bluuebunny/crossref_metadata_2025 huggingface dataset:
Gustatory neuron types in hamster brain stem
Authors: Smith D. V. , Van Buskirk R. L. , Travers J. B. , Bieber S. L.
Published: December 2017

In general, mammalian taste neurons are broadly responsive to stimuli representing different taste qualities. In the hamster, this breadth of tuning increases systematically from peripheral to successively higher brain stem neurons. Some investigators have classified taste-responsive neurons into "best-stimulus" categories on the basis of which of the four basic stimuli (sucrose, NaCl, HCl, or quinine hydrochloride) elicits the maximum response. However, attempts by others to demonstrate the existence of taste neuron types in the chorda tympani nerve and medulla of the rat using hierarchical cluster analysis have not been successful, resulting in the conclusion that there are no neuron types in the rat gustatory system. The present study was designed to look at the question of neuron types in the hamster, a species with a broader range of gustatory sensitivities to anterior tongue stimulation. Responses of 30 neurons in the nucleus tractus solitarius (NTS) and 31 neurons in the parabrachial nuclei (PbN) of the hamster to an array of 18 stimulus compounds were recorded extracellularly. The similarities of the neural response profiles of these cells at each synaptic level were compared using multivariate statistical techniques. The possiblee grouping of cells on the basis of similarities in their response functions was examined with hierarchical cluster analysis, and the relationships among these response functions were examined with multidimensional scaling. The results of the cluster analysis suggested that at both the NTS and PbN, there are three clusters of neural response profiles. These three clusters of response profiles are characterized at both synaptic levels by their predominant sensitivity to 1) sucrose and other sweet-tasting compounds, 2) sodium salts, and 3) nonsodium salts and acids. Representation of these neurons in a two-dimensional space yielded three nonoverlapping groups of cells in both the NTS and PbN, corresponding to the three groups identified by the hierarchical cluster solution. Classification of taste neurons either by their best stimulus or by other criteria has been criticized on the grounds that it may constitute an arbitrary division of a continuous population of neurons. The techniques of numerical taxonomy, which take the cells' variability into account, also result in a grouping of taste cells into classes. These taxonomic classes agree in most instances (80% in NTS and 80.6% in PbN) to a best-stimulus classification. The failure of some investigators to find types of neural response profiles in the rat gustatory system may be the result of species differences in taste sensitivity as well as differences in the statistical procedures employed.
REM sleep burst neurons, PGO waves, and eye movement information
Authors: Nelson J. P. , McCarley R. W. , Hobson J. A.
Published: December 2017

Pontogeniculooccipital (PGO) waves appeared almost simultaneously in both lateral geniculate nuclei (LGB), but in each case on had a larger amplitude and preceded the other by a few milliseconds. The larger, earlier wave is called the primary wave. Primary waves were found to appear with equal frequency in each LGB. During rapid eye movement sleep (REM sleep), LGB primary waves were ipsilateral to the direction of rapid eye movements. During REM sleep a group of cat midbrain neurons, which we call PGO burst cells, fired in stereotyped bursts at fixed latencies before ipsilateral primary waves, but they almost never fired bursts when the primary waves were contralateral. PGO burst neuron discharge also correlated with the direction of rapid eye movements during REM sleep. In wakefulness, PGO burst cells fired single spikes, not bursts, which had some correlation with LGB waves when averaged by computer. The results suggest that PGO burst cells are output elements in the PGO wave-generation system ad that PGO waves convey eye movement information to the sensory visual system in REM sleep. They also may have a role in the production of saccade-related waves in the visual system during wakefulness.
Visual cortical inputs to deep layers of cat's superior colliculus
Authors: Berson D. M. , McIlwain J. T.
Published: December 2017

In the superior colliculi of cats anesthetized with ketamine, 84% of identified output cells of the deep layers could be driven by shocks to the contralateral optic disk, optic chiasm, or ipsilateral optic tract; 75% of these deep-layer cells had response latencies reflecting a polysynaptic influence of retinal Y-cells. Following large, acute lesions of the ipsilateral occipital cortex (including visual areas 17, 18, 19, and the posteromedial lateral suprasylvian area (PMLS), only 18% of deep-layer output cells were driven by electrical stimulation of the optic pathway and only 4% exhibited an indirect Y-cell influence. Thus, one or more of these visual areas may be important for the relay of retinal information, and particularly of Y-cell information, to the deep layers of the superior colliculus. This hypothesis is supported by the observation that intracortical stimulation in areas 17, 18, 19, and PMLS activated many cells of the ipsilateral, deep tectal layers at latencies consistent with those exhibited by the indirect Y-cell pathway. The distributions of activation latencies were similar to those observed in the superficial layers, raising the possibility that at least some of the cortical influence on the deep layers may be mediated by direct connections. Cells of the deep layers were more likely to be excited by a cortical stimulus that activated cells immediately above them in the superficial layers than by a stimulus that did not. This indicates that the functional connections between visual cortex and the deep collicular layers exhibit a topographic orderliness similar to that previously described for corticotectal projections to the superficial layers. These results provide further evidence that the visual cortex exerts a significant influence on cells of the deep collicular strata and that the pathways involved are capable of mediating the indirect, retinal Y-cell input to these neurons.
Neural responses elicited by stimuli associated with masking of low-frequency, monaural tonal signals by noise
Authors: Langford T. L.
Published: December 2017

The responses of low-frequency, primary-like neurons of the ventral cochlear nucleus were measured as a function of signal-to-noise ratio for gated tonal signals and noise maskers that were varied in bandwidth and duration. For a given signal-to-noise ratio, each of the maskers is known to produce the same amount of masking in psychophysical experiments. The neural discharge rates measured in the present experiment were different, however, for each of the maskers for each signal-to-noise ratio. In contrast, all three maskers produced the same orderly relationship between signal-to-noise ratio and the degree of neural synchrony to the signals. It is concluded that information concerning the presence and relative strength of a low-frequency tonal signal in a background of masking noise is carried by the nervous system as the degree to which responses are synchronized to the phase of the signal.
Neuronal mediation of cardiovascular effects of food arousal in aplysia
Authors: Koch U. T. , Koester J. , Weiss K. R.
Published: December 2017

Previous studies have demonstrated that heart rate and blood pressure increase in Aplysia during an arousal state elicited by food stimuli. In addition, during biting, blood flow is routed alternately to the head (during protraction of the buccal mass) and to the digestive system (during retraction). In this study, cutting the pleuroabdominal connectives eliminated 75% of the heart rate response during food arousal, and cutting the pleuroabdominal connectives eliminated 20-50% of the pressor response. Recording in the abdominal ganglion from the RBHE heart excitor and the three LBVC vasoconstrictor motor neurons in a reduced preparation showed that activity in these neurons was increased 50 and 100%, respectively, during food arousal. Activity of the LBVC cells was maximal during the protraction phase of biting. The LBVC vasoconstrictor motor neurons, when fired at the rates recorded during food arousal, can occlude the abdominal aorta completely. We conclude that the RBHE and LBVC neurons mediate, in part, the heart rate and pressor responses recorded during food arousal and that cyclic activity in LBVC contributes significantly to the cyclic alternation of blood flow between the head and the gut during rhythmic biting behavior.
Cerebellar cortical activity during antagonist cocontraction and reciprocal inhibition of forearm muscles
Authors: Frysinger R. C. , Bourbonnais D. , Kalaska J. F. , Smith A. M.
Published: December 2017

Monkeys were trained to perform a maintained isometric grip of the thumb and forefinger that elicited a simultaneous cocontraction of the antagonist muscles of the forearm. The same monkeys were also trained to flex and extend the wrist against a stop with the fingers extended and to maintain an isometric wrist position for 1.0-1.5 s. During wrist movement, some of the synergist forearm muscles contracted during both flexion and extension. However, during the maintained isometric wrist position, the prime mover and synergist muscles were reciprocally active or silent. In the culmen-simplex region of the cerebellar cortex bordering on the primary fissure, 62% of the Purkinje cells that were identified by the climbing fiber discharge and that changed firing frequency decreased activity during maintained prehension. Almost all of these same Purkinje cells were reciprocally active during isometric wrist flexion and extension, although three neurons had similar discharge patterns during movements in both directions. In contrast, 79% of the unidentified neurons recorded from the same region of the cerebellar cortex increased discharge frequency during prehension. In general, most of these same neurons had reciprocal patterns of discharge during wrist movement even though a few cells were active during the dynamic phase in both directions. Together, the Purkinje cells and the unidentified neurons with bidirectional response patterns were thought to be related to muscles active during both flexion and extension wrist movements. No cells were found that increased discharge with the static isometric wrist torque exerted in both directions. The discharge frequency of some Purkinje and some unidentified neurons could be shown to be related to prehensile force as well as wrist movement velocity and isometric wrist torque. These data suggest that the discharge of about two-thirds of the Purkinje cells related to forearm muscles located along the borders of the primary fissure may depend on whether antagonist muscles are activated reciprocally or coactively. As a consequence, these cells may play a role in the selection or alternation between either of these two modes of muscular contraction. The increased discharge of the remaining one-third of the Purkinje cells excited during antagonist coactivation may provide inhibition of nuclear cells to stabilize the posture at joints other than the wrist and fingers or, alternatively, they may act to reduce nuclear cell discharge in proportion to the intensity of cutaneous stimulation.
Anatomical and functional organization of pathway from superior colliculus to lateral posterior nucleus in hamster
Authors: Mooney R. D. , Fish S. E. , Rhoades R. W.
Published: December 2017

A series of anatomical (autoradiographic and horseradish peroxidase, HRP) and electrophysiological experiments were carried out to determine the organization of the pathway from the superior colliculus (SC) to the lateral posterior nucleus (LP) in the hamster. Small, electrophoretic HRP deposits restricted to LP labeled numerous cells in both the ipsilateral and contralateral colliculus. Over 95% of the labeled cells were located in the lower one-half of the stratum griseum superficiale (SGS) and the upper stratum opticum (SO). A number of different morphological cell types contributed axons to the tecto-LP pathway. The receptive-field properties of antidromically activated tecto-LP neurons were delineated using extracellular single-unit recording techniques. Ninety-eight percent of the tecto-LP cells recorded were isolated in the SGS and SO. All tecto-LP cells responded more vigorously to moving than to flashed stimuli, one-third were directionally selective, and one-third exhibited some degree of speed selectivity. The responses of tecto-LP neurons did not differ appreciably from those of superficial layer collicular cells that could not be antidromically activated by LP shocks. Small pressure injections or electrophoretic deposits of [3H]leucine into sites with known retinotopy in the superficial collicular laminae were used to determine whether or not the tecto-LP projection in hamster was topographically organized. Injections anywhere in the SGS and SO yielded dense label in almost all of the caudal (LPc) and rostrolateral (LPrl) subnuclei of LP, ipsilaterally, and sparser labeling in these same subnuclei, contralaterally. No injection produced significant labeling in the rostromedial (LPrm) subnucleus. Our autoradiographic data gave no indication of any topographic order in the tecto-LP projection. Electrophysiological methods were also used to map the tecto-LP projection. Multiple stimulating microelectrodes were positioned at physiologically defined sites in the SGS, and single cells were recorded in LP, ipsilaterally. Threshold currents for activation of LP cells from different collicular sites were then compared with the angular separation of SC and LP receptive-field centers. No significant correlation between these two variables was noted, again indicating a lack of topographic organization in the tecto-LP projection. The receptive-field properties of individual LP neurons (n = 211) were also assessed and correlated with subnuclear location and responsivity to SC shocks.(ABSTRACT TRUNCATED AT 400 WORDS)
Projections of hindlimb dorsal roots to lumbosacral spinal cord of cat
Authors: Culberson J. L. , Brown P. B.
Published: December 2017

Single dorsal roots of spinal nerves that contribute to the cat lumbosacral plexus (L3-S2) were cut to evoke degeneration of centrally projecting axons. Serial sections throughout lumbosacral cord levels were impregnated by the Fink-Heimer method (20) to permit charting of the distribution patterns of segmental dorsal root afferent fibers. Afferent fibers that enter a single dorsal root have an extensive distribution to multiple cord segments; their longitudinal extent varies with entry level and with laminar targets. Afferent projections to the ventral horn reach motor nuclei only in their entry segment and the adjacent segments just above and below their entry. Those afferent fibers projecting to intermediate gray (laminae VI and VII) have the most extensive spinal distribution of any types; they may, from a single dorsal root, reach as many as 13 or 14 cord segments. Dorsal horn projections of single roots are also longitudinally expansive. Small-diameter afferent fibers course rostrally and caudally in Lissauer's tract (LT) for up to 9-10 segments. They appear to terminate in at least laminae I and II in and near their entry segment; their endings are difficult to demonstrate at greater distances where they are probably less dense. Larger caliber axons entering the dorsal horn generate a somatotopically organized projection, especially to laminae III and IV. Collaterals of these fibers appear to course longitudinally within the gray matter and they distribute to as many as six to seven segments.
Recovery from effects of brief monocular deprivation in the kitten
Authors: Malach R. , Ebert R. , Van Sluyters R. C.
Published: December 2017

The potential for recovery from the cortical effects of monocular deprivation (MD) was studied in kittens that were briefly deprived and then exposed to various periods of normal binocular vision. In eight kittens, recordings from the hemisphere ipsilateral to the deprived eye revealed that at 4 wk of age, exposure to 12 h of MD (six 2-h sessions spread over 2 days) was sufficient to cause a massive shift in the ocular dominance of striate cortex neurons in favor of the nondeprived eye. Six of these MD kittens were allowed 3 wk of normal binocular vision and then recorded from a second time to assess the extent to which their cortex could recover from the effects of this brief period of deprivation. Data from these animals indicated that now approximately equal numbers of cortical neurons were dominated by each eye and that, while the overall level of binocularity was somewhat lower than that found in normally reared animals, the majority of cells had regained functional binocular connections. The possibility that cortical binocularity could recover even further was explored by allowing four of these six MD kittens to experience an additional 4 wk of binocular vision and then recording from them a third time. These final recordings indicated that following a total of 7 wk of binocular vision, the level of cortical binocularity was no different from that found in normally reared animals. Having demonstrated that normal binocular function can be restored to a cortex in which it had been severely disrupted, we next attempted to characterize the earliest stages of this recovery process by examining the pattern of cortical binocularity in 10 MD kittens that were allowed to experience either 6 or 12 h of binocular vision (given over 1 or 2 days, respectively). Our results indicate that, during the initial day of binocular vision, recovery seems to involve a noncompetitive expansion of functional cortical input from the deprived eye, which joins with input from the nondeprived eye in driving cortical neurons. The level of cortical binocularity continues to increase during the next day of binocular vision, but now there is also a small increase in the proportion of cells driven exclusively by the initially deprived eye--suggesting that there may be an additional competitive component to the early stages of recovery. The results of this study complement our previous report of complete recovery of binocularity following exposure to a brief period of optically induced strabismus.(ABSTRACT TRUNCATED AT 400 WORDS)
Analysis of intracellularly recorded phasic bursting by mammalian neuroendocrine cells
Authors: Andrew R. D. , Dudek F. E.
Published: December 2017

Phasic bursting by magnocellular neuroendocrine cells (MNCs) in the mammalian supraoptic and paraventricular nuclei (SON and PVN) consists of successive periods of action potentials and inactivity. It has previously been correlated with increased release of vasopressin from the neurohypophysis. In the present studies we investigated the neuronal mechanisms underlying this firing pattern. Using coronal slices of rat hypothalamus, we recorded intracellularly from neurons that are considered to be MNCs, based on several criteria. Eight of the 29 cells in this study displayed phasic burst patterns similar to those previously recorded extracellularly from MNCs in intact animals. Among the eight phasic cells, low levels of steady current injection could dramatically alter burst periodicity. Steady hyperpolarization revealed patterned synaptic input in only one case; in the remainder of the cells, nonsynaptic mechanisms appeared to account for periodic bursting. The phasic burst pattern usually appeared to be spike dependent, each burst arising from one or several depolarizing after-potentials (DAPs). Summed DAPs formed a plateau potential, which provided a depolarizing drive for further spiking. Spike frequency decreased late in the burst, and then the plateau potential terminated. During the quiescent period, burst excitability appeared to increase coincident with a small slow depolarization. Spikes and their summating DAPs could then initiate another burst. In several silent MNCs, a brief supra-threshold current pulse could initiate a prolonged afterdischarge, which had the properties of a phasic burst. Two MNCs that fired with a fast-continuous pattern were tested with brief hyperpolarizing current pulses; after each pulse, spike activity ceased and a plateau potential was revealed. Therefore, it appears that a maintained plateau potential (summed DAPs) can drive fast-continuous firing. In one case a periodic bombardment of excitatory postsynaptic potentials (EPSPs) generated a phasic firing pattern. The dependence of the burst characteristics on membrane potential, the apparent lack of patterned synaptic input in most cells, and the ability to evoke bursts with brief stimuli support the hypothesis that bursting in some MNCs involves an endogenous mechanism. Furthermore, phasic firing may be driven by tonic excitatory input. The data on phasic, silent, and fast-continuous cells suggest that many MNCs can generate DAPs and plateau potentials.
Spinal cord pathways involved in initiation of swimming in the stingray, Dasyatis sabina: spinal cord stimulation and lesions
Authors: Williams B. J. , Livingston C. A. , Leonard R. B.
Published: December 2017

In spinally transected stingrays, electrical stimulation of a site just ventral to the dorsal root entry zone or a site in the intermediate portions of the lateral funiculus produced rhythmic swimming like movements of the contralateral pectoral fin. Electromyographic (EMG) records collected during cord-stimulated rhythms had the same pattern of activity and sometimes the same intersegmental coordination as those collected during spontaneous swimming of the same animal. In paralyzed, high-spinal stingrays, the only stimulation sites that produced rhythmic activity (fictive swimming) in the pectoral fin motor nerves were in the intermediate portion of the lateral funiculus. The evoked rhythm occurred in the motor nerves that were contralateral to the stimulated side of the spinal cord. The effects of subtotal lesions of the rostral spinal cord on spontaneous swimming behavior were assessed by analysis of EMG records taken before and after the lesions were made. Severe deficits in swimming occurred after bilateral ablation of intermediate portions of the lateral funiculi. In agreement with previous results, the stimulation experiments indicate that the stingray spinal cord contains an inherent capacity to generate properly coordinated rhythmic swimming. The current experiments also suggest that the descending pathways(s) that normally functions to initiate swimming projects through the intermediate aspects of the lateral funiculi.
Quality coding of a complex odorant in an invertebrate
Authors: Derby C. D. , Ache B. W.
Published: December 2017

Mechanisms whereby the olfactory system of the spiny lobster codes food odors were quantitatively analyzed. A 23-component chemical mixture, with a composition based on a tissue extract from a known food of lobsters, and 8 of the mixture's components were used to describe responses of single cells at two neural levels: a) olfactory receptor cells and b) low-order interneurons projecting from the main olfactory center of the brain. Cluster analysis identified six classes of narrowly tuned receptor cells. Interneurons, on the other hand, were significantly more broadly tuned than receptor cells and could not be grouped into a small number of discrete, highly correlated cell types. Nonetheless, some chemosensory interneurons (unimodal interneurons) had specificities as narrow as receptor cells. Across-neuron correlations between stimuli showed that the increase in neuronal breadth of responsiveness from the level of receptors to the level of interneurons was paralleled by an increase in similarity in across-neuron patterns and, therefore, a decline in ability to discriminate between any two compounds. Across-neuron correlations between concentrations of a given compound showed that stimulus quality had a much stronger effect on across-neuron patterns than did stimulus quantity and, hence, stimulus qualities could be distinguished in spite of concurrent changes in stimulus quantity. Coding of odor quality could be accomplished at the receptor level by a labeled-lines code. At the interneuronal level, odor quality appears to be coded by across-fiber patterns. However, the finding that unimodal interneurons were as narrowly tuned as receptor cells indicates that specific channels for some food-odor components (e.g., taurine and glycine) are conserved even at higher neuronal levels. These narrow-spectrum interneurons may have a special function in quality coding either by dominating the interneuronal across-fiber pattern for that stimulus or by being processed independently of the broad-spectrum interneurons and thereby transferring information about certain components by way of specific channels to even higher neuronal levels.
Binaural interaction in low-frequency neurons in inferior colliculus of the cat. IV. Comparison of monaural and binaural response properties
Authors: Kuwada S. , Yin T. C. , Syka J. , Buunen T. J. , Wickesberg R. E.
Published: December 2017

We studied the monaural and binaural response properties of 82 low-frequency inferior colliculus (IC) neurons that display a clear sensitivity to changes in interaural phase. Most cells (60%) are excited by sound delivered to either ear, the remainder being excited only by stimulation of one ear; 70% of the neurons receive their stronger or sole excitatory input from the contralateral ear. A monotonic relation between spike discharge and sound pressure level (SPL) is seen in 65% of the monaural response areas, i.e., the range of stimulus frequencies and intensities effective in eliciting a response, while 30% show a nonmonotonic response pattern. In 33% of the cases there is a significant shift in the most effective frequency as a function of SPL. Most discharge patterns are classified as sustained (69%) and the remainder as onset. However, there is considerable variability within these patterns and often two types of discharges are present at different points in the same response area of a single cell. The sustained responses show a broad range of latencies, while onset patterns show a tighter distribution and shorter first spike latencies. Thus, IC neurons showing sensitivity to changes in interaural phase can differ in laterality preferences, response area characteristics, discharge patterns, and latency parameters. Given the diversity of inputs to the IC from lower brain stem structures, this heterogeneity is not surprising. For most neurons excited by stimulation to either ear, the characteristic frequencies, discharge patterns, and first spike latencies are similar, suggesting that the monaural inputs to a binaural cell are of the same type. A neuron's most effective frequencies at a particular SPL for monaural and binaural stimulation are, in general, the same. In some cases a neuron's monaural and binaural response areas can show remarkable similarities, suggesting that certain monaural features are intimately related to the binaural response. In 18% of the IC cells, phase locking to the monaural stimulating frequency is seen. When both inputs are phase locked, a simple coincidence model can predict the interaural phase or delay at which the maximal binaural discharge occurs.
Tactile sensory coding during development: signaling capacities of neurons in kitten dorsal column nuclei
Authors: Connor K. M. , Ferrington D. G. , Rowe M. J.
Published: December 2017

The functional maturation of cuneate neurons was studied using reproducible tactile stimulation procedures and quantitative assessment of coding capacities in anesthetized (N2O/O2 plus barbiturate infusion) or decerebrate cats from six different age groups; neonatal (1-5 days), 10-15, 25-30, 55-63, and 83-90 days, and an adult group. Cuneate neurons were distinguished from input fibers to the nucleus on criteria of spike configuration and time course and on response profiles. Extracellular spike durations underwent a progressive shortening with age, reaching the adult range at approximately 3 mo when background activity levels also reached maturity. Despite an increase in conduction-path length, response latencies decreased to adult values by 25-30 days of age, presumably reflecting the increased conduction velocity in the input fibers. In each age group three functional classes of neurons responsive to tactile stimulation of the footpads were identifiable. One consisted of slowly adapting neurons whose stimulus-response relations resembled those of the adult in responsiveness and dynamic range by 25-30 days postnatal age. The remaining neurons were purely dynamically sensitive, but among them two classes could be distinguished by their differential sensitivity to cutaneous vibration, one receiving rapidly adapting (RA) fiber input the other pacinian corpuscle (PC) input. The combined bandwidth of vibration sensitivity in dynamically sensitive cuneate neurons expands from approximately 5-300 Hz in the neonate to the mature range of 5-1,000 Hz by 1 mo of age. The PC class of cuneate neurons showed an upward shift in peak sensitivity from 30-200 Hz in the neonate to 100-300 Hz at 10-15 days, reaching adult values of 200-600 Hz by 25-30 days. Over this period absolute thresholds dropped by an order of magnitude at 200-500 Hz reflecting the threshold trends in primary PC fibers. During the first 1-2 postnatal months, the capacity of cuneate PC neurons to signal information in a pattern code about vibration frequencies around 300 Hz is restricted because of poor phase locking and low responsiveness, which preclude an impulse periodicity reflecting the vibratory frequency.(ABSTRACT TRUNCATED AT 400 WORDS)
Presynaptic membrane potential and transmitter release at the crayfish neuromuscular junction
Authors: Wojtowicz J. M. , Atwood H. L.
Published: December 2017

Release of transmitter was evoked at neuromuscular junctions of the crayfish opener muscle by passage of current through an intracellular electrode impaling a branch of the motor axon close to a muscle fiber. Membrane-potential changes in the presynaptic axon branch were monitored, together with postsynaptic potentials. Depolarization of impaled secondary axonal branches by more than 10 mV led to an increase in asynchronous transmitter release. The release was facilitated by prolonged (50-500 ms) depolarizations and it decayed rapidly when depolarization was terminated. Ca2+ was essential for facilitated release; however, no indication of a Ca spike was found at the recording site. Input-output curves for the synapse were obtained by applying depolarizing pulses of varying amplitude to the axon branch. Transmitter output was strongly influenced by both amplitude and duration of the applied depolarization. During normal synaptic transmission, propagated Na+-dependent action potentials were recorded in the secondary axonal branches but there was no evidence for a calcium-dependent component for these action potentials. Evoked release was dependent on Ca2+ and was steeply dependent on the amplitude of the action potential, which could be made variable in size by application of tetrodotoxin (TTX). Prolonged depolarization of axonal branches resulted in enhancement of transmitter release evoked by an action potential. The enhancement occurred in spite of a simultaneous reduction of the amplitude of the action potential. Morphological features of the terminals were investigated after injection of lucifer yellow into the axon. An electrical model incorporating the morphological features suggests that membrane-potential changes set up in the main axon reach the nearest terminals with 30-40% attenuation, while events originating in the terminals would be severely attenuated in the main axon. Comparison of the crayfish synapse with other frequently studied synapses shows both similarities and differences, suggesting that it is not possible to apply findings made in one synapse to all others.
Phasic and tonic modulation of impulse rates in gamma-motoneurons during locomotion in premammillary cats
Authors: Murphy P. R. , Stein R. B. , Taylor J.
Published: December 2017

To determine the role of gamma-motoneurons in the control of locomotion, we isolated single units from nerves to triceps surae muscles in the premammillary cat. The limb used for recording was largely denervated, except for the muscles of interest, and fixed in place, while the other three limbs walked on a treadmill. One type of gamma-motoneuron (13 units) had a high impulse rate at rest, which changed little on average during walking, but was deeply modulated with each step (phasically modulated gamma-motoneuron or gamma p). Another type (19 units) had a low impulse rate at rest, which increased greatly on average during walking, but was not highly modulated with each step (tonically modulated gamma-motoneuron or gamma t). Peak gamma p rates generally occurred after peak EMG, often near the peak of tension. In contrast, peak gamma t activity generally preceded peak electromyograms (EMG). No significant difference was observed in conduction velocities for the two types of units. At rest all gamma t units were excited by natural stimulation of the fur over a large part of the body surface, whereas 3 of 11 gamma p units were inhibited. During locomotion the same natural stimuli had no observable effect on either type of unit. By recording in continuity from fine branches of the lateral and medial gastrocnemius nerves and stimulating ventral root filaments in continuity, we identified dynamic and static gamma-motoneurons in terms of their effects on muscle spindle afferents. After cutting the nerve branch distally and other ventral root filaments supplying the muscle, the resting discharge of dynamic and static gamma-motoneurons was recorded and found to correspond to that of the gamma p and gamma t units, respectively. Other evidence is presented for a correspondence between phasically and tonically modulated units and dynamic and static gamma-motoneurons, contrary to some suggestions in the literature.
Repetitive firing in layer V neurons from cat neocortex in vitro
Authors: Stafstrom C. E. , Schwindt P. C. , Crill W. E.
Published: December 2017

Input-output relations of large neurons from layer V of cat sensorimotor cortex were studied in an in vitro slice preparation using steps and ramps of intracellularly injected current. Depolarization attained during the interspike interval (ISI) was compared to the voltage levels required to activate a previously described (29) persistent sodium current (INaP). INaP was studied using a single-electrode voltage clamp in the same cells tested for firing behavior. Following an injected current step, firing rate declined smoothly to a steady level with a time course that was approximately exponential in most cells (tau, 9-43 ms). In most cells, the relation between firing rate and injected current (f-I relation) consisted of two linear segments, both for adapted, steady firing and for early intervals during adaptation. The slope of the steeper, initial (or sole) linear segment of the f-I curve averaged 26.2 Hz/nA during steady firing and was steeper when plotted for early interspike intervals. The variation of the depolarization at which spike initiation occurred (firing level) and the membrane potential between rhythmic spikes was examined during adaptation and steady firing. In most cells, firing level rose rapidly during a rhythmic train to a steady value. The steady firing level attained remained unchanged over a wide range of steady firing rates. Nevertheless, the mean depolarization during the interspike interval (V) increased approximately linearly with steady firing rate. Even at the slowest firing rates, V is sufficient to activate INaP. The use of injected current ramps demonstrated that neocortical cells were sensitive to rate of change of stimulus current (dI/dt) as well as its amplitude (I). The use of ramps followed by steady currents demonstrated that the repetitive response lagged behind changes in stimulus parameters and did not reach a steady state even during slow ramps; i.e., the response depended on time as well as on I and dI/dt. Instantaneous firing rate during the ramp increased linearly with time for a wide range of ramp slopes (dI/dt). The instantaneous firing rate of early interspike intervals was also linearly related to ramp slope for small ramp slopes. In spite of these linear relationships, quantitative analysis indicated that firing rate during ramp stimulation cannot, in general, be described by a simple linear combination of separate amplitude- and rate-dependent terms. The repetitive firing properties of the in vitro neurons are compared to those of in vivo neocortical neurons and other cell types.(ABSTRACT TRUNCATED AT 400 WORDS)
Neural control of vergence eye movements: activity of abducens and oculomotor neurons
Authors: Mays L. E. , Porter J. D.
Published: December 2017

Single<unit recordings were made from neurons with horizontal eye position sensitivity in the oculomotor and abducens nuclei in alert monkeys. The animals were trained to perform a visual tracking task that resulted in conjugate eye movements or symmetrical vergence movements. Scatterplots were obtained for unit firing rate as a function of the position of the ipsilateral eye for both types of movement. The slopes of the linear regression line were computed for conjugate (kc) and vergence movements (kv). Previous recording studies implied that kv should be equal to kc for most, if not all, abducens and oculomotor neurons. Other lines of evidence suggested that kv should be zero for a substantial proportion of abducens neurons. In the abducens nucleus, we found some cells for which kv matched kc, and a few cells with a kv value of zero. However, the majority of abducens units had vergence signals that were neither equal to zero nor to their conjugate signals. Overall, kv/kc was 0.62, and the correlation between kv and kc was not significantly different from zero. Similarly, in the oculomotor nucleus, kv was significantly different from kc for a majority of the cells. A few units had kv values less than or equal to zero, whereas other cells had very high kv values. Overall, the kv/kc for oculomotor units was nearly unity (0.94), and the correlation between kv and kc was 0.31. These results confirm previous reports that most neurons in the abducens and oculomotor nuclei with a horizontal eye position sensitivity carry both conjugate and vergence eye movement signals. We do not find that the relative magnitudes of these signals are closely matched for most neurons. It is more likely that vergence and conjugate signals are matched globally, for an entire nucleus, rather than for individual motoneurons. This view is consistent with the hypothesis that conjugate and vergence signals are generated independently and combined for the first time at the motoneurons. Our results also imply that some motoneurons play a more important role than others in either vergence or conjugate movements.
Directional filter characteristics of optic nerve fibers in California ground squirrel (Spermophilus beecheyi)
Authors: McCourt M. E. , Jacobs G. H.
Published: December 2017

Directional units in the optic nerve of the California ground squirrel (Spermophilus beecheyi) were studied with respect to their response to diffuse light, preferred directions of motion, tuning for preferred direction, the relationship between spatial and directional tuning characteristics, and receptive-field size and areal summating properties. Directional units in the ground squirrel optic nerve are of the “on-off” type. No purely on or off units were encountered in a sample of 356 directionally selective fibers. The distribution of preferred directions of image motion for 356 units was significantly anisotropic; greater than 50% of the directional units prefer motion in the direction of the superior-nasal visual quadrant. Mean directional bandwidth, measured at half-amplitude response, for 39 units was 88.5 degrees. The distribution of directional bandwidths suggests that two subpopulations of directional units may exist a broadly tuned (106.4 degrees bandwidth) group preferring image motion in the superior-nasal direction, and a narrowly tuned group (59.9 degrees bandwidth) with a uniform distribution of preferred direction. Tuning for direction of motion and for spatial frequency were significantly positively correlated in a sample of 35 directional units. Area-vs.-response measures for directional units show that they possess excitatory discharge centers with a concentric antagonistic surround, plus a larger suppressive surround activated specifically by moving luminance contours, which may be asymmetric. Critical activation areas for directional units, as measured along orthogonal orientations, were highly positively correlated. This suggests that these receptive fields possess the property of linear spatial summation, not of luminance flux, but of areas of moving luminance contours.
Morphological correlates of physiologically identified Y-, X-, and W-cells in cat retina
Authors: Fukuda Y. , Hsiao C. F. , Watanabe M. , Ito H.
Published: December 2017

The action spike activities of single ganglion cells were recorded from the nasal retina of the intact eye of anesthetized and immobilized cats. Each ganglion cell was identified as a Y-, X-, or W-cell on the basis of its axonal conduction velocity, its receptive-field properties, and the level of maintained activity. Of about 100 ganglion cells physiologically identified and penetrated with horseradish peroxidase (HRP)-containing glass microelectrodes, 21 cells were subsequently identified in flat-mount preparations of the retinas and processed for detection of HRP. Of a total of nine Y-cells recovered, four had been penetrated at the soma and five at the axon. All had the morphology of the alpha-cell of Boycott and Wassle. Eight X-cells recovered. All had been penetrated at the soma and showed beta-cell morphology. Four W-cells were penetrated at the soma and recovered. Two off-tonic W-cells had small somas (15-16 micron in diam) and sparse dendritic fields, resembling gamma-cells of Boycott and Wassle. They are also similar to “G4” and “G18” of Kolb et al.'s classification. One on-tonic W-cell had somewhat larger soma (18 micron) with a relatively densely branched dendritic field. This corresponds to delta-cell of Boycott and Wassle or to “G15” of Kolb et al. One on-off phasic W-cell had a medium-sized soma (25.3 micron) with a fanlike dendritic expansion characteristic of the “unilateral horizontal broad range cell” of Shkolnik-Yarros or of “G22” of Kolb et al. Alternatively, all these W-cells can be called medium-sized gamma-cells. Among all three classes of ganglion cells, a positive correlation was found between the diameter of the receptive-field center and the dendritic field. Assuming that in the cat retina 1 degree of visual angle = 230 micron, dendritic fields of Y-cells seemed larger than their physiologically determined receptive-field centers. By contrast, the reverse relation was found between these two dimensions in X-cells. Axon diameters ranged from 4.0 to 5.6 micron (mean, 4.5 micron) in Y-cells and from 1.9 to 2.7 micron (mean, 2.2 micron) in X-cells. Three W-cells showed axon diameters of 0.6, 1.1, and 1.8 micron. The axon diameter distributions made from axons labeled by massive injections of HRP into the optic nerve fiber layer showed a pattern of distribution similar to that obtained from physiologically identified Y-, X-, and W-cell axons.
Contrasting neuronal activity in supplementary and precentral motor cortex of monkeys. II. Responses to movement triggering vs. nontriggering sensory signals
Authors: Kurata K. , Tanji J.
Published: December 2017

This report compares neuronal activity in the supplementary motor area (SMA) and the precentral motor cortex (PCM) in response to auditory and vibrotactile signals that required a monkey either to start a key-press movement or to refrain from initiating such a movement. Confirming previous reports (3, 9), a vibrotactile stimulus that triggered movement gave rise to two phases of neuronal activity in PCM neurons: a short-latency response time-locked to the occurrence of the vibrotactile stimulus, and a response related to the time of onset of the movement. When the animal was required to refrain from moving in response to the vibrotactile signal, the short-latency response was often attenuated and there was rarely any later activity. There was no attenuation of the short-latency response to the nontriggering vibrotactile stimulus in the anterior part of the postcentral somatosensory cortex. As reported previously (23), short-latency stimulus-locked responses of SMA neurons to a vibrotactile signals were less frequent and the magnitude of the responses was smaller than in the PCM. However, the properties of the later-occurring responses of SMA neurons were often different from those of PCM neurons. Many SMA neurons responded to both the triggering and nontriggering vibrotactile signals. Twenty-nine SMA neurons responded to the nontriggering signal only and not to the movement-triggering signal. Most of the PCM neurons were active after the auditory signal only when the signal was a trigger to start the key-press movement; three neurons exhibited a slight activity increase after the nontriggering auditory signal. In contrast, a number of SMA neurons responded to the nontriggering auditory signal as well as the movement-triggering auditory signal. Twenty-three neurons responded exclusively to the nontriggering auditory signal. These results indicate the extent to which SMA neuronal activity, in contrast to that of the PCM, is related to factors other than the execution of movement.
Projection from dorsal column nuclei to dorsal mesencephalon
Authors: Cooper L. L. , Dostrovsky J. O.
Published: December 2017

This study investigated the projection from the dorsal column nuclei (DCN) to the dorsal mesencephalon. Single-unit extracellular recordings were obtained from the DCN of alpha-chloralose anesthetized cats. Neurons were identified by standard antidromic stimulation criteria as projecting to the dorsal mesencephalon (M neurons), the diencephalon (D neurons), or to both regions (MD neurons). Fifty-two neurons could be antidromically activated from the dorsal mesencephalon. Of these, 31 could also be antidromically activated by stimulation in the diencephalon. An additional 34 neurons were studied that could be antidromically activated only from the diencephalon. Stimulation sites within the dorsal mesencephalon effective in antidromically activating M and MD neurons were in the caudal ventrolateral superior colliculus, the intercollicular area, and external nucleus of the inferior colliculus. Effective diencephalic stimulation sites were in the ventroposterolateral nucleus, the zona incerta, and the magnocellular division of the medial geniculate. The antidromic latencies to stimulation in the dorsal mesencephalon of M and MD neurons spanned a similar but wide range of values in contrast to the latencies to stimulation in the diencephalon of D neurons which were all short. Conduction velocities along the mesencephalic and diencephalic collaterals of MD neurons were similar. Many of the neurons projecting to the mesencephalon had receptive fields located proximally on the body. Most of the neurons had rapidly adapting responses to low-intensity mechanical stimulation of the skin. The major difference between the mesencephalic M and MD projection neurons and diencephalic projection D neurons was the larger percentage of neurons having proximal receptive fields in the former group. These findings are the first electrophysiological demonstration of a direct somatosensory input to the dorsal mesencephalon arising in the DCN. This input is probably responsible for providing some of the somatosensory input to the deeper layers of the superior colliculus, the external nucleus of the inferior colliculus, and the intercollicular area, regions known to have neurons responding to somatosensory stimuli.