bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective inhibition of glucose-sensitive neurons in rat lateral hypothalamus by noxious stimuli and morphine
Authors: Sikdar S. K. , Oomura Y.
Published: December 2017

On the basis of their responsiveness to electrophoretically applied glucose, neurons in the lateral hypothalamic area (LHA) have been characterized as either glucose sensitive or glucose nonsensitive. Glucose-sensitive neurons are important in feeding control (4, 36-38, 44, 54). The aim of this study was to increase understanding of the neurophysiological mechanisms involved in the disturbance of feeding by pain. Radiant heating of the scrotum, strong tail pinch, and immersion of the tail in hot water were used as noxious stimuli. In order to correlate the responses of LHA neurons to noxious inputs with possible local release of endogenous opiates, effects of electrophoretically applied morphine and naloxone were also tested. The effects of glucose, morphine, and noxious stimulation were studied in a total of 165 neurons recorded from 75 adult male urethane-chloralose-anesthetized rats. Of 52 neurons determined to be glucose sensitive, 36 (69%) were inhibited by both noxious stimulation and morphine. A majority of the glucose-nonsensitive neurons did not respond to either morphine or noxious stimulation (87/113, 74%). The relation of glucose sensitivity to inhibition by pain and/or morphine was statistically significant (Fisher's exact probability test, P less than 0.01). Naloxone attenuated the inhibitory effects of both pain and morphine, thus suggesting mediation of both by the same neuronal mechanism. From this evidence we conclude that LHA glucose-sensitive neurons are involved in the suppression of feeding by noxious stimulation.
Calcium spike and calcium-dependent potassium conductance in mechanosensory neurons of the lamprey
Authors: Leonard J. P. , Wickelgren W. O.
Published: December 2017

Action potentials (APs) of long duration (up to 1 s) followed by prolonged (0.5-5 s) hyperpolarizing afterpotentials (HAP) were recorded in lamprey primary mechanosensory neurons (dorsal cells) in isolated spinal cords exposed to either or both of the potassium channel blockers, tetrathylammonium (TEA) and 3,4-diaminopyridine (DAP). The membrane events underlying the prolonged AP and HAP were investigated in current clamp studies and were shown to be a Ca spike- and a Ca-dependent K conductance, respectively. The prolonged AP was accompanied by an increased membrane conductance and, unlike the normal Na AP in these cells, was not blocked by tetrodotoxin (TTX) or by replacement of external Na with choline or TEA. Reduction of [Ca]o from 10 to 0 mM reduced the amplitude and duration of the prolonged TTX-resistant AP but did not eliminate it within the 15-min washout period, probably because of Ca buffering in the spinal cord. The overshoot of the prolonged AP varied in amplitude as a linear function of the log of the external Ca concentration (2.5-10 mM) with a slope of 31.5 mV for a 10-fold change in Ca concentration, a value close to the 28 mV expected from the Nernst relation. Co (2 mM) and Cd (1 mM) blocked the prolonged APs. Ba and Sr substituted for Ca. The APs in Ba were extremely long lasting (up to 40 s). The HAPs following Ca spikes were 0.5-5 s in duration (peak to half amplitude) and were accompanied by an increased membrane conductance. The HAP varied in amplitude with the extracellular K concentration, reversed in sign at the presumed K equilibrium potential (-90 mV), and was insensitive to injected Cl. We conclude that HAP is a result of increased K conductance. The increase in K conductance during the HAP appeared to be dependent on Ca influx, because the amplitude and duration of the HAP varied with the extracellular Ca concentration and increased in duration during repetitive Ca spike activation, presumably as a result of accumulation of Ca intracellularly. Further, the HAP was absent following even very long lasting spikes in Ba, an ion that in other cells does not activate the Ca-dependent K conductance. Small regenerative depolarizations sometimes followed Ca spikes in dorsal cell somata. These are believed to reflect Ca spikes in discrete axonal regions at various electrotonic distances from the soma.
Segmental differences in pathways between crayfish giant axons and fast flexor motoneurons
Authors: Miller L. A. , Hagiwara G. , Wine J. J.
Published: December 2017

We have used electrophysiological techniques to document segmental differences in the pathways between the giant, escape command axons, lateral giants (LG) and medial giants (MG), and the nongiant, fast flexor (FF) motoneurons. We found no difference in the input from LG and MG axons to FF motoneurons in the posterior (4th and 5th) ganglia. Since flexor motor output in these segments would be inconsistent with the LG-evoked behavior pattern, this finding was puzzling. Electromyographic (EMG) recordings during escape responses by intact unrestrained animals confirm that the FF muscles innervated by the posterior ganglia are not excited during LG-mediated tailflips, but are excited during MG-mediated tailflips. In the 2nd and 3rd ganglia, the command axons fire the FF motoneurons with high probability, in part via electrical excitatory postsynaptic potentials (EPSPs) from premotor neurons, the segmental giants (SG). In the 4th and 5th ganglia, the equivalent pathway is much less effective. Single, directly elicited impulses in SGs in ganglia 2 and 3 fire their respective FF motoneurons with high probability, while those in ganglia 4 and 5 rarely fire FF motoneurons. The command axons fire the SGs reliably in all segments. The amplitude of the SG-evoked EPSP in FF motoneurons is significantly smaller in posterior vs. anterior ganglia. For technical reasons, we are unable to present conclusive evidence on ganglionic variations in FF-motoneuron thresholds. The FF motoneurons receive additional excitatory input from intersegmental interneurons recruited by the command neurons. Motoneurons in ganglia 4 and 5 are excited by large interneurons that do not synapse on motoneurons in ganglia 2 and 3, but this additional input is not sufficient to compensate for the weaker effect of SG input. Unlike the all-or-none segmental differences demonstrated previously for the LG-to-motor giant pathway (24), the SG-to-FF pathway changes gradually, retains significant though subthreshold strength in posterior ganglia, and is common to both LGs and MGs. These features provide opportunities for variation in the spatial patterning of flexion and in the resulting escape trajectories.
Signal transmission in the catfish retina. III. Transmission to type-C cell
Authors: Sakuranaga M. , Naka K.
Published: December 2017

Current injected into horizontal-cell somas and axons produced transient (on-off) depolarizations from type-C cells (commonly known as transient amacrine cells) similar to those produced by light. Both the light- and current-induced responses had very small linear components and nonlinear components as represented by the second-order kernels, which reproduced the cell's response with a reasonable degree of accuracy. The second-order kernels were well defined and stereotyped. The quadratic nature of the nonlinear component is reflected in the frequency doubling response as well as the very steep input-output relationship of the cell. Type-C cell's responses evoked by light and current differed in a subtle but distinct fashion, and this difference appeared in the signature of the second-order kernels. The light-produced kernels had two diagonal positive peaks and off-diagonal valleys ("four-eye" structure), whereas the current-produced kernels had a single on-diagonal positive peak with off-diagonal negative valleys ("three-eye" structure). The difference in the kernel configuration was reflected in the cell's step-evoked response. Some type-C cells produced faster responses whereas others produced slower responses, whether evoked by light or by current. Our past and present results show that type-C cells produce a very nonlinear response that is not necessarily complex.
Mechanisms of pattern generation underlying swimming in Tritonia. IV. Gating of central pattern generator
Authors: Getting P. A. , Dekin M. S.
Published: December 2017

Swimming behavior in the marine mollusc Tritonia diomedea is episodic, consisting of a series of alternating dorsal and ventral flexions initiated by a brief sensory stimulus. The swim motor pattern is generated by a network formed of four groups of premotor interneurons: cerebral cell 2 (C2), dorsal swim interneurons (DSIs), and two types of ventral swim interneurons (VSI-A and VSI-B). The initiation and maintenance of swimming depends on the establishment of a long-lasting ramp depolarization in both the premotor, pattern-generating interneurons, and the motor neurons (i.e., flexion neurons). Voltage clamp was used to measure the membrane current responsible for the ramp depolarization. In all cell classes the current had two components: a tonic inward current, which decayed as the swim progressed, and phasic inward current waves, which provided the synaptic drive during each swim burst. The ramp current in the flexion neurons and in C2 was generated largely by activity within the interneuronal pattern-generating network (PGN). The ramp current could be mimicked by driving activity in the pattern-generating interneurons. In VSI-B, the tonic component of the ramp current was independent of activity within the PGN and appeared to be derived from the long-lasting effect of an extrinsic input. The phasic components of the ramp, however, were dependent on PGN activity. The phasic inward current waves were blocked when pattern generation was prevented. In addition, phasic inward currents similar to those occurring during swimming could be produced by driving the C2. The tonic component of the ramp current in a DSI was dependent both on extrinsic inputs and PGN activity. Extrinsic inputs appeared to control the first 10-15 s of the tonic current. At longer times, activity within the DSI population itself maintained the ramp current. When one DSI was driven in a quiescent preparation, all other DSIs were inhibited, yet the DSIs are known to be coupled by monosynaptic, reciprocal excitatory synapses. This effect could be explained by the action of an unidentified inhibitory interneuron (I-neuron), which was excited by DSIs and in turn inhibited all other DSIs. The DSIs were therefore coupled reciprocally by both monosynaptic excitation and polysynaptic inhibition. Activity in C2 switched the DSI-DSI interaction from inhibition to excitation by inhibiting the I-neuron.(ABSTRACT TRUNCATED AT 400 WORDS)
Histaminergic synaptic transmission in the cerebral ganglion of Aplysia
Authors: McCaman R. E. , Weinreich D.
Published: December 2017

Standard intracellular stimulating and recording techniques including voltage-clamp were used to analyze the synaptic responses mediated by two identifiable histamine-containing neurons (HCNs), designated C2 neurons, located in bilaterally symmetric clusters of the isolated cerebral ganglion of Aplysia california. Activation of each C2 induced unitary chemically mediated synaptic potentials in over 15 identified ipsilateral follower neurons. Several additional followers were connected to the HCNs by nonrectifying electrical synapses. Most of the follower neurons examined received only chemical synapses from the C2s. Some of the followers were reciprocally connected with each other through nonrectifying electrical synapses. A single C2 action potential can evoke six distinctive types of chemically mediated postsynaptic potentials (PSPs) in different follower neurons. Most of the PSPs have been shown to be multicomponent, i.e., they are comprised of various combinations of individual fast (less than or equal to 150 ms), slow (1-2 s), and very slow (greater than or equal to 4 s) depolarizing and hyperpolarizing components. The combination of these components produces PSPs of varying complexity, from simple monophasic responses such as the frequently observed slow excitatory PSPs and slow inhibitory PSPs to responses consisting of two to three components such as fast excitatory, slow inhibitory PSPs or fast inhibitory, slow excitatory PSPs. All of the multicomponent PSPs appear to be mediated through monosynaptic connections from the C2, as determined by various electrophysiological criteria. The slow and very slow synaptic components of the multicomponent PSPs were markedly potentiated in amplitude and duration after repetitive C2 activation. This property of the slow components permits the slower PSPs to exert a major influence on the excitability and integrative properties of the follower neurons.
Flight-initiating interneurons in the locust
Authors: Pearson K. G. , Reye D. N. , Parsons D. W. , Bicker G.
Published: December 2017

We have used intracellular recording and staining techniques to investigate the cellular mechanisms for the initiation and maintenance of flight in the locust, Locusta migratoria. In particular, we examined the properties of a small group of interneurons in the mesothoracic ganglion. We refer to these interneurons as 404 neurons. Their structure has been described, in a closely related species, by Watson and Burrows (21). Using a preparation in which intracellular recordings could be made from the main neurite of a 404 neuron during the generation of flight activity, we observed that the 404 neurons discharged tonically throughout flight episodes elicited by a constant wind stimulus on the head and by a sudden dimming of the lights. Their discharge rate was linearly related to the frequency of the flight activity. Depolarization of individual 404 neurons often initiated flight activity in quiescent preparations, and the application of hyperpolarizing currents during a flight episode either slowed or stopped flight activity. Hyperpolarizing currents also prevented the initiation of flight activity in some preparations. Individual 404 neurons were not always necessary for the generation of flight activity, since flight activity sometimes persisted when all spiking in a 404 neuron was prevented by the application of a hyperpolarizing current. We conclude that the 404 neurons function to initiate and maintain flight activity in response to wind stimulation of the head, but we have not yet established that they are the only thoracic neurons with this function. The 404 neurons discharged with a high-frequency burst at the time of triggering of a kick. Since the motor program for a jump is similar to that for a kick, the 404 neurons may also be involved in linking the initiation of flight activity to the jump. None of our data indicate that the 404 neurons receive input from the central rhythm generator. Thus the neuronal circuitry for flight appears to be hierarchically organized with at least one distinct neuronal system providing a tonic drive to initiate and maintain activity in the system that patterns activity in flight motoneurons.
Axonal projections of single bulbospinal inspiratory neurons revealed by spike-triggered averaging and antidromic activation
Authors: Dick T. E. , Berger A. J.
Published: December 2017

Activity was recorded extracellularly from 26 inspiratory bulbospinal neurons in anesthetized, paralyzed, artificially ventilated cats. All but one were located in the ventral respiratory group. A neuron was classified as either I alpha or I beta by comparing its firing pattern during inspiratory cycles with lung inflation to its pattern when lung inflation was withheld during the central inspiratory phase (2, 14, 15). In this study, the projection and conduction velocity of these axons were determined using two methods: antidromic activation (AA) of the bulbospinal neurons and spike-triggered averaging (STA) of the extracellular field potentials. These methods have been compared directly because the same electrode was used both for stimulating the axon of the bulbospinal neuron and recording its axonal potential in the same location. Axonal projections from these neurons were mapped in the contralateral spinal cord with a mobile electrode by determining where the lowest stimulus threshold occurs for AA and greatest axonal potential can be recorded with STA. The locations of these axons were in the ventral and lateral funiculi. Each method determined a similar location for an axon. Positions of 10 axons were determined at both the third (C3) and fourth (C4) cervical segments. Single axons maintained their positions in either descending tract from rostral C3 to mid-C4. In five of six cases where two “neighboring” medullary units were characterized, the axons of each pair projected together within 350 micron of each other in the cervical spinal cord. Estimates of mean axonal conduction velocity (CV) from antidromic activation from a single stimulus site, “single-point AA,” were as much as 42% less than corresponding estimates from STA extracellular field potentials at that point (P less than 0.001). Such single-point estimates were less than determinations that were calculated from the difference in conduction time and the difference in conduction distance from two points in the spinal cord. These two-point determinations averaged 55.4 +/- 13.1 m/s (using AA) and 53.3 +/- 13.1 (using STA) for 10 neurons. These values were not significantly (P greater than 0.2) different from each other and are greater than most earlier reports, which used the single-point AA method. Either method, AA or STA, can be used to determine axonal position and CV. The advantages and disadvantages of each method are discussed.(ABSTRACT TRUNCATED AT 400 WORDS)
Properties of visceral primary afferent neurons in the nodose ganglion of the rabbit
Authors: Stansfeld C. E. , Wallis D. I.
Published: December 2017

The active and passive membrane properties of rabbit nodose ganglion cells and their responsiveness to depolarizing agents have been examined in vitro. Neurons with an axonal conduction velocity of less than 3 m/s were classified as C-cells and the remainder as A-cells. Mean axonal conduction velocities of A- and C-cells were 16.4 m/s and 0.99 m/s, respectively. A-cells had action potentials of brief duration (1.16 ms), high rate of rise (385 V/s), an overshoot of 23 mV, and relatively high spike following frequency (SFF). C-cells typically had action potentials with a "humped" configuration (duration 2.51 ms), lower rate of rise (255 V/s), an overshoot of 28.6 mV, an after potential of longer duration than A-cells, and relatively low SFF. Eight of 15 A-cells whose axons conducted at less than 10 m/s had action potentials of longer duration with a humped configuration; these were termed Ah-cells. They formed about 10% of cells whose axons conducted above 2.5 m/s. The soma action potential of A-cells was blocked by tetrodotoxin (TTX), but that of 6/11 C-cells was unaffected by TTX. Typically, A-cells showed strong delayed (outward) rectification on passage of depolarizing current through the soma membrane and time-dependent (inward) rectification on inward current passage. Input resistance was thus highly sensitive to membrane potential close to rest. In C-cells, delayed rectification was not marked, and slight time-dependent rectification occurred in only 3 of 25 cells; I/V curves were normally linear over the range: resting potential to 40 mV more negative. Data on Ah-cells were incomplete, but in our sample of eight cells time-dependent rectification was absent or mild. C-cells had a higher input resistance and a higher neuronal capacitance than A-cells. In a proportion of A-cells, RN was low at resting potential (5 M omega) but increased as the membrane was hyperpolarized by a few millivolts. A-cells were depolarized by GABA but were normally unaffected by 5-HT or DMPP. C-cells were depolarized by GABA in a similar manner to A-cells but also responded strongly to 5-HT; 53/66 gave a depolarizing response, and 3/66, a hyperpolarizing response. Of C-cells, 75% gave a depolarizing response to DMPP.(ABSTRACT TRUNCATED AT 400 WORDS)
Dynamic control of the perioral system during speech: kinematic analyses of autogenic and nonautogenic sensorimotor processes
Authors: Gracco V. L. , Abbs J. H.
Published: December 2017

Afferent contributions to the motor control of speech were evaluated by applying unanticipated loads to the lower lip during the combined upper lip-lower lip gesture associated with the oral closing movements for a "b" sound. Loads were introduced randomly in approximately 15% of the trials to minimize subject anticipation or adaptation. A total of 490 load trials (in five naive subjects) were distributed within a restricted interval (100 ms) centered on the initiation of agonist muscle contraction associated with the lip-closing movements. Kinematic adjustments of the upper and lower lips to these perturbations were examined in detail. In all subjects, load-induced changes in upper and lower lip displacement, movement time, and closing velocity were statistically significant and observed the first time a perturbation was introduced. Load timing variations within the target interval resulted in systematic changes in the site of the compensatory adjustments (upper versus lower lip) and in the magnitude of the kinematic responses. These kinematic changes appeared to reflect the dynamic nature of underlying control processes and clearly contrasted the different response characteristics of autogenic (lower lip) and nonautogenic (upper lip) compensatory actions. Although both upper and lower lip adjustments contributed to perturbation compensations, autogenic responses were found to predominate when loads occurred 20-55 ms before muscle activation. For these early loads, autogenic responses provided approximately 75% of the total compensation. For later loads, when the evolving speech motor action was more time constrained, nonautogenic (open-loop) compensations predominated, providing approximately 65% of the total compensation. The variations in upper and lower lip compensatory response magnitude did not parallel the time course of facial muscle activation. Lower lip kinematic adjustments were reduced 10-15 ms prior to the onset of agonist muscle activation, whereas upper lip adjustments increased in magnitude 10-20 ms after agonist onset. Apparently the dynamic modulation of these responses is controlled independently from facial motoneuron excitation, possibly involving sensorimotor processing via supranuclear centers. Overall the compensatory movement displacements were highly related to the magnitude of the perturbation displacement, especially for loads introduced prior to agonist muscle onset, reflecting a well-calibrated readjustment.(ABSTRACT TRUNCATED AT 400 WORDS)
Activity of respiratory neurons during NREM sleep
Authors: Orem J. , Osorio I. , Brooks E. , Dick T.
Published: December 2017

The purpose of this study was to analyze differences in the activity of medullary respiratory neurons in the unanesthetized, intact cat during wakefulness and non-rapid-eye-movement (NREM) sleep. We studied single respiratory neurons located within a 1-2 mm deep, 8-10 mm long zone that followed, and included in its dorsal aspect, the retrofacial and ambiguus nuclei. The analysis of variance was used to detect respiratory activity, and cycle-triggered histograms were plotted. The respiratory signal strength and consistency of the respiratory activity were quantified with the eta 2 statistic. We determined for each breath in wakefulness and NREM sleep the average discharge rate during the active phase of the cell, the number of action potentials during the active phase of the cell, and durations of both the cycle and inspiration. Differences in discharge rates and in the number of discharges between wakefulness and NREM sleep were tested with the t test. A bimodal distribution of eta 2 values for the population of neurons indicated there were two groups of respiratory cells: those with eta 2 values less than 0.3 and those with values greater than 0.3. The former we call weak respiratory cells; the latter, strong respiratory cells. Strong and weak cells were classified further as inspiratory or noninspiratory on the basis of the shape of their cycle-triggered histograms. Within the class of strong inspiratory cells, those with the highest eta 2 values 1) reached their peak discharge rate early, 2) discharged at high rates throughout inspiration, and 3) were inactive during expiration. The values of these variables diminished progressively in inspiratory cell groups with lower eta 2 values. Most cells were less active in NREM sleep than in wakefulness. Similar proportions of weak and strong cells and inspiratory and noninspiratory cells were affected by sleep. The reduction in sleep of the activity of strong inspiratory cells was consistent with a general relationship between this activity and the duration of inspiration. Lower discharge rates were associated with longer breaths; higher rates with shorter breaths. This relationship existed within both NREM sleep and wakefulness, and the plot of the relationship across these states formed a continuous function. The reduction in discharge rate in sleep was greater for weak than for strong inspiratory cells: the correlation coefficient between percent change in rate and eta 2 values was -0.636 for inspiratory cells, but it was not significant (-0.265) for noninspiratory cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Ionic currents of cultured horizontal cells isolated from white perch retina
Authors: Lasater E. M.
Published: December 2017

Horizontal cells from the retinas of white perch were isolated and maintained in cell culture for 3 days to 3 wk. Four morphologically distinct types of horizontal cells could be identified in culture and were labeled types H1, H2, H3, and H4. Whole-cell patch-clamp techniques were used to study the ionic currents present in the four cell types. In all cells, depolarizing commands above threshold elicited a fast-inward current followed by an outward current. The fast-inward current was abolished by tetrodotoxin (TTX) or 0 Na+ Ringer's, indicating the current was carried by Na+. In H1, H2, and H3 cells, the outward current, carried by K+, consisted of two components: a transient current (IA), blockable with 4-aminopyridine (4-AP), tetraethylammonium (TEA), or intracellular cesium and a sustained current that could be blocked with TEA. The H4 cell had only the sustained current. An inward rectifying K+ current (anomalous rectifier) was observed in the four cell types. The current was sensitive to the extracellular K+ concentration. Its activation showed two components: an instantaneous component and a slower component. The slow component becomes faster with greater hyperpolarizations. The four cell types possessed a small, sustained Ca2+ current that, under normal conditions, was masked by the inward Na+ current and outward K+ currents.
Pattern of convergence of the receptors of the barnacle's three ocelli onto second-order cells
Authors: Oland L. A. , Stuart A. E.
Published: December 2017

The giant barnacle, Balanus nubilus, has three simple eyes, two lateral and one median. We have studied the convergence of the receptors of these ocelli by recording from the second-order cell (I-cell) and from the receptors' terminals. The I-cell's responses to illumination of the median and lateral eyes are similar in shape, dynamic range, and reversal potential, but the response to lateral input has a longer latency, a slower rise time, and a smaller amplitude. These differences primarily reflect the different voltage changes in the terminals of the decrementally conducting median and lateral receptors. Simultaneous recordings from the terminals of median and lateral receptors showed that the responses to light recorded in lateral terminals had a longer latency, a slower rise time, and smaller amplitude than signals in median terminals. The differences in the I-cell's responses to median and lateral input were essentially eliminated by stimulating the median and lateral ocellar nerves with extracellular suction electrodes positioned at equal distances from the receptors' terminals. The similarity of the I-cell's responses to median and lateral input suggests that lateral photoreceptors, like median receptors, contact the I-cell directly. No evidence was found for interaction between median and lateral receptors. Simultaneous fills of median and lateral receptors with cobalt showed minimal overlap between their terminal arbors. No voltage change was detected in the second receptor when the voltage in the first was changed with current pulses or when action potentials were elicited in the presence of tetraethylammonium ions. The absence of a detectable response in the terminals of one eye's receptors when the receptors of the other eye were stimulated with current or light suggests that there is no feedback from the I-cell to the receptors. Simultaneous illumination of the median and lateral eyes produced responses in the I-cell expected from two independent inputs. The first synaptic stage of the visual pathway in the barnacle is thus unusually simple, consisting of a small number of electrically isolated photoreceptors converging upon the same pair of second-order cells with no feedback interaction.
Altered excitability of goldfish Mauthner cell following axotomy. II. Localization and ionic basis
Authors: Titmus M. J. , Faber D. S.
Published: December 2017

The ionic basis and spatial localizations of spike generation were examined in normal and axotomized goldfish Mauthner (M-) cells using intra- and extracellular recordings and pharmacological manipulation of ionic conductances, including localized iontophoretic drug applications. Tetrodotoxin (TTX) abolished both the initial segment (IS) spike in normal cells and the larger, two-component action potential in axotomized cells, whereas calcium (Ca2+) blockers did not. Thus, sodium (Na+) appears to be the major inward current carrier in both cases. A shoulder or plateau following the fast-rising Na+-dependent action potential was unmasked in both normal and axotomized M-cells by intracellular injections of tetraethylammonium (TEA), either alone or in conjunction with 4-aminopyridine (4-AP) or cesium (Cs+). This plateau potential was abolished by superfusing with saline containing the Ca2 antagonists, Co2+, Mn2+, or Cd2+. However, barium (Ba2+), which normally substitutes for Ca2+ and also blocks K+ conductances, did not produce a plateau spike, and no action potentials could be evoked in the presence of TTX. Simultaneous extra- and intracellular recordings from the soma and lateral dendrite revealed that both the full-sized axotomized spike and its individual labile components were always maximal at the soma. These data support the earlier suggestion that the axotomy-induced electrogenicity is primarily localized to that region. Iontophoretic application of TTX inside the axon cap, a distinctive neuropil surrounding the initial segment and the axon hillock and circumscribed by a glial border, and at various positions along the lateral dendrite confirmed the Na+-dependency of the action potentials recorded in normal and axotomized cells and further demonstrated that the soma generates the additional spike component in the latter. The results suggest that axotomy causes a persistent change in voltage-gated Na+ channel distribution in the M-cell, with Na+ channels appearing or becoming more numerous in the soma while becoming less concentrated in the initial segment-axon hillock. Possible related shifts in other voltage-dependent conductances are also discussed. Finally, these are the first detailed studies of the ionic basis of axotomy-induced electrogenicity in a vertebrate neuron, central or peripheral, and the similarity to the results obtained with invertebrate neurons suggests common mechanisms underlying the axon reaction.
Voltage-clamp analysis of currents produced by glutamate and some glutamate analogues on horizontal cells isolated from the catfish retina
Authors: Hals G. , Christensen B. N. , O'Dell T. , Christensen M. , Shingai R.
Published: December 2017

Horizontal cells isolated from the catfish retina were exposed to radiolabeled glutamate, glycine, gamma-aminobutyric acid (GABA), and sucrose to determine if the enzymatic dissociation procedure altered the high-affinity uptake mechanism for GABA and generally reduced membrane selectivity. As in the intact retina, isolated cells could transport GABA but not the other substances. The horizontal cells were voltage clamped using a single low-resistance patch-type electrode. The acidic amino acid L-glutamate, and its analogues kainate and quisqualate, were applied to the cell by pressure ejection from a nearby pipette. All three agonists produced inward currents that reversed near O mV. Quisqualate produced a current with a similar time course as glutamate, but the time course of the response to kainate was faster. The agonists N-methyl-D-aspartate and L-aspartate had little effect on the membrane conductance. The current-to-voltage (I-V) relationship for all three agonists was nonlinear when the membrane potential was hyperpolarized. The nonlinearity was, at least in part, a result of the decreased response to the three agonists. Removal of Mg did not alter this nonlinear relationship. When the inward potassium rectifier was blocked with 100 microM Ba, the response to glutamate was increased compared with the control experiment before block by barium; however, the I-V relationship was still highly nonlinear. Thus glutamate block of the inward potassium current cannot account entirely for the nonlinear I-V. The increase in membrane permeability to specific ions in the presence of an agonist was determined by ion substitution experiments and measuring the shift in the reversal potential. The three agonists appear to increase the membrane permeability to cations but not to anions. The amino acid antagonists cis-2,3-piperidine dicarboxylic acid (PDA) and D-glutamyl glycine (DGG) were bath applied to test their ability to block the depolarizing effects of glutamate. DGG had no measureable effect at 100 microM concentration, whereas PDA reversibly reduced the glutamate response at 1 mM concentration although block was incomplete. Isolated horizontal cells responded to bath-applied glutamate in concentrations of 10-500 microM. In concentrations of glutamate greater than 50 microM, when the membrane potential was held at the resting potential, the inward current reached a maximum followed by a decrease to a steady-state level. This apparent time-dependent desensitization at high agonist concentrations was at least partially removed when Mg was removed from the bathing solution.(ABSTRACT TRUNCATED AT 400 WORDS)
A reexamination of the gain of the vestibuloocular reflex
Authors: Viirre E. , Tweed D. , Milner K. , Vilis T.
Published: December 2017

The properties of the vestibuloocular reflex (VOR) when the axis of rotation is behind the eyes and fixation of a near target is required were studied in the monkey. The magnitude of VOR gain in each eye was found to be above 1.0 and near the ideal value for stabilizing a retinal image. Evidence that this large VOR gain was not visually mediated was provided by the observations that no reduction in gain and no phase lag were observed at high frequencies of head rotation (2 Hz), large gain was observed in the dark, and large gain was observed within 10-20 ms of the start of head rotation. The magnitude of VOR gain was found to increase with increasing radius of head rotation and also to increase with decreasing target distance. When the distances from the two eyes to the target were different the instantaneous velocities and VOR gains of the eyes were also different. The dependence on radius of rotation indicates that the VOR is mediated by a combination of otolith and canal inputs. A general model for otolith-canal interaction is proposed in which VOR gain is based on a computation of target location relative to the head. This model simplifies to the classical VOR reflex when a cyclopean eye is subjected only to angular displacement.
High-frequency oscillations in human electromyograms during voluntary contractions
Authors: Bruce E. N. , Ackerson L. M.
Published: December 2017

Spectral analysis was used to identify correlated sinusoidal frequency components in left and right side diaphragm electromyographic (EMG) recordings from human subjects during voluntary deep inspirations. In 31 of 33 subjects bilaterally correlated high-frequency oscillations were found in broad or narrow bands in the range of 60-84 and 16-40 Hz. To determine if such oscillations were associated also with bilaterally symmetric, phasic, voluntary activation of nonrespiratory muscles, we obtained EMG signals from left and right masseter muscles during clenching of the jaw; left and right sternomastoid muscles during lifting of the head against gravity; and left and right biceps muscles during lifting of a weighted bar. Weakly correlated frequency components, mainly at frequencies below 60 Hz, were found in the left and right masseter EMGs on at least one trial from 12 of 17 subjects. No bilaterally correlated frequency components were found during phasic contraction of biceps and sternomastoid muscles. Power spectra of biceps EMGs, however, sometimes exhibited peaks indicative of oscillations that were not bilaterally correlated. In nine subjects, correlated frequency components in the 60-84 Hz range were found in intercostal EMGs from the axillary region of the fifth interspace during voluntary deep inspirations but not during postural contractions. We conclude that high-frequency oscillations in the range of 60-84 Hz in diaphragm and intercostal EMGs are associated particularly with respiratory activation of respiratory muscles. These results support the hypothesis that high-frequency oscillations may be a manifestation of control of muscular contraction via a central pattern generator.
Local nonspiking interneurons involved in gating of the descending motor pathway in crayfish
Authors: Takahata M. , Hisada M.
Published: December 2017

Uropod motor neurons in the terminal abdominal ganglion of crayfish are continuously excited during the abdominal posture movement so that subthreshold excitatory postsynaptic potentials from the descending statocyst pathway can elicit spike activity in the motor neurons only while the abdominal posture system is in operation. Local nonspiking interneurons in the terminal ganglion were also found to show sustained membrane potential change during the fictive abdominal posture movement. Artificial membrane potential change of these interneurons by intracellular current injection in the same direction as that actually observed during the abdominal movement caused similar excitation of uropod motor neurons. Artificial cancellation of the membrane potential change of these interneurons during the abdominal movement also caused cancellation of the excitation of uropod motor neurons. We concluded that the continuous excitation of uropod motor neurons during the fictive abdominal movement was mediated, at least partly, by the local nonspiking interneurons. Fourteen (36%) out of 39 examined nonspiking interneurons were judged to be involved in the excitation of uropod motor neurons during the fictive abdominal movement. Another 25 interneurons (64%) were found not to be involved in the excitation of motor neurons, although most of them had a strong effect on the uropod motor neuron activity when their membrane potential was changed artificially. The interneurons that were involved in the excitation of motor neurons during the abdominal movement included both of the two major structural types of nonspiking interneurons in the terminal ganglion, i.e., those in the anterolateral portion and those in the posterolateral portion. No strict correlation was found between the structure of nonspiking interneurons and their function in the control of uropod motor neuron activity.
Quantitative analysis of synaptic potentiation during kindling of the perforant path
Authors: Sutula T. , Steward O.
Published: December 2017

Synaptic transmission was studied during the development of kindling in the pathway from entorhinal cortex (EC) to dentate gyrus (DG) of unrestrained unanesthetized rats using chronic neurophysiological techniques. Extracellular field potentials were recorded from the DG in response to activation of the perforant pathway with 0.1-ms constant current square-wave pulses. The evoked field potentials consisted of a population EPSP (a reflection of excitatory synaptic activation) and a population spike (a measure of synchronous postsynaptic discharge of granule cells). Synaptic efficacy was quantitated in this pathway by measurement of the population EPSP slope and population spike amplitude across a range of stimulus intensities from threshold to maximal evoked response. Input-output relationships for population EPSP and population spike were determined at regular intervals during the course of kindling, corresponding to the stages of evoked behavioral seizures. Increases in the population EPSP and population spike were observed after a single kindling stimulus that evoked afterdischarge (AD) when behavioral seizures were minimal. Evaluation of the input-output relationships for the group of kindled animals at the various stages of evoked behavioral seizure activity revealed that increases in the population EPSP continued to slowly evolve with repeated stimulations but that increases in the population spike were maximal after one or at most a few stimulations that evoked AD. The increases in both population EPSP and population spike persisted for the duration of the recording, i.e., through induction of generalized motor convulsions. To evaluate the translation of synaptic activation into cell discharge during kindling, we made use of the population spike/population EPSP ratio across a range of stimulus intensities. The spike/EPSP ratios revealed a dissociation of the population spike and population EPSP early in the course of kindling during class 1 seizures. Specifically, after induction of an AD, an extracellular population EPSP of a given size evoked a larger population spike than an EPSP of comparable size before the induction of an AD by kindling stimulation. The development of generalized motor convulsions (class 5 seizures) was associated with a reduction in the spike/EPSP ratio. The mechanism of this reduction in spike/EPSP ratio is uncertain, but since synaptic activation (as reflected by population EPSP) did not decline during class 5 seizures, the reduction in the spike/EPSP ratio could be consistent with increased inhibition after generalized motor convulsions, or could reflect a decrease in granule cell excitability.(ABSTRACT TRUNCATED AT 400 WORDS)
Involvement of the dorsolateral funiculus in the descending spinal projections responsible for diffuse noxious inhibitory controls in the rat
Authors: Villanueva L. , Chitour D. , Le Bars D.
Published: December 2017

Recordings were made from convergent neurons in the lumbar dorsal horn of the spinal cord of the rat. These neurons were activated by both innocuous and noxious mechanical stimuli applied to their excitatory receptive fields located on the extremity of the hindpaw. Transcutaneous application of suprathreshold 2-ms square-wave electrical stimuli to the center of the excitatory field, resulted in responses to C-fiber activation being observed. This type of response was inhibited by applying a noxious thermal conditioning stimulus on the muzzle. The immersion of the muzzle in a 52 degrees C waterbath resulted in a strong reduction of the response during the application of the noxious conditioning stimulus and this was followed by long lasting poststimulus effects. Such inhibitory processes have been termed diffuse noxious inhibitory controls (DNIC). The effects on these inhibitions of lesions including the dorsolateral funiculus (DLF) were investigated in acute experiments: tests were performed before and at least 30 min after the DLF lesion. A lesion including the DLF ipsilateral to the neuron under study completely abolished the inhibitory processes triggered from the muzzle. Concomitantly, a facilitation of C-fiber responses was observed. Nevertheless, DNIC was still impaired even using a juxtathreshold current to elicit a weak C-fiber response. To ascertain further the main, if not entire, participation of the ipsilateral DLF in the descending projections responsible for the heterotopic inhibitory processes, the effects of a lesion of the contralateral DLF were investigated. Neither the inhibitory processes nor the unconditioned C-fiber responses were altered by this procedure. Again, a second lesion including the ipsilateral DLF induced a blockade of DNIC. It is concluded that the descending projections involved in the triggering of DNIC are mainly, if not entirely, confined to the DLF ipsilateral to the neuron under study. The contralateral DLF did not appear to play a role in these processes.
Short-latency ocular following responses of monkey. II. Dependence on a prior saccadic eye movement
Authors: Kawano K. , Miles F. A.
Published: December 2017

The ocular following responses elicited by brief unexpected movements of the visual scene were studied in eight rhesus monkeys. Test patterns were random dots except in one experiment when sine-wave gratings were used. Test stimuli were velocity steps of 100-ms duration applied after spontaneous saccades. Two response measures were used: the initial peak in the eye velocity profile (ei), and the average final eye velocity over the period of 110-140 ms measured from stimulus onset (ef). Responses were best when the test ramps began soon after saccades and attenuated progressively as the postsaccadic delay interval was increased: postsaccadic enhancement of ocular following. The decline in ei was roughly exponential: average time constant, 60 ms; average asymptote, 22%. Later measures (ef) were generally less affected. We suggest that this transient enhancement aids the visual suppression of postsaccadic ocular drifts (glissades) and the tracking of moving images newly acquired with a saccade. The magnitude of the postsaccadic enhancement was dependent on the amount of retinal stimulation during the antecedent saccade; when this stimulation was compromised, as when a vertical saccade was made while viewing a grating pattern with vertically oriented stripes, subsequent enhancement of ocular following was much reduced. Further, saccade-like conditioning movements of the visual scene resulted in an enhancement of the ocular following, elicited by subsequent test ramps, that was similar in magnitude and time course to that in the wake of real saccades. We conclude that the postsaccadic enhancement of ocular following is largely due to the visual stimulation produced by the saccade sweeping the scene across the retina. Data obtained with the visual field partitioned into central and peripheral regions (center 20-60 degrees diam) and with gaze centered suggested that the short-latency ocular following system and the enhancement mechanism that modulates it both receive their major inputs from the central 40 degrees of the retina. Further, when this central region was partitioned, enhancement was obtained only when the conditioning and test stimuli were presented to the same region of retina. Visual enhancement showed only weak interocular transfer: the conditioning and test stimuli had to be seen by the same eye to produce appreciable enhancement. These data suggest that the enhancement involves local spatial interactions at an "early" point in the visual pathway before the inputs from the two eyes have converged. When the conditioning and test stimuli impinged on different regions of the retina, brief powerful suppression of ocular following was obtained.(ABSTRACT TRUNCATED AT 400 WORDS)