bluuebunny/crossref_metadata_2025 huggingface dataset:
Increases in reflex excitability of monkey masseter motoneurons before a jaw-bite reaction-time response
Authors: Blair-Thomas C. A. , Luschei E. S.
Published: December 2017

Reflex excitability of the motoneurons innervating the masseter muscle of monkeys was tested before a phasic voluntary activation of the jaw-closing muscles (a RT bite response). Single test shocks were delivered to the Mes V which supplies a monosynaptic excitatory input to the jaw-muscle motoneurons. Changes in reflex excitability were assessed by measuring the amplitude of the synchronous muscle potential evoked by the test shock. Amplitudes of the muscle potentials evoked by shocks which occurred just before the beginning of the voluntary EMG response, as judged by the onset of EMG activity of the masseter muscle contralateral to the test shock were many times larger than potentials evoked immediately following the visual RT stimulus. Curves relating the average amplitude of the evoked response to its time before the beginning of the voluntary response suggest that the reflex excitability of the motoneuron pool begins to increase 25-45 ms before the first detectable EMG activity occurs. These results suggest that inputs arrive at the motoneurons of agonist muscles used in rapid RT tasks substantially before changes in the EMG of the muscle are noted. These results, in part, would account for the time interval noted between the beginning of neural activity in suprasegmental structures which presumably excites spinal motoneurons, and the first EMG activity of muscles which are innervated by these motoneurons.
Functional characteristics of superior olivary neurons to binaural stimuli
Authors: Moushegian G. , Rupert A. L. , Gidda J. S.
Published: December 2017

This investigation was undertaken to study the timing properties of low-frequency binaural neurons located in the medulla of kangaroo rat (Dipodomys spectabilis). The results show that the response variables, vector strength (VS) and discharge rate (DR), are not necessarily related responses; each may be conveying a different parameter of acoustic stimuli. The results also lead to the conclusion that binaural low-frequency neurons, whether they are excitatory-excitatory (EE) or excitatory-inhibitory (EI), in essence, function similarly. Finally, this investigation presents findings which suggest that a clock, which may be part of a mechanism for pitch as well as for spatial localization, is activated by sounds, providing thereby a reference signal for neural discharges.
Analysis of afferent responses from isolated semicircular canal of the guitarfish using rotational acceleration white-noise inputs. II. Estimation of linear system parameters and gain and phase spectra
Authors: O'Leary D. P. , Honrubia V.
Published: December 2017

Quantitative estimates were computed for exponential coefficients and rate constants contributing to afferent unit impulse responses obtained from bundles innervating specific regions of the semicircular canal. The grouping of these estimates into specific response classes provided quantitative correlations with specific anatomical regions of innervation of the crista. Linear system gain and phase spectra were computed also, by applying Fourier transformations to unit impulse responses, for purposes of comparison with previous studies employing frequency domain analyses. Responses fitted by third-order linear system equations were specific to afferents innervating the crest and transition regions of the crista; whereas those fitted by overdamped, second-order equations were specific to afferents innervating the slopes and transition crista regions.It was concluded that strictly mechanical models of the transduction process are inadequate to account for the diverse and spatially distributed classes of observed responses and, moreover, structural features such as different hair cell types or efferent innervation effects could be excluded as inoperative in this preparation. The alternative hypothesis was suggested that certain of the observed subcomponents could be direct reflections of the initial mechanical stimulus, but that other subcomponents were reflections of more complex filtering mechanisms operating at the cellular or synaptic levels.
Activity and excitability to electrical current of cortical auditory receptive neurons of awake cats as affected by stimulus association
Authors: Woody C. D. , Knispel J. D. , Crow T. J. , Black-Cleworth P. A.
Published: December 2017

1. Unit activity and excitability were studied at the midlateral and suprasylvian cortex of naive, blink-conditioned and "randomization" cats. The latter received the same CS and US as did the conditioned animals, but in random temporal order and with random intertrial intervals with mean comparable to that used for conditioning. The randomization group failed to develop a blink CR. 2. With conditioning, spontaneous and evoked unit discharges were increased above levels found in naive animals. Correspondingly, levels of extracellularly injected current required to elicit a spike discharge were lower in conditioned than in naive animals. In addition, in the conditioned animals, the degree of enhancement of evoked activity and excitability was found to be greatest in the units that responded to the CS, as opposed to units that responded to another auditory stimulus of equal intensity but of no special behavioral significance vis-a-vis the conditioned reflex. 3...
Effects of cerebellar lesions on saccadic eye movements
Authors: Ritchie L.
Published: December 2017

1. Areas of cerebellar cortex related to saccadic eye movements were ablated in three Macaca mulatta monkeys trained to fixate visual targets. There followed a postoperative dysmetria of saccadic eye movements which appeared to be the result of an impairment specifically within the saccadic system. 2. Convergent evidence from two experimental paradigms indicated that the saccadic deficit was a function of the position of the eye in the orbit and did not involve retinal error processing. 3. The pattern of this position-dependent dysmetria suggests that the eye was no longer fully compensating for the elastic restoring forces imposed by the orbital medium and antagonist muscle(s). 4. The similarity of these data to saccadic eye movements of human cerebellar patients and arm movements of rhesus monkeys with cerebellar lesions indicates that the inability to compensate for the differential loads placed on motor systems by the mechanics of those systems may explain several cerebellar symptoms.
Identification of two species of alpha motoneurons in cat's plantaris pool
Authors: Harris D. A. , Henneman E.
Published: December 2017

1. Single units of the plantaris pool were isolated in ventral root filaments of decerebrate cats and their critical firing levels (CFLs) were determined. Motoneurons of similar size, as judged by their CFLs and other criteria, were compared in firing rate (FR) during repetitive stimulation of the plantaris nerve. 2. Such units either differed very little or quite widely, suggesting that they were sampled randomly from two populations, one firing rapidly, the other slowly. The relationship between the two rates remained approximately constant, regardless of the intensity or rate of input the units received, as long as both of them discharged rhythmically. 3. In single experiments 10-15 of the smallest units in the pool (all with CFLs in the 0-8% range) were isolated and compared. Statistical analyses and visual inspection of these small samples again suggested the existence of two species of motoneurons. 4. Statistical analyses also indicated that the FRs of units in single experiments were not sampled from any one of a variety of parametric, single-modal distributions. This suggests that the data were sampled from a distribution having more than one mode, indicating the existence of separate populations or species of motoneurons among the small units of the pool (0-8% range of CFL). 5. Pooling of the normalized data from different experiments revealed a bimodal histogram, reinforcing the conclusion that there are two species of small alpha motoneurons in the plantaris pool.
Spontaneous slow potentials and spreading depression in amphibian retina
Authors: Olsen J. S. , Miller R. F.
Published: December 2017

1. In frog and mudpuppy eye cups perfused with low-chloride solution, two types of slow potential phenomena were studied. One type, "spontaneous slow potentials" (SSPs), appeared both in the dark and during light stimuli. The other type, the slow potential change (SPC) of spreading depression (SD), appeared at termination of long-duration light stimuli. 2. The SSPs were analyzed by depth-profile studies, pharmacologic studies, and the use of potassium-specific electrodes. Results indicated that SSPs may represent spontaneous d-waves that travel across the retina. The SSPs are associated with potassium activity, and the main response is probably generated by Muller cells. Initiation and/or propagation appear to require chemically mediated synaptic transmission and impulse activity. 3. Depth-profile studies were also done of the SPC of SD induced by termination of long-duration light stimuli. Results indicated that the SPC is not an exaggerated d-wave. The SPC consists of two components, the second of which reverses more superficially than the d-wave. The main SPC response is probably generated by Muller cells. Although impulse activity does not appear to be necessary for SD, it may contribute to this complex response.
Recruitment and suprathreshold frequency modulation of single extraocular muscle fibers in the rabbit
Authors: Barmack N. H.
Published: December 2017

1. The isometric tension developed by the inferior rectus muscle of the rabbit was modulated by the vestibuloocular reflex (VOR) in unanesthetized rabbits. 2. Single muscle fiber activity was recorded from the inferior rectus muscle during reflex activation. The force at which a muscle fiber was recruited and its suprathreshold frequency-force relationship were studied. 3. The size of individual motor units was measured by averaging the tension which was "time-locked" to the discharge of a single muscle fiber. The average motor unit twitch amplitude was 1.3 mg. 4. The suprathreshold frequency-force function was characterized by an initially steep slope, followed by a less steep slope, until a level of saturation was reached at higher forces. 6. Motor unit size was linearly related to recruitment threshold. Small motor units also had a significantly steeper frequency-force relationship than larger motor units. 7. The relationship between motor unit size and recruitment threshold appears to compensate for changes in the operating point on the length-tension curve of extraocular muscle.
A comparison of similar ionic responses to gamma-aminobutyric acid and acetylcholine
Authors: Yarowsky J. , Carpenter D. O.
Published: December 2017

1. Fast Na+-, Cl-, and K+-Conductance increase responses to gamma-aminobutyric acid (GABA) show times to peak similar to the comparable ionic responses to acetylcholine (ACh). 2. On some identified neurons, both putative transmitters elicit responses due to the same conductance change. For example, in cell R2 both substances cause an increase in Cl- conductance. Receptors for GABA and ACh on R2 do not cross desensitize and therefore are distinct. The ACh but not the GABA response is blocked by alpha-bungarotoxin and strychnine. 3. In R2 both responses reverse at -58 mV, and the Cl- ionophore (for both responses) appears to be partially permeant to propionate and isethionate, but impermeant to acetate, sulfate, and methylsulfate. 4. The Cl- responses but not the Na+ responses to both ACh and GABA are blocked by both picrotoxin and bicuculline, the classical GABA antagonists. 5. These results are compatible with the hypothesis that the ionophores associated with receptors to different neurotransmitters but mediating the same ionic conductance change have many common properties and may, in fact, be identical. Bicuculline and picrotoxin may be specific blockers of the Cl- ionophore, not the GABA receptor.
Controlled locomotion in the mesencephalic cat: distribution of facilitatory and inhibitory regions within pontine tegmentum
Authors: Mori S. , Nishimura H. , Kurakami C. , Yamamura T. , Aoki M.
Published: December 2017

1. The contribution of postural tonus to controlled locomotion elicited by the stimulation of mesencephalic locomotor region (MLR) was studied in the acute precolicular-postmammillary decerebrate (mesencephalic) cat. 2. A microelectrode was placed in the unilateral MLR and another was placed systematically at 1-mm increments throughout the pons (H--4 to H--1O) at level ranging from P2 to P11 dorsoventrally and mediolaterally from 0 to L or R6. Depending on the general condition of the animal, stimuli through this second electrode were delivered preceding, succeeding, or simultaneous with the MLR stimulation. 3. Stimulation of the ventral part of the caudal tegmental field (P3 to P9, H--6 to H--8) increased extensor tonus of the hindlimbs, as assessed by recording muscle activity. Concomitant stimulation of this region converted MLR-elicited hindlimb stepping to coordinated four-legged locomotion and also elicited locomotion even when stimulation of the MLR alone failed to elicit locomotion. Stimulation of this ventral tegmental region alone at a larger stimulus intensity elicited spastic locomotor movements associated with a substantial increase in extensor tonus. 4. Stimulation of the lateral tegmented field surrounding the pontine locomotor region (PLR) also facilitated MLR effects, but had a relatively weaker facilitatory effect on postural tonus then stimulation of the ventrocaudal tegmental field. PLR stimulation alone was also ineffective when postural tonus was not well maintained. 5 Stimulation of the dorsal part of caudal tegmental field (P3 to P9, H--4 to H--6) in its midline dramatically decreased extensor tonus of the hindlimbs. MLR-elicited controlled locomotion was completely suppressed during concomitant stimulation of this inhibitory region. 6. These results indicated clearly that the degree of existing postural tonus greatly affects MLR-elicited locomotor movements and that an increase in postural tonus and an activation of the spinal stepping generator are not separate phenomenia.
Effects of stimulating in raphe nuclei and in reticular formation on response of spinothalamic neurons to mechanical stimuli
Authors: McCreery D. B. , Bloedel J. R. , Hames E. G.
Published: December 2017

1. The purpose of these experiments was to compare effects of electrical stimuli applied in two regions of the brain stem that are the sites of origin of descending bulbospinal systems; namely, the nucleus gigantocellularis of Brodal (7) and the nucleus raphe magnus, on the responses of lumbosacral spinothalamic neurons to mechanical stimuli. 2. In cats anesthetized with alpha-chloralose, stimulating in either of these structures with single pulses of current while the spinothalamic neuron was tonically activated by a sustained mechanical pressure resulted in an increase in the excitability of the cell followed by a prolonged suppression of its impulse activity. 3. For different neurons, the latency of the excitation ranged from 4 to 18 ms following the brain stem stimulus, while the latency of the suppression ranged from 16 to 34 ms. 4. In general, the effects of stimulating in the reticular formation and in the raphe nuclei were similar. although quantitative differences were found in the effects of each on different spinothalamic neurons. On the basis of these two studies, it is argued that the reticulospinal and raphe-spinal systems exert qualitatively similar effects on the responses of spinothalamic neurons evaluated in this experiment. 5. A comparison of the magnitudes of the suppression phase evoked from several different sites in the ipsilateral reticular formation and nucleus raphe magnus suggests that the descending systems arising from both these structures may be quite heterogeneous. 6. Stimulation of both regions of the brain stem produced a much greater suppression of the response of the spinothalamic neurons to slowly changing or sustained mechanical stimuli than to transient stimuli. It is suggested that the effects of descending systems arising both in the raphe nuclei and in the reticular formation on the responses of spinothalamic neurons to a mechanical stimulus are at least as dependent on the time course of the mechanical stimulus as they are on its intensity.
Triggering of lordosis reflex in female rats with somatosensory stimulation: quantitative determination of stimulus parameters
Authors: Kow L. M. , Montgomery M. O. , Pfaff D. W.
Published: December 2017

1. Pressure on the skin of the tail base and perineum of female rats in the range of 40--440 millibars, following bilateral contact with the flanks, was adequate to elicit the lordosis reflex. Hair deflection alone or noxious stimulation was neither sufficient nor necessary for lordosis behavior to occur. 2. For a given pressure, increasing the area of stimulation increased the effectiveness for evoking lordosis; inputs from mechanoreceptors at different skin locations can be summated to trigger the behavioral response. 3. During mating behavior, increased pressure from the male rat on the skin of the female, in the range of 50--450 millibars, was associated with increased probability and strength of lordosis. 4. Increasing the dose of estrogen increased the probability of lordosis to a given pressure stimulus. The hormone effect can be characterized as a facilitation of the throughput from low-threshold pressure receptors on tail base and perineum to motoneurons for the lumbar vertebral dorsiflexion of lordosis.
Photoreceptor coupling in retina of the toad, Bufo marinus. I. Anatomy
Authors: Gold G. H. , Dowling J. E.
Published: December 2017

1. Red rod photoreceptors in the toad retina, which are known to be physiologically coupled, were examined for interreceptor contacts. 2. A dense network of large gap junctions was found between the inner segments of red rods, this being the only specialized site of contact that was observed between rods. Each red rod contacts an average of about four neighboring red rods with a junctional area of approximately 0.75 micrometer2. From freeze-fracture micrographs, the density of junctional particles was found to be 5 X 10(3)/micrometer2. 3. The large gap junctions were found only to connect red rods to each other in agreement with physiological data. Only small focal gap junctions were seen between red rods and cones and no junctions were observed between red and green rods. 4. It is concluded that these gap junctions are the site of coupling between the red rods and that the coupling is electrical.
Electrotonic coupling among neuroendocrine cells in Aplysia
Authors: Blankenship J. E. , Haskins J. T.
Published: December 2017

1. We have discovered and characterized direct electrotonic synaptic coupling among a population of neuroendocrine (bag) cells in the parietovisceral ganglion of the marine gastropod Aplysia dactylomela. Pairs of ipsilateral and contralateral bag cells were impaled in vitro with microelectrodes. Current pulses applied through the electrometer amplifier to either cell influenced the other cell via electrotonic connections. 2. The coupling between bag cells was relatively weak when measured at the somata; the mean ratio of postsynaptic/presynaptic response amplitudes is 0.0075. Junctional rectification was not detected. The latency between pre- and postjunctional responses was long, up to 50 ms, a delay comparable to that for chemical synaptic transmission among neurons in this ganglion. Low-Ca2+/high-Mg2+ bathing solutions did not block transmission between bag cells, but did block chemical synaptic potentials in other identified neurons. 3. Postjunctional electrotonic responses had markedly slow time courses compared to the prejunctional responses, a characteristic that permitted summation of otherwise undetectable electrotonic PSPs and the demonstration of coupling between the two (bilateral) clusters of bag cells. 4. Based on extracellular recordings of their compound action potentials, the neurites of A. dactylomela bag cells extended a shorter distance (approximately 3 mm) along the connective than the neurites of A. californica or A. brasiliana. 5. Electrolytic lesions made along the neurites during intrasomatic coupling measurements significantly shortened the duration of postjuctional electrotonic responses, indicating that the neurites are widely electrically interconnected and, as a population, have a large effective membrane capacitance. The lesions furthermore revealed that an important site of electrotonic coupling is at the base of the pleurovisceral connective just rostral to the bag cell cluster. 6. The small-amplitude, long-latency and prolonged time course of postjunctional responses are interpreted to indicate remote and widespread coupling sites among the bag cells. This electrotonic coupling underlies the synchronized firing of the bag cells.
Electrical interaction between motoneurons and afferent terminals in cat spinal cord
Authors: Curtis D. R. , Lodge D. , Headley P. M.
Published: December 2017

1. The electrical threshold of the terminations of single group Ia and II afferent fibers was transiently reduced by the antidromic discharge of the initial segment of spinal motoneurons in the cat. 2. This depolarization of the terminals of afferent fibers known to synapse on motoneurons confirms previous observations of antidromic electrical interaction between these structures.
Multiple, prolonged actions of neuroendocrine bag cells on neurons in Aplysia. I. Effects on bursting pacemaker neurons
Authors: Mayeri E. , Brownell P. , Branton W. D. , Simon S. B.
Published: December 2017

1. The bag cells are a group of neuroendocrine cells located in the abdominal ganglion of Aplysia. Accumulated evidence suggests they synthesize and release egg-laying hormone (ELH), a peptide that induces egg laying. In this and the following paper (37) we describe five types of prolonged neural responses in cells of the isolated abdominal ganglion that are produced by stimulated bag cell activity. 2. Prolonged, 5- to 40-min bursts of spike activity were triggered in the normally silent bag cells by local stimulation of one of the bag cell clusters with brief, 0.6- to 2-strains of pulses. This local stimulation minimized the possible effects of the stimulus on other ganglion cells and initiated bag cell activity similar to what has been recorded in intact animals at the initiation of egg laying. 3. Following onset of triggered bag cell activity there is an increase in the amplitude of the bursting pacemaker potential in cell R15 that results in augmented bursting activity in this autoactive cell for up to 3 h. The increase begins in less than 1 min and reaches a maximim after 8--20 min. In two other bursting pacemaker cells, L3 and L6, there is a second type of response, slow inhibition, consisting of a smoothly graded hyperpolarization that begins in 5--14 s, reaches a peak value of 10--20 mV after 30 s, and results in a decrease in the spontaneous spike activity of these cells for 3 h or longer. Both types of responses are contingent on the occurrence of bag cell activity, they depend on prolonged bag cell activity for their normal expression, and they occur in the absence of the fast interactions characteristic of conventional synapses. 4. The results reveal at the level of intracellular recordings prolonged actions of peptide-secreting neuroendocrine cells on the central nervous system. The role of ELH as a putative mediator of one or more of these actions is discussed.
Neuronal correlates of siphon withdrawal in freely behaving Aplysia
Authors: Kanz J. E. , Eberly L. B. , Cobbs J. S. , Pinsker H. M.
Published: December 2017

1. Central neuronal mechanisms of siphon withdrawal in Aplysia were studied for the first time in intact, freely behaving animals by means of population recordings from implanted whole-nerve cuff electrodes. Intracellular follow-up studies were then conducted when the same animal was reduced to a semi-intact preparation. 2. Background spontaneous activity in the siphon nerve consisted of low-frequency firing of a population of efferent units containing identified siphon motoneurons. 3. Spontaneous patterned bursts of efferent activity occurred irregularly and were associated with all-or-nothing contractions of the parapodia, gill, and siphon. Spontaneous bursts were due to centrally generated activity in the interneuron II (INT II) network, an oscillatory network with endogenous pacemaker properties. 4. In intact animals, even weak tactile stimuli to the siphon typically triggered an INTII burst shortly after the stimulus-locked efferent activity. Thus, the stimulus can phase-advance the INT II oscillator. In semi-intact preparations, short-latency INT II bursts were triggered less less frequently and required more intense stimuli. 5. With weak to moderate-intensity stimuli in intact animals, the presence of short-latency triggered INT II bursts largely determined the duration of the siphon component and amplitude of the gill component of the withdrawal reflex. 6. When stimuli were repeated over a range of interstimulus intervals (from 60 to 1 min), the likelihood of triggering a short-latency INT II burst die not change systematically. Thus, the ability of the siphon stimulus to stably entrain the all-or-none INT II component over a wide range of intervals will interact behaviorally with the decrement of the monosynaptic component of the reflex with repetition.
Responses of lumbosacral spinal units to mechanical stimuli related to analysis of lordosis reflex in female rats
Authors: Kow L. M. , Zemlan F. P. , Pfaff D. W.
Published: December 2017

1. To analyze further the sensory mechanisms for triggering the lordosis reflex, single-unit (n = 345) activity was recorded extracellularly from spinal segments L5-S1 of urethan-anesthetized female rats. Unit responses to pressure on the skin (necessary and sufficient for evoking lordosis) and other mechanical stimuli were studied. 2. Units were classified according to their responses to the battery of mechanical stimuli: 16% of the units responded only to pressure. The majority of these pressure-responsive units were excited, while a few were inhibited or responded differently, depending on the site stimulated; 52% did not respond to pressure, but responded to brushing, muscle-joint, and/or visceral stimulation, or did not respond at all. The remaining 32% responded to pressure plus other forms of stimulation. 3. Units responding only to the movement of individual types of hair tended to be located in the dorsal horn, more dorsal than units responding only to pressure (found primarily in the intermediate gray). Units responding to subdermal stimulation were usually found at greater depths. Segmental and somatotopic distributions of spinal units observed were very similar to those reported for cat (3) and monkey (5). 4. Compared to primary sensory units (28), spinal units had higher resting firing rates, more complicated responses to a given stimulus, a wider variety of unit types, and much larger receptive fields. These comparisons tend to indicate convergence of primary sensory neurons onto individual spinal units. 5. The range of pressure thresholds of pressure-responsive units is comparable to the range effective for triggering lordosis. We postulate that excitation of units responding only to pressure is centrally involved in triggering the lordosis reflex. Those units not responding to pressure are probably irrelevant for this behavior. Presently undetermined are the roles of units with complex or mixed-response types.
Motor controls of opaline secretion in Aplysia californica
Authors: Tritt S. H. , Byrne J. H.
Published: December 2017

1. Using combined morphological and electrophysiological techniques, we have identified motor neurons in the right pleural ganglion of Aplysia californica that contribute to the release of opaline from the opaline gland. 2. Three pleural ganglion neurons were found to meet the requirements for identification as opaline gland motor neurons by a) sending processes in nerve P5, which innervates the gland; b) producing contractions of the gland in the absence of central synaptic activity; and c) producing excitatory junctional potentials (EJPs) in cells making up the opaline gland itself. The neurons can be reliably located and have been designated PLR1, PLR2, and PLR3. 3. When gland contraction is measured by the change in luminal pressure, the gland response is a graded function of low-frequency spike activity in the motor neurons. 4. Presumptive EJPs recorded from opaline gland cells are reversibly decreased in size by high extracellular Mg2+ and reversibly increased in size by raising the concentration of extracellular Ca2+. These results suggest that the presumptive EJPs are chemically mediated. The presumptive EJPs show facilitation and posttetanic potentiation. 5. The identified opaline motor neurons may constitute a significant portion of the motor input to the opaline gland via nerve P5 since hyperpolarization of the cells prevents the opaline gland response elicited by right connective stimulation in vitro. 6. We have compared the properties of the opaline motor neurons with the previously identified properties of the ink motor neurons (6--9, 19). Like the ink motor neurons, the opaline motor neurons have high resting potentials, are electrically coupled, and have no spontaneous spike activity. They also receive a slow and long-lasting evoked depolarizing synaptic input, which appears to be mediated by a decreased conductance mechanism. The firing pattern of the opaline motor neurons produced by synaptic input shows the same delayed bursting pattern previously described for the ink motor neurons. 7. The biophysical properties and synaptic input to the ink motor neurons have been shown to affect the features of inking behavior (4, 6--9, 19). The opaline motor neurons share some of these biophysical characteristics and mediate a defensive behavior similar to ink release. Further comparisons of these behaviors and their underlying neural circuits may provide a better understanding of the extent to which cellular biophysical properties and patterns of synaptic input influence the features of the behaviors that individual neurons mediate.
Patterns of responses of neurons in cuneate nucleus to controlled mechanical stimulation of cutaneous velocity receptors in the cat
Authors: Golovchinsky V.
Published: December 2017

1. The responses of single cuneate neurons to controled mechanical stimulation of skin were recorded in cats lightly anesthetized with a nitrous oxide-halothane mixture. The discharge patterns and peripheral receptive-field characteristics were studied in neurons driven by sensitive cutaneous mechanoreceptors, including slowly adapting skin mechanoreceptors. Virtually all cuneate neurons display maximum discharge during the velocity component of displacement. 2. Among cuneate neurons encountered in this study, approximately 46% were driven by guard hair mechanoreceptors, 15% were driven by field receptors, and 13% were driven by slowly adapting skin receptors. Neurons responding to stimulation of deep tissues (including claws) were not studied with controlled mechanical stimulation and accounted for 19%. The rest of the neurons were driven by Pacinian corpuscles, received afferent inputs from several different first-order afferents, or were not definitely identified. There was no clear evidence of down hair or high-threshold mechanoreceptor representation. 3. The discharge pattern in response to a constant-velocity stimulus proved most valuable in describing submodality classes of neurons driven by hair and field receptors since sensitivity of these neurons to dynamic and to static phases of stimulation constitute respective continua and, thus, preclude sharp separation into distinct groups. 4. The majority of neurons displayed response properties and receptive fields similar to those of first-order afferents. A minority of cells had receptive fields that were larger than those of primary afferents, with nearly identical modality and velocity characteristics throughout the receptive field. 5. Approximately 2% of recorded neurons displayed convergent properties not encountered in first-order afferents, including neurons driven from receptors of different modalities or from discontinuous receptive fields. 6. Inhibition of neuronal firing generated from outside the receptive field was rarely seen, possibly due to anesthetic conditions. In a small number of neurons, irregularities in the discharge were observed that might indicate inhibitory influences originating from within the receptive field.
Influence of raphe nuclei on neuronal transmission from perforant pathway through dentate gyrus
Authors: Winson J.
Published: December 2017

1. In chronically prepared, freely moving rats, electrical stimulation was applied to the perforant pathway and monosynaptic responses were recorded extracellularly in the ipsilateral dentate gyrus. In some tests a stimulus was also applied to the median raphe nucleus (mr) prior to activating the perforant pathway. Experiments were performed during two behavioral conditions: slow-wave sleep (SWS) and the still, alert state (SAL). Two varieties of evoked responses were recorded: those due to synchronous firing of neuronal action potentials (evoked action potentials or EAPs) and those produced by excitatory synaptic activity (evoked synaptic potentials or ESPs). 2. As reported previously (38), perforant path stimulation elicited EAPs of greater magnitude during SWS than during SAL. The application of a prior stimulus to mr (prestimulation) markedly increased the already elevated EAPs observed during SWS. The EAPs during SAL were unaffected by prestimulation. 3. The minimum delay time (time between mr and perforant path stimuli) at which the augmentation of the EAPs appeared during SWS was approximately 5 ms. The augmentation reached a maximum at delay times of 25-40 ms and was present up to a delay time of 150 ms. 4. As in former experiments (38), ESPs recorded in the molecular layer of the dentate gyrus after perforant path stimulation were found to be greater during SAL than during SWS. Prestimulation of mr had no significant effect on the ESPs at any level of the molecular layer during either SWS or SAL. 5. The perforant path afferent volley was recorded at high gain in the dentate gyrus. Its amplitude was found to be solely dependent on perforant path stimulus intensity and not on behavioral state or the prestimulation of mr. 6. In preparations anesthetized with Chloropent (82% chloral hydrate, 18% pentobarbital; Fort Dodge Laboratories, Fort Dodge, IA), prestimulation was applied at each of a number of loci within the pons and medulla, including mr, As in SWS, prestimulating mr resulted in augmented EAPs with a minimum delay time of 5 ms. Similar augmented responses were observed when stimulation was applied at other raphe nuclei (dorsal raphe, pontis, magnus, and pallidus), but there was no augmentation when stimulation was applied at other brain stem sites. Threshold stimulus intensities for producing augmented EAPs in the raphe nuclei were less than 30 microA. 7. In freely moving animals it was first established that the EAP responses during SWS were markedly greater than during SAL. Midline lesions were then made at the rostrocaudal level of mr. Following the lesions, there was no longer any significant difference in the magnitude of the EAPs recorded during the two behaviors. 8. These findings suggest that tonic influences arising from raphe nuclei during SWS may be involved in the facilitation of neuronal transmission through the dentate gyrus observed during this behavioral state.
Response of forelimb guard hair afferent units to air-jet stimulation of entire receptive field
Authors: Goldfinger M. D. , Amassian V. E.
Published: December 2017

1. In anesthetized, immobilized cats, individual axonal responses to movement of forelimb G hairs were recorded in the ipsilateral cuneate fasciculus at C1-C2 with a glass-insulated tungsten microelectrode. Several test criteria were used to identify primary afferent axons among the recorded neurons. 2. The output discharge in the parent sensory axon during continuous air-jet stimulation of the entire receptive field was irregular and was usually maintained. Criteria for statistical stability were introduced, permitting an analysis of the response as a stable point process. 3. The main interspike interval during the response to maximal air-jet stimulation ranged in different units from 4 to 100 ms, with a transition zone near 20 ms (50/s) between short and long mean interval units. Long and short mean interval units tended to be related to G2- and G1-type hair receptors, respectively. 4. In both short and long mean interval units, the interspike-interval distribution (IID) had a dead time (usually 2-4 ms), a sigmoidal rising limb, a single mode, and a monotonic falling limb, a single mode, and a monotonic falling limb. In short mean interval units, the decrement of the falling limb was described by a single exponential. 5. The value of the standard deviation of the IID was a little less than that of the mean interval minus dead time, the inequality probably resulting from the finite duration of the rising limb and, in long mean interval units, the nonexponential falling limb. 6. Joint interval analysis revealed that successive intervals were independent except in short mean interval units, where the shortest intervals tended to be followed by intervals shorter than the mean. 7. The expectation density function did not reveal any periods in the output discharge. In short mean interval units, a constant mean (planteau) level was attained after a finite rise time and usually one or more overshooting-undershooting sequences. In long mean interval units, the expectation density function monotonically rose to the plateau level. 8. Reducing the air-jet intensity caused an increase in mean interval of discharge and in standard deviation of the IID and slowed the rise time of the expectation density function to the plateau level. 9. Similarities and differences between the whole-field response to air-jet stimulation and the Poisson process are discussed.
Characteristics of saccadic dysmetria in monkeys during reversible lesions of medial cerebellar nuclei
Authors: Vilis T. , Hore J.
Published: December 2017

1. The accuracy of saccadic eye movements made by trained Cebus monkeys was studied during reversible lesions produced by cooling through probes implanted between the interpositus and fastigial nuclei (medial probe) or lateral to the dentate nucleus (lateral probe). 2. Cooling through the lateral probe did not impair the accuracy of vertical or horizontal saccades, However, cooling through the medial probe produced a dysmetria whose magnitude was dependent on the position of the eye and on the direction of the saccade. 3. The amplitude/duration relation of dysmetria saccades was not significantly different from that of normal saccades. 4. The trajectories of the horizontal and vertical components of oblique saccades remained essentially straight during medial probe cooling in spite of unequal dysmetria in the two components. This suggests that the mechanism that produces a dysmetria in one component must interact with the gaze center that determines the duration of the other component. 5. Cerebellar nuclear cooling through either lateral of medial probes did not alter the saccadic reaction time to a randomly timed step change in target position. This result differs from that found for limb movements where cerebellar dysmetria was associated with increased reaction times. 6. These results provide evidence that the cerebellum through the medial nuclei normally plays a role in terminating, but not in initiating, saccades.
Myoelectric responses at flexors and extensors of human wrist to step torque perturbations
Authors: Jaeger R. J. , Gottlieb G. L. , Agarwal G. C.
Published: December 2017

1. Torque-step perturbations were applied to flex or extend the wrists of normal human subjects. The electromyographic activity (EMG) of two of the stretched muscles, flexor carpi radialis and extensor carpi radialis, was monitored. 2. Based on functional characteristics and temporal bursting patterns, the EMG responses were partitioned into four distinct temporal intervals : 30-60, 60-120, 120-200, and greater than 200 ms after the onset of the torque step. The last interval continues for the duration of the step input: 200- 400 ms was chosen to represent activity in this interval. 3. EMG responses in the first two intervals show short, stable latencies and amplitudes that depend on the level of muscle contraction prior to the torque step. They are facilitated by any instruction requiring a reaction by the subject. They are reflexes that cannot be voluntarily suppressed by instruction to the subject. 4. The third EMG response is a triggered response. It is not a reflex because its appearance or absence is absolutely under voluntary control. Unlike true voluntary responses, there exists no dichotomy in responses latency or variability between known versus unknown directions of torque steps. 5. We consider that a truly voluntary response to a torque perturbation does not begin until about 200 ms after the step, which is on the order of visual or auditory reaction times. 6. The EMG responses were similar in both the wrist flexor and extensor studied. Ankle flexors and extensors do not show such similarity. 7. The EMG responses at the wrist and ankle are compared and shown to have many similarities. A general scheme for their classification is discussed.
Exogenous choline augments transmission at an identified cholinergic synapse in terrestrial mollusk Limax maximus
Authors: Barry S. R. , Gelperin A.
Published: December 2017

1. A variety of pharmacological tests indicate that the neuromuscular junction between the salivary burster neuron (SB) and the salivary duct muscle (SD) in the terrestrial mollusk Limax maximus is cholinergic. These include the effects of curare, atropine, and hexamethonium. 2. Exogenously applied choline can act both presynaptically and postsynaptically at the synapse between the SB and SD. a) When the SB-SD synapse is bathed in 30 microM choline, there is no measurable direct postsynaptic effect at the SB-SD synapse. After several hours of choline incubation, however, an increase is observed in the size of SB-elicited junction potentials recorded from the SD. b) When the synapse is bathed in 300 microM choline, a short-term decrease is seen in the amplitudes of junction potentials (JPs) recorded from the SD. This effect is interpreted as competition between choline and acetylcholine (ACh) for postsynaptic receptor sites on the SD, since the response of the denervated SD to ACh is diminished in the presence of 300 microM choline. c) After several hours incubation in 300 microM choline, the amplitudes of JPs elicited by the SB on the SD increase. 3. The long-term effect of exogenous choline is blocked by the choline-uptake inhibitor, hemicholinium 3. 4. We conclude that exogenous choline is taken up by the presynaptic terminals of the SB and converted to ACh. Transmitter output rises with growing transmitter stores, producing an increase in the size of SB-elicited JPs recorded from the SD.
Physiological properties of neurons projecting from area 3a to area 4 gamma of feline cerebral cortex
Authors: Asanuma H. , Waters R. S. , Yumiya H.
Published: December 2017

1. The corticocortical projection from area 3a to area 4 gamma was restudied using tranquilized cats. 2. Intracortical microstimulation (ICMS) of a given locus in area 3a produced effects on neurons in area 4 gamma that were located in a small area extending along the direction of the radial fibers constituting a columnar shape. 3. Cortical neurons in area 3a that projected to a particular neuron in area 4 gamma were located in a region that extended along the direction of the radial fibers and constituted a columnar shape. 4. Two-thirds of the projection neurons in area 3a had different receptive fields from those of neurons in the projected area in 4 gamma, thus suggesting that the 3a neurons are not simply transferring peripheral information to the 4 gamma neurons. 5. ICMS delivered to area 3a rarely excited 4 gamma neurons but rather facilitated their evoked discharges. 6. It is suggested that the activity of corticocortical projection from area 3a to 4 gamma can influence the activity of 4 gamma neurons only when combined with other inputs to the motor cortex.
Site of action of sleep-inducing muramyl peptide isolated from human urine: microinjection studies in rabbit brains
Authors: Garcia-Arraras J. E. , Pappenheimer J. R.
Published: December 2017

1. Sleep-promoting muramyl peptide purified from human urine (SPU) was injected through chronically implanted guide tubes into defined regions of the basal forebrain and brain stem of unanesthetized rabbits. Electroencephalogram (EEG) and body movements were recorded subsequent to each injection. 2. Of 52 injection sites, there were 8 in which microinjection of SPU induced significant increases of slow-wave sleep (SWS) for 5 or more hours. Each active site was tested twice with SPU and once with vehicle control. 3. Seven of the active sites were located in a region extending from the basal forebrain at the level of the optic chiasm to the mesodiencephalic junction. No active sites were found in the lower brain stem. 4. The behavioral and EEG characteristics of the excess SWS induced by microinjection of SPU appeared normal and similar to the excess sleep that follows intraventricular infusions of sleep factor. However, the responses occurred sooner after injections into an active site than after infusion into a lateral ventricle.
Generation and coordination of heartbeat timing oscillation in the medicinal leech. I. Oscillation in isolated ganglia
Authors: Peterson E. L.
Published: December 2017

1. The interactions among the four pairs of interneurons (HN(1)-HN(4)) of the heartbeat timing oscillator are confined to the third and fourth ganglia (G3 and G4). In isolation, G3 and G4 each produces a rhythm essentially the same as that shown when the two ganglia are linked together. 2. The local circuits in both ganglia have the same general form. In both the oscillation centers on a bilateral pair of HN cells that are linked by reciprocal inhibition (the HN(3) pair in G3 and the HN(4) pair in G4). In addition, there is reciprocal inhibition between an HN(3) or HN(4) cell and the intersegmental processes of the ipsilateral HN(1) and HN(2) cells. 3. These connections account for the phase relationships in an isolated G3 or G4, since cells linked by reciprocal inhibition produce bursts in alternation. 4. In isolated ganglia, reciprocal inhibition not only coordinates the activity of the HN cells but also appears to help generate their bursts. 5. Yet reciprocal inhibition alone cannot account for the activity of the network. An endogenous property of the HN(3) and HN(4) cells appears to create the instability necessary for oscillation.