons of LP, type II cells form mutual inhibitory connections just like those recurrent interneurons of LGN, type I cells. Our data suggest that the geniculocortical and extrageniculate visual pathways have similar recurrent inhibitory circuits.
Activation and Recovery of the PGE2-Mediated Sensitization of the Capsaicin Response in Rat Sensory Neurons
Authors: Lopshire J. C. , Nicol G. D.
Published: December 2017

Lopshire, J. C. and G. D. Nicol. Activation and recovery of the PGE2-mediated sensitization of the capsaicin response in rat sensory neurons. J. Neurophysiol. 78: 3154–3164, 1997. Pro-inflammatory prostaglandins are known to enhance the sensitivity of sensory neurons to various modalities of stimulation, including the excitatory chemical agent, capsaicin. In this report, we examined the capacity of prostaglandin E2 (PGE2) to enhance the capsaicin response recorded from sensory neurons isolated from embryonic rats and grown in culture. Previous work demonstrated that the cyclic adenosine 3′,5′-monophosphate pathway mediates initiation of the PGE2-induced sensitization, however, little is known about the pathways regulating the recovery from sensitization. Therefore, we examined the neuronal transduction cascades that control the duration of sensitization. Treatment with PGE2 enhanced the capsaicin-evoked current by two- to threefold, however, this sensitization was transient even in the continued presence of prostaglandin. The duration of sensitization produced by PGE2 was related inversely to the extracellular Ca2+ concentration with the shortest recovery times observed in cells exposed to 2 mM Ca2+-Ringer. Inclusion of the Ca2+ chelator, bis-( o-aminophenoxy)- N,N,N′,N′-tetraacetic acid, in the recording pipette greatly lengthened the period of sensitization. Pretreatment with either the nitric oxide synthase inhibitor, nitro-L-arginine methyl ester (L-NAME), or the inhibitor of the cyclic guanosine 3′,5′-monophosphate (GMP)–dependent protein kinase, KT-5823, before the application of PGE2 increased the duration of sensitization even in the presence of 2 mM Ca2+. In contrast, after attaining maximal sensitization in 2 mM Ca2+-Ringer containing L-NAME, the addition of either nitric oxide donors (3-morpholinosydnonimine or s-nitroso-n-acetylpenicillamine) or 8-Br-cyclic GMP led to a rapid decrease in the level of sensitization. In the absence of sensitization, nitric oxide-cyclic GMP modulating agents had no effect on the capsaicin-evoked current. Therefore, these results suggest that capsaicin-induced elevations in intracellular Ca2+ levels lead to an enhanced production of cyclic GMP, via the nitric oxide pathway, that ultimately activates cyclic GMP-dependent protein kinase. This protein kinase inactivates or terminates the sensitization produced by PGE2 by an as yet unidentified mechanism.
Glutamate Microstimulation of Local Inhibitory Circuits in the Supraoptic Nucleus From Rat Hypothalamus Slices
Authors: Wuarin Jean-Pierre
Published: December 2017

Wuarin, Jean-Pierre. Glutamate microstimulation of local inhibitory circuits in the supraoptic nucleus from rat hypothalamus slices. J. Neurophysiol. 78: 3180–3186, 1997. The hypothesis of a local inhibitory input to the hypothalamic supraoptic nucleus was tested with combined glutamate microstimulation and whole cell patch-clamp recordings in slices from rat hypothalamus. Synaptic activity in supraoptic magnocellular neuroendocrine cells (MNCs) was monitored and glutamate microdrops were applied in the perinuclear region of the supraoptic nucleus to evoke firing of action potentials in putative presynaptic inhibitory cells. The effect of glutamate microdrops applied in the perinuclear region was tested on 57 supraoptic MNCs. In control conditions, spontaneous excitatory (EPSCs) and inhibitory (IPSCs) postsynaptic currents were observed at resting membrane potential in all MNCs tested. Glutamate microstimulation evoked an abrupt increase in the frequency and size of spontaneous IPSCs in eight MNCs. Forty-nine MNCs did not show any change in the inhibitory synaptic input. Microapplication of glutamate in the periphery of the supraoptic nucleus did not modify the amplitude or the frequency of spontaneous EPSCs in any of the 57 MNCs tested. In the group of eight MNCs that responded to glutamate microstimulation by an increase in inhibitory input, two types of responses were observed. Four MNCs showed an increase in both size and frequency of spontaneous IPSCs through the entire range of amplitude. In the other four MNCs, local glutamate stimulation produced a dramatic increase in the size of IPSCs and a lesser increase in the frequency of the smaller IPSCs. The potential effect of the glutamate-evoked increase in inhibitory input on the firing activity of MNCs was tested in current-clamp conditions. Intracellular current injection was applied to evoke firing of action potentials in six MNCs that had responded to local glutamate microstimulation by an increase in inhibitory input. Glutamate microdrop applications inhibited the evoked action potential firing in all six cells. These results suggest 1) that local inhibitory interneurons are present in the periphery of the supraoptic nucleus, 2) that they contain functional glutamate receptors, 3) that they form inhibitory synapses with supraoptic MNCs, and 4) that activation of these interneurons inhibits firing in MNCs. These results support the hypothesis that local inhibitory interneurons play a important role in the firing activity of supraoptic MNCs.
Experimental and Modeling Study of Na+Current Heterogeneity in Rat Nodose Neurons and Its Impact on Neuronal Discharge
Authors: Schild J. H. , Kunze D. L.
Published: December 2017

Schild, J. H. and D. L. Kunze. Experimental and modeling study of Na+current heterogeneity in rat nodose neurons and its impact on neuronal discharge. J. Neurophysiol. 78: 3198–3209, 1997. This paper is a combined experimental and modeling study of two fundamental questions surrounding the functional characteristics of Na+currents in nodose sensory neurons. First, when distinctly different classes of Na+currents are expressed in the same neuron, is there a significant difference in the intrinsic biological variability associated with the voltage- and time-dependent properties of these currents? Second, in what manner can such variability in functional properties impact the discharge characteristics of these neurons? Here, we recorded the whole cell Na+currents in acutely dissociated rat nodose sensory neurons using the patch-clamp technique. Two general populations of neurons were observed. A-type neurons ( n = 20) expressed a single rapidly inactivating tetrodotoxin-sensitive (TTX-S) Na+current. C-type neurons ( n = 87) coexpressed this TTX-S current along with a slowly inactivating TTX-resistant (TTX-R) Na+current. The TTX-S currents in both cell types had submillisecond rates of activation at room temperature with thresholds near −50 mV. The TTX-R current exhibited about the same rates of activation but required potentials 20–30 mV more depolarized to reach threshold. Over the same clamp voltages the rates of inactivation for the TTX-R current were three to nine times slower than those for the TTX-S current. However, the TTX-R current recovered from complete inactivation at a rate 10–20 times faster than the TTX-S current (10 ms as compared with 100–200 ms). Across the population of neurons studied the TTX-S data formed a relatively tight statistical distribution, exhibiting low standard deviations across all measured voltage- and time-dependent properties. In contrast, the same pooled measurements on the TTX-R data exhibited standard deviations that were 3–10 times larger. The statistical profiles of the voltage- and time-dependent properties of these currents then were used as a physiological guide to adjust the relevant parameters of a mathematical model of nodose sensory neurons previously developed by our group ( Schild et al. 1994 ). Here, we show how the relative expression of TTX-S and TTX-R Na+currents and the differences in their apparent biological variability can shape the regenerative discharge characteristics and action potential waveshapes of sensory neurons. We propose that the spectrum of variability robust reactivation characteristics of the TTX-R current are important determinants in establishing the heterogeneous stimulus-response characteristics often observed across the general population of C-type sensory neurons.
Analysis of Primate IBN Spike Trains Using System Identification Techniques. II. Relationship to Gaze, Eye, and Head Movement Dynamics During Head-Free Gaze Shifts
Authors: Cullen Kathleen E. , Guitton Daniel
Published: December 2017

Cullen, Kathleen E. and Daniel Guitton. Analysis of primate IBN spike trains using system identification techniques. II. Relationship to gaze, eye, and head movement dynamics during head-free gaze shifts. J. Neurophysiol. 78: 3283–3306, 1997. We have investigated the relationships among the firing frequency B( t) of inhibitory burst neurons (IBNs) and the metrics and dynamics of the eye, head, and gaze (eye + head) movements generated during voluntary combined eye-head gaze shifts in monkey. The same IBNs were characterized during head-fixed saccades in our first of three companion papers. In head-free gaze shifts, the number of spikes (NOS) in a burst was, for 82% of the neurons, better correlated with gaze amplitude than with the amplitude of either the eye or head components of the gaze shift. A multiple regression analysis confirmed that NOS was well correlated to the sum of head and eye amplitudes during head-free gaze shifts. Furthermore, the mean slope of the relationship between NOS and gaze amplitude was significantly less for head-free gaze shifts than for head-fixed saccades. NOS is a global parameter. To refine we used system identification techniques to evaluate a series of dynamic models in which IBN spike trains were related to gaze or eye movements. We found that gaze- and eye-based models predicted the discharges of IBNs equally well. However, the bias values required by gaze-based models were comparable to those required in our head-fixed models whereas those required by eye-based models were significantly larger. The difference in biases between gaze- and eye-based models was very strongly correlated to the mean head velocity ( H˙) during gaze shifts [ R = −0.93 ± 0.15 (SD)]. This result suggested that the increased bias required by the eye-based models reflected an unmodeled H˙ input onto these cells. To pursue this argument further we investigated a series of dynamic models that included both eye velocity ( E˙) and H˙ terms and this confirmed the importance of these two terms. As in our head-fixed analysis of companion paper I, the most valuable model formulation also included an eye saccade amplitude term (Δ E) and was given by B( t) = r 0 + r 1Δ E + b 1 E˙ + g 1 H˙ where r 0, r 1, b 1, and g 1 are constants. The amplitude of the head velocity coefficient was significantly less than that of the eye velocity coefficient. Furthermore, in our population long-lead IBNs tended to have a smaller head velocity coefficients than short-lead IBNs. We conclude that during head-free gaze shifts, the head velocity signal carried to the abducens nucleus by primate excitatory burst neurons (EBNs; if EBNs and IBNs carry similar signals) must be offset by other premotor cells.
Behavioral Function of Glutamatergic Interneurons in the Feeding System ofLymnaea: Plateauing Properties and Synaptic Connections with Motor Neurons
Authors: Brierley Matthew J. , Staras Kevin , Benjamin Paul R.
Published: December 2017

Brierley, Matthew J., Kevin Staras, and Paul R. Benjamin. Behavioral function of glutamatergic interneurons in the feeding system of Lymnaea: plateauing properties and synaptic connections with motor neurons. J. Neurophysiol. 78: 3386–3395, 1997. Intracellular recording techniques were used to examine the electrical properties and behavioral function of a novel type of retraction phase interneuron, the N2 ventral (N2v) cells in the feeding network of the snail Lymnaea. The N2vs were compared with the previously identified N2 cells that now are renamed the N2 dorsal (N2d) cells. The N2vs are a bilaterally symmetrical pair of electrotonically coupled plateauing interneurons that are located on the ventral surfaces of the buccal ganglia. Their main axons project to the opposite buccal ganglion, but they have an additional fine process in the postbuccal nerve. N2v plateaus that outlast the duration of the stimulus can be triggered by depolarizing current pulses and prematurely terminated by applied hyperpolarizing pulses. Gradually increasing the amplitude of depolarizing pulses reveals a clear threshold for plateau initiation. N2v plateauing persists in a high Mg2+/nominally zero Ca2+saline that blocks chemical synaptic connections, suggesting an endogenous mechanism for plateau generation. The N2vs fire sustained bursts of action potentials throughout the N2/rasp phase of the fictive feeding cycle and control the retraction phase feeding motor neurons. The N2vs excite the B3 and B9 feeding motor neurons to fire during the rasp phase of the feeding cycle. They also inhibit the B7 and B8 feeding motor neurons. The B8 cells recover from inhibition and fire during the following swallowing phase. These synaptic connections appear to be monosynaptic as they persist in high Mg2+/high Ca2+(HiDi) saline that blocks polysynaptic pathways. Strong current-induced plateaus in the N2vs generate brief inhibitory postsynaptic responses in the B4CL rasp phase motor neurons, but this was due to the indirect N2v → N2d → B4CL pathway. The N2vs are coupled electrotonically to the N2d cells, and triggering plateau in a N2v usually induced one or two spikes in a N2d. Previous experiments showed that the N2ds generate plateau potentials during a fictive feeding cycle. Here we show that the main component of the “plateauing” waveform is due to the electrotonic coupling with the N2v cells. The differential synaptic connections of the N2v and N2d cells with retraction phase motor neurons results in a sequence of motor neuron burst activity B9 → B4CL → B8 that produces the full retraction (rasp → swallow) movements of the feeding apparatus (buccal mass). We conclude that the N2v cells are an essential component of the interneuronal network required to produce feeding motor neuron activity.
Behavior-Dependent Activities of a Central Pattern Generator in Freely BehavingLymnaea stagnalis
Authors: Jansen Rene F. , Pieneman Anton W. , ter Maat Andries
Published: December 2017

Jansen, Rene F., Anton W. Pieneman, and Andries ter Maat. Behavior-dependent activities of a central pattern generator in freely behaving Lymnaea stagnalis. J. Neurophysiol. 78: 3415–3427, 1997. Cyclic or repeated movements are thought to be driven by networks of neurons (central pattern generators) that are dynamic in their connectivity. During two unrelated behaviors (feeding and egg laying), we investigated the behavioral output of the buccal pattern generator as well as the electrical activity of a pair of identified interneurons that have been shown to be involved in setting the level of activity of this pattern generator (PG). Analysis of the quantile plots of the parameters that describe the behavior (movements of the buccal mass) reveals that during egg laying, the behavioral output of the PG is different compared with that during feeding. Comparison of the average durations of the different parts of the buccal movements showed that during egg laying, the duration of one specific part of buccal movement is increased. Correlated with these changes in the behavioral output of the PG were changes in the firing rate of the cerebral giant neurons (CGC), a pair of interneurons that have been shown to modulate the activity of the PG by means of multiple synaptic contacts with neurons in the buccal ganglion. Interval- and autocorrelation histograms of the behavioral output and CGC spiking show that both the PG output and the spiking properties of the CGCs are different when comparing egg-laying animals with feeding animals. Analysis of the timing relations between the CGCs and the behavioral output of the PG showed that both during feeding and egg laying, the electrical activity of the CGCs is largely in phase with the PG output, although small changes occur. We discuss how these results lead to specific predictions about the kinds of changes that are likely to occur when the animal switches the PG from feeding to egg laying and how the hormones that cause egg laying are likely to be involved.
Inhibition of Dendritic Calcium Influx by Activation of G-Protein–Coupled Receptors in the Hippocampus
Authors: Chen Huanmian , Lambert Nevin A.
Published: December 2017

Chen, Huanmian and Nevin A. Lambert. Inhibition of dendritic calcium influx by activation of G-protein–coupled receptors in the hippocampus. J. Neurophysiol. 78: 3484–3488, 1997. Gi proteins inhibit voltage-gated calcium channels and activate inwardly rectifying K+ channels in hippocampal pyramidal neurons. The effect of activation of G-protein–coupled receptors on action potential-evoked calcium influx was examined in pyramidal neuron dendrites with optical and extracellular voltage recording. We tested the hypotheses that 1) activation of these receptors would inhibit calcium channels in dendrites; 2) hyperpolarization resulting from K+ channel activation would deinactivate low-threshold, T-type calcium channels on dendrites, increasing calcium influx mediated by these channels; and 3) activation of these receptors would inhibit propagation of action potentials into dendrites, and thus indirectly decrease calcium influx. Activation of adenosine receptors, which couple to Gi proteins, inhibited calcium influx in cell bodies and proximal dendrites without inhibiting action-potential propagation into the proximal dendrites. Inhibition of dendritic calcium influx was not changed in the presence of 50 μM nickel, which preferentially blocks T-type channels, suggesting influx through these channels is not increased by activation of G-proteins. Adenosine inhibited propagation of action potentials into the distal branches of pyramidal neuron dendrites, leading to a three- to fourfold greater inhibition of calcium influx in the distal dendrites than in the soma or proximal dendrites. These results suggest that voltage-gated calcium channels are inhibited in pyramidal neuron dendrites, as they are in cell bodies and terminals and thatG-protein–mediated inhibition of action-potential propagation can contribute substantially to inhibition of dendritic calcium influx.
Muscle Fibers in Regenerating Crayfish Motor Nerves
Authors: Pearce Joanne , Krause Kristin M. , Govind C. K.
Published: December 2017

Pearce, Joanne, Kristin M. Krause, and C. K. Govind. Muscle fibers in regenerating crayfish motor nerves. J. Neurophysiol. 78: 3498–3501, 1997. Single discrete muscle fibers were found in regenerating motor nerves in adult crayfish. The regenerating nerves were from native or transplanted ganglia in the third abdominal segments and consisted of several motor axons. The proximal end of these motor axons showed numerous sprouts. Muscle fibers in these regenerating nerves appeared newly developed and were innervated by excitatory nerve terminals. A likely source of these novel muscle fibers may be blood cells in the nerve or satellite cells from neighboring muscle. Contacts made by axon sprouts with other axon sprouts, glia, and muscle fiber, in the form of a dense bar with clustered clear vesicles, characterized the regenerating nerve. These contacts may provide a possible signaling pathway for axon regeneration and myogenesis.
Bidirectional Electrical Coupling Between Inspiratory Motoneurons in the Newborn Mouse Nucleus Ambiguus
Authors: Rekling Jens C. , Feldman Jack L.
Published: December 2017

Rekling, Jens C. and Jack L. Feldman. Bidirectional electrical coupling between inspiratory motoneurons in the newborn mouse nucleus ambiguus. J. Neurophysiol. 78: 3508–3510, 1997. Some spinal and brain stem motoneurons are electrically coupled in the early postnatal period. To test whether respiratory motoneurons in the brain stem are electrically coupled, we performed single and dual whole cell patch recordings from presumptive motoneurons in the nucleus ambiguus in a rhythmically active brain stem slice from newborn mice. Two of eight (25%) biocytin-injected neurons showed dye-coupling and 4 of 11 (36%) of intracellularly recorded pairs of neurons showed evidence of bidirectional electrical coupling. Impulse activity in one cell elicited small spikelets in the other and hyperpolarization of one cell led to hyperpolarization of the other with a coupling ratio (Δ V 2:Δ V 1) of 0.03–0.14. We conclude that inspiratory ambiguus motoneurons in the newborn mouse brain stem are bidirectionally electrically coupled, which may serve to transmit or coordinate signals, chemical or electrical.
Calcium-Activated Potassium Conductances in Retinal Ganglion Cells of the Ferret
Authors: Wang Guo-Yong , Robinson David W. , Chalupa Leo M.
Published: December 2017

Wang, Guo-Yong, David W. Robinson, and Leo M. Chalupa. Calcium-activated potassium conductances in retinal ganglion cells of the ferret. J. Neurophysiol. 79: 151–158, 1998. Patch-clamp recordings were made from isolated and intact retinal ganglion cells (RGCs) of the ferret to examine the calcium-activated potassium channels expressed by these neurons and to determine their functional role in the generation of spikes and spiking patterns. Single-channel recordings from isolated neurons revealed the presence of two calcium-sensitive potassium channels that had conductances of 118 and 22 pS. The properties of these two channels were shown to be similar to those ascribed to the large-conductance calcium-activated potassium channel (BKCa) and small-conductance calcium-activated potassium channel (SKCa) channels in other neurons. Whole cell recordings from isolated RGCs showed that apamin and charybdotoxin (CTX), specific blockers of the SKCa and BKCa channels, respectively, resulted in a shortening of the time to threshold and a reduction in the hyperpolarization after the spike. Addition of these blockers also resulted in a significant increase in spike frequency over a wide range of maintained depolarizations. Similar effects of apamin and CTX were observed during current-clamp recordings from intact alpha and beta ganglion cells, morphologically identified after Lucifer yellow filling. About 20% of these neurons did not exhibit a sensitivity to either blocker, suggesting the presence of functionally distinct subgroups of alpha and beta RGCs on the basis of their intrinsic membrane properties. The expression of these calcium-activated potassium channels in the majority of alpha and beta cells provides a means by which the activity of these output neurons could be modulated by retinal neurochemicals.
Direct Comparison of Heat-Evoked Activity of Nociceptive Neurons in the Dorsal Horn With the Hindpaw Withdrawal Reflex in the Rat
Authors: Morgan Michael M.
Published: December 2017

Morgan, Michael M. Direct comparison of heat-evoked activity of nociceptive neurons in the dorsal horn with the hindpaw withdrawal reflex in the rat. J. Neurophysiol. 79: 174–180, 1998. Although the sensory coding of nociceptive neurons in the dorsal horn has been studied extensively, surprisingly little is known about how these neurons contribute to nociceptive reflexes. The objective of the present study was to examine the characteristics of dorsal horn neurons capable of initiating hindpaw withdrawal. To this end, neural and reflex activity were measured simultaneously in response to noxious radiant heat applied to the hindpaw in lightly anesthetized rats. Subsets of both multireceptive (MR; 52/95) and nociceptive-specific (NS; 19/46) neurons showed a consistent burst of activity that preceded the reflex. However, when compared with NS neurons, MR neurons as a group were: more likely to be active before the reflex (55 vs. 41%); more active before the reflex (31 vs. 23 Hz); and active earlier (2.8 vs. 2.3 s before the reflex). Subsets of MR neurons were active before the reflex regardless of receptive field size or location in the dorsal horn. In contrast, NS neurons with small receptive fields or those located outside of superficial laminae were rarely active before the reflex and thus unlikely to be part of the reflex circuit. These results suggest that current classification schemes, in particular MR and NS categories, cannot be used as the sole criterion to predict involvement in nociceptive reflexes. However, simultaneous measurement of neural and reflex activity provides an opportunity to determine the characteristics of nociceptive neurons involved in withdrawal reflexes.
Modulation of Sustained and Transient Lateral Inhibitory Mechanisms in the Mudpuppy Retina During Light Adaptation
Authors: Cook Paul B. , McReynolds John S.
Published: December 2017

Cook, Paul B. and John S. McReynolds. Modulation of sustained and transient lateral inhibitory mechanisms in the mudpuppy retina during light adaptation. J. Neurophysiol. 79: 197–204, 1998. Two functionally and anatomically distinct types of lateral inhibition contribute to the receptive field organization of ganglion cells in the vertebrate retina: sustained lateral inhibition (SLI), which is present during steady illumination and transient lateral inhibition (TLI), evoked by changes in illumination. We studied adaptive changes in these two lateral inhibitory mechanisms in the mudpuppy retina by measuring the responses of on-off ganglion cells to spots of light in the receptive field center, in the absence and presence of a concentric broken annulus (windmill) pattern, which was either stationary or rotating. SLI was measured as the percent suppression of the centered spot response by the stationary windmill and TLI was measured as the additional suppression produced when the windmill was rotating. In dark-adapted retinas SLI was elicited by windmills of 600 or 1,200 μm ID, but TLI could not be elicited by windmills of any size, over a wide range of windmill intensities and rotation rates. Exposure of dark-adapted retinas to diffuse adapting light caused an immediate decrease in the response to the spot alone, followed by slowly developing changes in both SLI and TLI: SLI produced by 1,200 μm ID windmills became weaker, whereas SLI produced by 600 μm ID windmills became stronger. After several minutes strong TLI could be elicited by both 600 and 1,200 μm ID windmills. The changes in SLI and TLI were usually complete within 5 and 15 min, respectively, and recovered to dark-adapted levels slightly more slowly after the adapting light was turned off. However the changes in sensitivity of the spot response were complete within one minute after onset and termination of the adapting light. The adaptive changes in SLI and TLI did not depend on the presence of the adapting light; after a brief (1 min) exposure to the adapting light, the changes in SLI and TLI slowly developed and then decayed back to the dark-adapted level. The effects of the adapting light on SLI were mimicked by dopamine and blocked by D1 dopamine receptor antagonists. However dopamine did not enable TLI in dark-adapted retinas and dopamine antagonists did not prevent enablement of TLI when dark-adapted retinas were exposed to light or disable TLI when applied to light-adapted retinas. The results suggest that light-adaptive changes in SLI are mediated by dopamine and are consistent with a reduction in electrical coupling between neurons that conduct the SLI signal laterally in the retina. In contrast, TLI appears to be switched off or suppressed in the dark-adapted retina and enabled in light-adapted retinas, by a relatively slow modulatory mechanism that does not involve dopamine.
Gustatory and Multimodal Neuronal Responses in the Amygdala During Licking and Discrimination of Sensory Stimuli in Awake Rats
Authors: Nishijo Hisao , Uwano Teruko , Tamura Ryoi , Ono Taketoshi
Published: December 2017

Nishijo, Hisao, Teruko Uwano, Ryoi Tamura, and Taketoshi Ono. Gustatory and multimodal neuronal responses in the amygdala during licking and discrimination of sensory stimuli in awake rats. J. Neurophysiol. 79: 21–36, 1998. The amygdala (AM) receives information from various sensory modalities via the neocortex and directly from the thalamus and brain stem and plays an important role in ingestive behaviors. In the present study, neuronal activity was recorded in the AM and amygdalostriatal transition area of rats during discrimination of conditioned sensory stimuli and ingestion of sapid solutions. Of the 420 responsive neurons, 227 responded exclusively to one sensory modality, 120 responded to two or more modalities, and the remaining 73 could not be classified. Among the responsive neurons, 108 responded to oral-sensory stimulation (oral-sensory neurons). In detailed analyses of 84 of these oral-sensory neurons, 24 were classified as taste responsive and were located mainly in the central nucleus of the AM. The other 60 oral-sensory neurons were classified as nontaste oral-sensory neurons and were distributed widely throughout the AM. Both the taste and nontaste oral-sensory neurons also responded to other sensory stimuli. Of the 24 taste neurons, 21 were tested at least with four standard taste solutions. On the basis of the magnitudes of their responses to these sapid stimuli, the taste neurons were classified as follows: seven sucrose-best, four NaCl-best, three citric acid-best, and six quinine HCl-best. The remaining cell responded significantly only to lysine HCl and monosodium glutamate. Multivariate analyses of these 21 taste neurons suggested that, in the AM, taste quality was processed based on palatability. Taken with previous lesion studies, the present results suggest that the AM plays a role in the evaluation of taste palatability and in the association of taste stimuli with other sensory stimuli.
Pharmacological Properties of T-Type Ca2+ Current in Adult Rat Sensory Neurons: Effects of Anticonvulsant and Anesthetic Agents
Authors: Todorovic Slobodan M. , Lingle Christopher J.
Published: December 2017

Todorovic, Slobodan M. and Christopher J. Lingle. Pharmacological properties of T-type Ca2+ current in adult rat sensory neurons: effects of anticonvulsant and anesthetic agents. J. Neurophysiol. 79: 240–252, 1998. We have used the whole cell patch-clamp method to study pharmacological properties of low-voltage–activated (LVA) Ca2+ current in freshly dissociated neurons from dorsal root ganglia of adult rats. Inward barium current [in the presence of internal fluoride to reduce L-type high-voltage–activated (HVA) and external 1 μM ω-conotoxin GVIA to blockN-type HVA current] was evoked from negative holding potentials of −90 mV to test potentials of −25 mV and showed complete inactivation during 200-ms test pulses. Amiloride blocked ∼90% of current with half-maximal block (EC50) of 75 μM and a Hill coefficient ( n) of 0.99. LVA current was blocked completely by inorganic Ca2+ channel blockers: lanthanum (EC50 = 0.53 μM) > zinc (EC50 = 11.3 μM) > cadmium (EC50 = 20 μM)> nickel (EC50 = 51 μM). The antiepileptics, ethosuximide (EC50 = 23.7 mM, n = 1.4), phenytoin (EC50 = 7.3 μM, n = 1.3), α-methyl-α-phenylsuccinimide (EC50 = 170 μM, n = 2.1), and valproic acid (EC50 = 330 μM, n = 1.9) maximally blocked ∼100, 60, 26, and 17% of T current, respectively. Another antiepileptic, carbamazepine (≤100 μM), and convulsants such as pentylenetetrazole (1 mM) and tert-butyl-bicyclo [2.2.2] phosphorothionate (50 μM) had no effect on T current. Barbiturates completely blocked T current: thiopental (EC50 = 153 μM, n =1.2) > pentobarbital (EC50 = 334 μM, n = 1.2) > methohexital (EC50 = 502 μM, n = 1.3) > phenobarbital (EC50 = 1.7 mM, n = 1.2). Blockade by thiopental and pentobarbital did not show voltage or use dependence. General anesthetics blocked T current completely and reversibly: propofol (EC50 = 12.9 μM, n = 1.3) > octanol(EC50 = 122 μM, n = 1.2) > etomidate (EC50 = 205 μM, n =1.3) > isoflurane (EC50 = 303 μM, n = 2.3) > halothane (EC50 = 655 μM, n = 2.0) > ketamine (EC50 = 2.5 mM, n = 1.1). Mibefradil, a novel Ca2+ channel blocker, blocked dorsal root ganglion T current in a voltage- and use-dependent fashion with an EC50 of ∼3 μM( n = 1.3). When compared with results on other T currents, these data indicate that significant differences exist among different T currents in terms of pharmacological sensitivities. Furthermore, differences in pharmacological sensitivity of T currents among peripheral neurons, CNS, and neuroendocrine cells may contribute to the spectrum of effects of particular analgesic, anticonvulsant, and anesthetic drugs.
Interdependence of Spatial Properties and Projection Patterns of Medial Vestibulospinal Tract Neurons in the Cat
Authors: Perlmutter S. I. , Iwamoto Y. , Baker J. F. , Peterson B. W.
Published: December 2017

Perlmutter, S. I., Y. Iwamoto, J. F. Baker, and B. W. Peterson. Interdependence of spatial properties and projection patterns of medial vestibulospinal tract neurons in the cat. J. Neurophysiol. 79: 270–284, 1998. Activity of vestibular nucleus neurons with axons in the ipsi- or contralateral medial vestibulospinal tract was studied in decerebrate cats during sinusoidal, whole-body rotations in many planes in three-dimensional space. Antidromic activation of axon collaterals distinguished between neurons projecting only to neck segments from those with collaterals to C6and/or oculomotor nucleus. Secondary neurons were identified by monosynaptic activation after labyrinth stimulation. A three-dimensional maximum activation direction vector (MAD) summarized the spatial properties of 151 of 169 neurons. The majority of secondary neurons (71%) terminated above the C6segment. Of these, 43% had ascending collaterals to the oculomotor nucleus (VOC neurons), and 57% did not (VC neurons). The majority of VOC and VC neurons projected contralaterally and ipsilaterally, respectively. Most C6-projecting neurons could not be activated from oculomotor nucleus (V-C6neurons) and projected primarily ipsilaterally. All VO-C6neurons projected contralaterally. The distributions of MADs for secondary neurons with different projection patterns were different. Most VOC (84%) and contralaterally projecting VC (91%) neurons had MADs close to the activation vector of a semicircular canal pair, compared with 54% of ipsilaterally projecting VC (i-VC) and 39% of V-C6neurons. Many i-VC (44%) and V-C6(48%) neurons had responses suggesting convergent input from horizontal and vertical canal pairs. Horizontal and vertical gains were comparable for some, making it difficult to assign a primary canal input. MADs consistent with vertical-vertical canal pair convergence were less common. Type II yaw or type II roll responses were seen for 22% of the i-VC neurons, 68% of the V-C6neurons, and no VOC cells. VO-C6neurons had spatial properties between those of VOC and V-C6neurons. These results suggest that secondary VOC neurons convey semicircular canal pair signals to both ocular and neck motor centers, perhaps linking eye and head movements. Secondary VC and V-C6neurons carry more processed signals, possibly to drive neck and forelimb reflexes more selectively. Two groups of secondary i-VC neurons exhibited vertical-horizontal canal convergence similar to that present on neck muscles. The vertical-vertical canal convergence present on many neck muscles, however, was not present on medial vestibulospinal neurons. Spatial transformations achieved by the vestibulocollic reflex may occur in part on secondary neurons but further combination of canal signals must take place to generate compensatory muscle activity.