bluuebunny/crossref_metadata_2025 huggingface dataset:
Scotopic threshold response of proximal retina in cat
Authors: Sieving P. A. , Frishman L. J. , Steinberg R. H.
Published: December 2017

We describe a new response in proximal retina of cat that is present under scotopic conditions, clearly differs from PII (b-wave and DC component) and contributes a negative potential at threshold to the diffuse electroretinogram (ERG). We have termed this response the scotopic threshold response (STR). Extracellular potentials evoked in response to circular spots of light at dark-adapted threshold, and with dim backgrounds, were recorded with microelectrodes placed intraretinally at different depths. The dark-adapted response of proximal retina (STR) consisted of a graded negative potential to the onset of illumination that maintained amplitude during illumination and decayed back toward the base line at stimulus offset without evidence of a negative-going off response. It thereby differed in form from the photopic M-wave response of proximal retina, which has a negative-going off response. It also did not exhibit spatial tuning, simply increasing in size with stimulus area. In addition, the STR appears to be a rod-driven response whose threshold approximates that of the most sensitive ganglion cells in cat, whereas the M-wave is a much higher threshold cone-driven response. The STR could be clearly distinguished from PII on the basis of its form, depth-distribution, and dynamic range. For example, the STR had its maximum amplitude in the proximal retina at 17% retinal depth, whereas scotopic PII had its maximum in the distal retina at 48% retinal depth. Also, the STR had a lower threshold than PII intraretinally and saturated well below the level of saturation of scotopic PII (rod saturation). By analogy to the PNR and M-wave, the STR is hypothesized to represent either an extracellular voltage arising from proximal retinal neurons or Muller cell responses to K+ released by these neurons. Recording in the vitreous, near the retinal surface, showed that the STR always had a negative polarity. The polarity reversal of the STR at 50-60% retinal depth (from negative, proximal to positive, distal) suggested the presence of a sink proximal to the reversal point and a source distal to it. We also recorded the vitreal ERG in response to diffuse illumination of the dark-adapted retina. The STR could be clearly identified in the scotopic ERG as a threshold negative potential that had been observed previously in the mammalian ERG. The STR differs, therefore, from PII (b-wave and DC component) that is a higher threshold positive component in the diffuse ERG.(ABSTRACT TRUNCATED AT 400 WORDS)
Unit study of monkey frontal cortex: active localization of auditory and of visual stimuli
Authors: Vaadia E. , Benson D. A. , Hienz R. D. , Goldstein M. H.
Published: December 2017

The influence of sound localization behavior on unit activity in the frontal cortex of awake rhesus monkeys was examined by comparing responses under three behavioral conditions: auditory localization, during which a response was required to the location of a sound (broad-band noise) source; auditory detect, during which a response was required to indicate the occurrence of the sound regardless of location; visual localization, during which no sounds were presented and a response was required to the location of a visual stimulus; and nonperform, presentation of auditory stimuli as in the first two conditions, but with the animal sitting passively. Extracellular microelectrode recordings were made in the periarcuate region and dorsal and ventral prefrontal areas near the principal sulcus. Four monkeys were used with a total of 498 cells studied. Of the total population, only five cells were found to have characteristics similar to those of auditory units in the primary auditory cortex and the surrounding belt area. More typically, units were found that had strong short-latency responses specific to the auditory and/or visual localization tasks. These units had no or weak responses when the same sound stimuli were presented in the auditory detect task or when a monkey received the sound stimuli in a nonperforming condition. Two regions were identified, one medial and/or posterior to the arcuate sulcus, in Brodmann's area 6; the second included parts of areas 8 and 9 within the genu of the arcuate sulcus. Units from these regions are referred to, respectively, as the postarcuate and the prearcuate populations. Both populations responded predominantly during active localization behavior. Sixty-two percent of the postarcuate population responded during auditory localization, 32% responded during auditory detect, and only 18% responded to acoustic stimuli presented in the nonperforming condition. In the prearcuate population percentages in these three conditions were 35, 25, and 12%, respectively. For visual localization, 54% in the postarcuate population responded, whereas 42% in the prearcuate responded. Spatial tuning of units during auditory localization was similar to that seen in units of the primary auditory cortex, with the greatest percentages of units responding to stimuli contralateral to the recording site. Similar tuning was observed for the visual localization task as well. Similarities in spatial tuning between the auditory and visual localization conditions were examined to assess the "bimodal" nature of the units.(ABSTRACT TRUNCATED AT 400 WORDS)
Characteristics of synergic relations during isometric contractions of human elbow muscles
Authors: Buchanan T. S. , Almdale D. P. , Lewis J. L. , Rymer W. Z.
Published: December 2017

We studied the patterns of EMG activity in elbow muscles in three normal human subjects. The myoelectrical activity of 7-10 muscles that act across the human elbow joint was simultaneously recorded with intramuscular electrodes during isometric joint torques exerted over a range of directions. These directions included flexion, extension, varus (internal humeral rotation), valgus (external humeral rotation), and several intermediate directions. The forces developed at the wrist covered a range of 360 degrees, all orthogonal to the long axis of the forearm. The levels of EMG activity were observed to increase with increasing joint torque in an approximately linear manner. All muscles were active for ranges less than 360 degrees and most were active for less than 180 degrees. The EMG activity was observed to vary in a systematic manner with changes in torque direction and, when examined over the full angular range at a variety of torque levels, is simply scaled with increasing torque magnitude. There were no torque directions or torque magnitudes for which a single muscle was observed to be active alone. In all cases, joint torque appeared to be produced by a combination of muscles. The direction for which the EMG of a muscle reached a maximum value was observed to correspond to the direction of greatest mechanical advantage as predicted by a simple mechanical model of the elbow and relevant muscles. Muscles were relatively inactive during varus torques. This implies that the muscles were not acting to stabilize the joint in this direction and could have been allowing ligaments to carry the load. Plots of EMG activity in one muscle against EMG activity in another demonstrate some instances of pure synergies, but patterns of coactivation for most muscles are more complicated and vary with torque direction. The complexity of these patterns raises the possibility that synergies are determined by the task and may have no independent existence. Activity in two heads of triceps brachii (medial head--a single-joint muscle and long head--a two-joint muscle) covaried closely for a range of torque magnitudes and directions, though shoulder torque and hence the forces experienced by the long head of the triceps undoubtedly varied. The similarity of activation patterns indicates that elbow torque was the principal determining factor. The origins of muscle synergies are discussed. It is suggested that they are best understood on the basis of a model which encodes limb torque in premotor neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Short-latency ocular following responses of monkey. I. Dependence on temporospatial properties of visual input
Authors: Miles F. A. , Kawano K. , Optican L. M.
Published: December 2017

The ocular following responses elicited by brief unexpected movements of the visual scene were studied in 10 rhesus monkeys. Test patterns were either random dots or sine-wave gratings [spatial frequency (Fs) 0.046-1.06 cycles per degree (c/degree)]. Test stimuli were velocity steps [speed (V) 5-400 degrees/s] of 100-ms duration, applied 50 ms after spontaneous saccades to avoid saccadic intrusions. Eye velocity response profiles were nonmonotonic and idiosyncratic, but consistent and closely time-locked to stimulus onset. Two measures of response amplitude were used: initial peak in eye velocity (ei), and average final eye velocity over the period of 110-140 ms measured from stimulus onset (ef). Using random dot patterns, response latencies were short, e.g., when the criterion for onset was an eye acceleration of 100 degrees/s2, mean latency (+/- SE) for eight monkeys with a 40 degrees/s test ramp was 51.5 +/- 0.6 ms. Using gratings of low spatial frequency (Fs less than 0.5 c/degree), latency was inversely related to, and solely a function of, contrast and temporal frequency, Ft (where Ft = V X Fs). We conclude from the latter that ocular following is triggered by local changes in luminance, and propose a model of the detection mechanism that reproduces all the essential features of these data. Moderate low-pass spatial filtering ("blurring") of the random dot pattern, by interposing a sheet of ground glass between the animal and the scene, progressively increased the response latency and decreased ef, but ei was either little affected or increased. When used with gratings, the ground glass simply reduced the contrast (range: 0.5-0.003), with very similar consequences for ocular following: latency increased and ef decreased, but ei changed little over the first decade of contrast reduction, increased over the second, and began to show attenuation (often pronounced) only at the lowest contrast. We suggest that these anomalous increases in ei with reductions in contrast are secondary to the delay in response onset and might be explained if the motion detectors responsible for triggering ocular following act as a gate for integrated retinal slip inputs to the tracking system proper: the delay in detection causes a buildup in the error signal driving the tracking response. En masse movement of the visual field was not the optimal stimulus for ocular following.(ABSTRACT TRUNCATED AT 400 WORDS)
Responses of midbrain dopamine neurons to behavioral trigger stimuli in the monkey
Authors: Schultz W.
Published: December 2017

Destruction of the midbrain dopamine (DA) system in Parkinsonian man and experimental animals leads to deficits in initiation of behavior, motor performance, and cognitive mechanisms. We have investigated the extracellular impulse activity of single midbrain DA neurons in unlesioned monkeys performing in a controlled behavioral task that was designed to paradigmatically test behavioral reactivity. Animals were trained to execute natural forelimb reaching movements for food reward in response to a trigger stimulus. Presumptive DA neurons were histologically located in the pars compacta of substantia nigra and in neighboring areas A8 and A10. They spontaneously discharged polyphasic impulses of relatively long duration (1.4-3.6 ms) and at low frequencies (0.5-8.5/s). Systemic injections of low doses of the DA autoreceptor agonist apomorphine (0.05-0.2 mg/kg) depressed the activity of virtually all thus tested DA neurons. In following established criteria, these characteristics strongly suggest the DAergic nature of the recorded neurons. The majority of midbrain DA neurons (70 of 128) responded to the behavioral trigger stimulus of the task with a short burst of impulses. Latencies ranged from 39 to 105 ms (median 65 ms) for onset and from 65 to 165 ms (median 95 ms) for peak of responses. Responses occurred before arm movement and at the time of or before onset of electromyographic (EMG) activity in prime mover muscles. Responses were time-locked to the stimulus and not to the onset of movement or EMG. Responses remained present in most neurons but were reduced when vision of the behavioral trigger stimulus was prevented while maintaining the associated acoustic signals. In another variation of the task, most neurons also responded to a stimulus that was physically identical to the behavioral trigger but to which the animal made no movement. The activity of a few DA neurons (11 of 128) was reduced following presentation of the behavioral trigger stimulus, with latencies comparable to those of activations. The activity of many DA neurons was increased (40 of 128) or reduced (22 of 128) during execution of the forelimb reaching movement. These changes were of a slow and moderate nature, and were minor compared with responses to the behavioral trigger stimulus. About half of movement-related neurons also responded to the behavioral trigger. The activity of a few DA neurons was increased (11 to 128) or reduced (1 to 128) when the food reward reached the mouth. These changes did not occur with spontaneous mouth movements. About half of these neurons also responded to the behavioral trigger.(ABSTRACT TRUNCATED AT 400 WORDS)
A thalamic terminus of the lateral cervical nucleus: the lateral division of the posterior nuclear group
Authors: Metherate R. S. , da Costa D. C. , Herron P. , Dykes R. W.
Published: December 2017

The submodality and receptive field properties of single units in the lateral cervical nucleus (LCN) of barbiturate anesthetized cats were studied with glass microelectrodes. In other experiments, a region of the posterior thalamus containing neurons with properties comparable to those seen in the LCN was examined with tungsten microelectrodes. The responses of most units in the LCN reflected a major input from large myelinated afferent fibers innervating guard hairs but no input from Pacinian afferent fibers. The large size of the receptive fields indicated that excitatory input converged selectively from afferent fibers serving hairs over large areas of the body. In the posterior thalamus rapidly adapting neurons characterized by very large receptive fields and driven by the movement of guard hairs were observed to a region identified histologically as the rostral extension of the lateral division of the posterior nuclear group (POl). Caudally this region was located immediately adjacent to the dorsolateral part of the ventroposterior inferior nucleus (VPI). In more rostral parts of the thalamus it was located more dorsally and the ventroposterior lateral nucleus intervened between it and the VPI. This region was less than 1 mm wide in the frontal plane but extended rostrocaudally for several millimeters. Horseradish peroxidase injected into the region of the VPI and the POl labeled many cells in the LCN and the caudal pole of the dorsal column nuclei demonstrating that neurons in the LCN relay information to this part of the thalamus. These data, plus previous experiments showing that the VPI receives a major projection from the caudal poles of the dorsal column nuclei, suggest that the rostral portion of the POl receives an important afferent supply from the LCN. The responses of neurons in the POl appear to arise from specific classes of sensory receptors and cannot be considered less precise or more primitive than responses observed in the ventroposterior nucleus of the thalamus.
A TTX-resistant propagating calcium action potential
Authors: Stockbridge L. L. , Ross W. N.
Published: December 2017

The cross-commissural (CC) cell in the supraesophageal ganglion of the giant barnacle, Balanus nubilus, was stimulated intrasomatically and antidromically in normal saline and 3 X 10(-7) M tetrodotoxin (TTX) saline. The action potential in normal saline contained both sodium and calcium components, each independently capable of propagation. Evidence that the action potential in TTX saline was calcium dependent included: the amplitude of the spike in TTX saline increased monotonically with increasing calcium; it was blocked by the calcium channel blockers La, Ni, Cd and Co; and equimolar substitution of Ba or Sr for Ca in TTX saline supported regenerative activity. Evidence that the calcium component could propagate alone included: the distance over which the calcium action potential traveled exceeded the space constant of the axon; the biphasic nature of the extracellularly recorded action potential, which propagated to the axon in the nerve root, indicated inward regenerative current was occurring on the axon; electrotonically spread potentials were clearly distinguishable from active regenerative potentials. In addition, optical experiments using the calcium indicator dye arsenazo III (28) showed that the relative magnitude of the calcium signal was not diminished along the axon in TTX saline compared with normal saline. The critical external calcium concentration necessary to support the propagating action potential in TTX saline was estimated to be between 1.25 and 5 mM. To our knowledge, this is the first direct observation of a neuron with sodium and calcium channels of apparently normal kinetics where the calcium component alone can propagate in the absence of an outward current blocker. Our results suggest that there is a greater density of calcium channels on the CC axon than on the axons of other neurons.
The NMDA receptor antagonist 2-amino-5-phosphonovalerate blocks stimulus train-induced epileptogenesis but not epileptiform bursting in the rat hippocampal slice
Authors: Anderson W. W. , Swartzwelder H. S. , Wilson W. A.
Published: December 2017

The role of N-methyl-D-aspartate (NMDA) receptors in producing stimulus train-induced bursting (STIB) was examined in area CA3 of the rat hippocampus. Extracellular recordings were made from the CA3 pyramidal cell layer. Bursting was induced by trains of electrical stimuli delivered to the stratum radiatum of CA3, or by bath application of NMDA. The specific NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (APV) was then bath applied to test its ability to block STIB and NMDA activated bursting. A dose-response relation for NMDA activation indicated that bath application of 1 and 5 microM NMDA had little or no effect on the response to a paired stimulus pulse (triggered response) and did not induce spontaneous bursting. Ten micromolar NMDA induced strong triggered and spontaneous bursting during the application of NMDA in 72% of the slices. Fifty to one hundred micromolar NMDA caused the abolition of the excitatory postsynaptic potential (EPSP) and orthodromic population spike and the decrease or abolition of the antidromic population spike. In the normal medium wash following 10 microM NMDA, those slices that produced triggered and spontaneous bursting in 10 microM NMDA underwent an early phase of decreased excitability in which spontaneous bursting occurred in only 6% of the slices that were bursting in NMDA. Later in the wash spontaneous bursting began occurring in half of the slices that were bursting in NMDA, and the excitability of the triggered bursts increased slightly. The ability of the NMDA receptor antagonist APV to block NMDA-activated bursting was tested. Bath application of 100 or 200 microM APV alone caused little change in the normal triggered response. When 10 microM NMDA was added to the APV solution, there was little or no change in the triggered response, and no spontaneous bursting occurred. However, when 100 or 500 APV was added to the NMDA solution after NMDA burst activation had occurred, triggered bursting was reduced, but not blocked, although spontaneous bursting was blocked. In those slices that continued bursting after the washout of NMDA, bath application of 100 or 500 microM APV reduced, but did not block, triggered bursting. Spontaneous bursting continued in all slices. The ability of APV to block the induction of bursting by trains of electrical stimuli was then tested.(ABSTRACT TRUNCATED AT 400 WORDS)
Temporal encoding of two-dimensional patterns by single units in primate inferior temporal cortex. III. Information theoretic analysis
Authors: Optican L. M. , Richmond B. J.
Published: December 2017

Ablation and single-unit studies in primates have shown that inferior temporal (IT) cortex is important for pattern discrimination. The first paper in this series suggested that single units in IT cortex of alert monkeys respond to a set of two-dimensional patterns with complex temporal modulation of their spike trains. The second paper quantified the waveform of the modulated responses of IT neurons with principal components and demonstrated that the coefficients of two to four of the principal components were stimulus dependent. Although the coefficients of the principal components are uncorrelated, it is possible that they are not statistically independent. That is, several coefficients could be determined by the same feature of the stimulus, and thus could be conveying the same information. The final part of this study examined this issue by comparing the amount of information about the stimulus that can be conveyed by two codes: a temporal waveform code derived from the coefficients of the first three principal components and a mean rate code derived from the spike count. We considered the neuron to be an information channel conveying messages about stimulus parameters. Previous applications of information theory to neurophysiology have dealt either with the theoretical capacity of neuronal channels or the temporal distribution of information within the spike train. This previous work usually used a general binary code to represent the spike train of a neuron's response. Such a general approach yields no indication of the nature of the neuron's intrinsic coding scheme because it depends only on the timing of spikes in the response. In particular, it is independent of any statistical properties of the responses. Our approach uses the principal components of the response waveform to derive a code for representing information about the stimuli. We regard this code as an indication of the neuron's intrinsic coding scheme, because it is based on the statistical properties of the neuronal responses. We measured how much information about the stimulus was present in the neuron's responses. This transmitted information was calculated for codes based on either the spike count or on the first three principal components of the response waveform. The information transmitted by each of the first three principal components was largely independent of that transmitted by the others. It was found that the average amount of information transmitted by the principal components was about twice as large as that transmitted by the spike count.(ABSTRACT TRUNCATED AT 400 WORDS)
Responses of nigrostriatal dopamine neurons to high-intensity somatosensory stimulation in the anesthetized monkey
Authors: Schultz W. , Romo R.
Published: December 2017

Nigrostriatal dopamine (DA) neurons of the mammalian midbrain play an important role in behavioral reactions. Their destruction in Parkinsonian patients and experimentally lesioned animals leads to a reduction and slowing of movements as well as other motor, cognitive, and motivational deficits. We tested the responses of DA neurons to somatosensory stimulation to gain insight into the nature of peripheral information reaching these neurons. Experiments were performed as repeated sessions in two anesthetized monkeys having chronically implanted recording chambers, thereby reducing the number of primates required for experimentation. Midbrain DA neurons were characterized by their histological location, by the form, duration, and frequency of extracellularly recorded, spontaneously occurring impulses, by antidromic activation from caudate and putamen, and by the reduction of impulse rate following systemic administration of low doses of the DA autoreceptor agonist apomorphine. Half of the midbrain DA neurons (65 of 145 neurons, 45%) were antidromically activated from chronically implanted stimulating electrodes in caudate (35 neurons), putamen (47 neurons), or both structures (17 of them). Conduction velocities ranged from 0.7 to 2.5 m/s, with medians of 1.2 and 1.5 m/s for neurons projecting to caudate and putamen, respectively. Half of the midbrain DA neurons were depressed (72 of 140 neurons, 51%) and less than a quarter activated (24 of 140 neurons, 17%) by intense noxious pinch stimulation to the body surface. Innocuous, even intense, surface or deep somatosensory stimuli were ineffective. Pinch responses continued during the whole stimulating period of several seconds in most DA neurons. There was no response habituation during repeated stimulation. Convergence between spinal and trigeminal input and from both body sides was seen for virtually all noxious pinch responses. Thus DA neurons typically responded in the same direction to pinch stimulation of hand, foot, face, tail, and dorsum of both sides. Systemic administration of the DA receptor antagonist haloperidol (0.33 or 0.50 mg/kg) strongly reduced pinch responses in all seven DA neurons tested. This provides evidence for an involvement of DAergic neurotransmission in the representation of exteroceptive input in the brain. The results show that midbrain DA neurons projecting to the striatum respond to noxious somatosensory input in the anesthetized monkey. The bilateral nontopographic nature of the responses does not support a role in precise stimulus recognition, rather it suggests a mechanism involved in basic neuronal processes underlying behavioral responsiveness.
The deafferented reticular thalamic nucleus generates spindle rhythmicity
Authors: Steriade M. , Domich L. , Oakson G. , Deschenes M.
Published: December 2017

The hypothesis that nucleus reticularis thalami (RE) is the generator of spindle rhythmicity during electroencephalogram (EEG) synchronization was tested in acutely prepared cats. Unit discharges and focal waves were extracellularly recorded in the rostral pole of RE nucleus, which was completely disconnected by transections from all other thalamic nuclei. In some experiments, additional transections through corona radiata created a triangular island in which the rostral RE pole survived with the caudate nucleus, putamen, basal forebrain nuclei, prepyriform area, and the adjacent cortex. Similar results were obtained in two types of experiments: brain stem-transected preparations that exhibited spontaneous spindle sequences, and animals under ketamine anesthesia in which transient spindling was repeatedly precipitated during recording by very low doses of a short-acting barbiturate. Both spindle-related rhythms (7- to 16-Hz waves grouped in sequences that recur with a rhythm of 0.1–0.3 Hz) are seen in focal recordings of the deafferented RE nucleus. The presence of spindling rhythmicity in the disconnected RE nucleus contrasts with total absence of spindles in cortical EEG leads and in thalamic recordings behind the transection. Oscillations within the same frequency range as that of spontaneous spindles can be evoked in the deafferented RE nucleus by subcortical white matter stimulation. In deafferented RE cells, the burst structure consists of an initially biphasic acceleration-deceleration pattern, eventually leading to a long-lasting tonic tail. Quantitative group data show that the burst parameters of disconnected RE cells are very similar to those of RE neurons with intact connections. In the deafferented RE nucleus, spike bursts of RE neurons recur periodically (0.1–0.3 Hz) in close time-relation with simultaneously recorded focal spindle sequences. The burst occurrence of deafferented RE cells is greatly reduced after systemic administration of bicuculline. The preservation of both spindle-related rhythms in the disconnected RE nucleus, together with our recent experiments showing abolition of spindle oscillations in thalamic nuclei after lesions of RE nucleus (24), demonstrate that RE nucleus is the generator of spindle rhythms.
Physiological study of neurons in the dorsal and posteroventral cochlear nucleus of the unanesthetized cat
Authors: Rhode W. S. , Kettner R. E.
Published: December 2017

The responses of neurons in the posteroventral (PVCN) and dorsal (DCN) cochlear nucleus of the unanesthetized cat were determined for both long and short tones. These results were compared with recent studies in the barbiturate-anesthetized cat conducted in the same laboratory using similar stimuli and analysis programs. Every response pattern (poststimulus time histogram to short tones), which has been observed in previous studies using anesthetized animals, was also observed without anesthetic. The converse was also true: no novel response patterns were observed in the unanesthetized cat. This was also true for interval histogram, response area, isorate curve, and frequency sweep data. Some neurons were difficult to classify into existing descriptions of cochlear nucleus response patterns. For example: primary-like, onset, pauser, and buildup response patterns could also show chopper-like properties; onset-inhibitory, pauser, and buildup neurons appeared to form a response continuum rather than exist as separate response categories; and onset neurons with low characteristic frequencies (CFs) often showed sustained and strongly phase-locked responses below approximately 1,000 Hz. In addition, single neurons often showed more than one response pattern depending on the intensity and frequency of the acoustic stimulus. These ambiguities were also observed under anesthetic. Onset neurons within the PVCN appear to be well suited for the encoding of temporal and intensity information. At low stimulus frequencies they often respond to every cycle of a pure tone stimulus and exhibit the highest degree of phase-locking in the cochlear nucleus. The dynamic ranges associated with many onset neurons can exceed 80 dB compared with the 30- to 40-dB dynamic ranges associated with most other cochlear nucleus neurons. Onset neurons show a similar range of activities in the anesthetized cat. Neurons in the DCN have response properties that are more complex than those seen in the PVCN. Response patterns can change from sustained excitation to complete inhibition and are more often nonmonotonic near CF. DCN neurons can show well-defined tuning in the frequency domain and may be used to encode spectral information, but appear to be poorly suited for encoding temporal or intensity information as they are weakly phase-locked and have relatively small dynamic ranges. When DCN neurons "chop" they usually do so more slowly than do PVCN neurons. DCN neurons recorded in the anesthetized cat behave similarly. The relative frequency of a particular response pattern did vary with anesthetic state.(ABSTRACT TRUNCATED AT 400 WORDS)
Excitatory amino acid receptors of rod- and cone-driven horizontal cells in the rabbit retina
Authors: Massey S. C. , Miller R. F.
Published: December 2017

Intracellular recordings were obtained from horizontal cells in the superfused retina-eyecup preparation of the rabbit. Rod- and cone-dominated horizontal cells were studied using bath-applied excitatory amino acid analogues. Cone-dominated horizontal cell somas were depolarized by kainate (KA) or quisqualate (QQ) and their light responses were reduced or abolished. They were not affected by N-methyl-DL-aspartate (NMDLA) at concentrations up to 2 mM or by 2-amino-4-phosphonobutyrate (APB), a selective agonist for the ON bipolar cell. When synaptic transmission was blocked with cobalt, horizontal cell somas were hyperpolarized. Under these conditions, KA and QQ caused large depolarizations suggesting that these agents have a direct action on horizontal cell somas. Excitatory amino acid antagonists such as cis-2,3-piperidine dicarboxylic acid (PDA) and kynurenic acid (Kyn) hyperpolarized horizontal cell somas to the level of the light-driven membrane potential. These antagonists blocked both the light-driven responses and the depolarizing action of KA. The specific NMDA antagonist 2-amino-7-phosphonoheptanoate (AP-7) had no effect on the membrane potential or light-driven responses of horizontal cell somas. In contrast to a previous report, we found no evidence that low concentrations of NMDLA could hyperpolarize horizontal cells or act as a KA antagonist in the rabbit retina. Rod-dominated axon terminals were identified by waveform, threshold, and the presence of a large rod after-potential evoked by high light intensity. These cells were depolarized by KA and their light responses were attenuated. NMDLA and APB had no effect on these cells. The general antagonists, PDA and Kyn, hyperpolarized axon terminals and blocked their light-evoked responses. The specific NMDA antagonist, AP-7, had no effect on these cells. These results suggest that the synaptic receptors that mediate light input to both rod- and cone-dominated horizontal cells are kainate or quisqualate receptors. This implies that the rod and cone transmitters of the rabbit retina are similar, with the characteristics of an excitatory amino acid, such as glutamate.
Response properties of polymodal receptors studied using in vitro testis superior spermatic nerve preparations of dogs
Authors: Kumazawa T. , Mizumura K. , Sato J.
Published: December 2017

Characteristics of the polymodal receptor were studied using in vitro testis superior spermatic nerve preparations excised from anesthetized dogs. They were in most aspects similar to those reported previously using in vivo preparations. The majority (90%) of the tested polymodal units had small myelinated nerve fibers; the rest had nonmyelinated fibers. The mean mechanical threshold as determined by von Frey hairs was 17.5 g/mm2 (n = 476). There was a tendency for a unit with a higher conduction velocity to have a lower mechanical threshold. Bradykinin and hypertonic saline consistently caused a dose-dependent increase in discharge rate of these units; high K+ solution was also found to be a consistent stimulant. The responses of C-fiber receptors were not significantly different from those of A-delta-fibers. Heat stimulation up to 50 degrees C evoked discharges in 99 out of the total 103 units tested. The mean threshold temperature was 44.4 degrees C for the first trial. In 19 units in which the same heat stimulation was tested after an interval of 10 min, 10 units showed sensitization; 3 units were deactivated; and no clear difference was observed in the rest. No unit responded with a substantial increase in discharge rate to cold stimuli of 20 degrees C or less. A small temperature rise of 2 degrees C from the normal surface temperature of the testis (34 degrees C) significantly increased the response to hypertonic saline (616 mM) (2.41 +/- 0.22 impulses/s at 34 degrees C to 3.23 +/- 0.44 impulses/s at 36 degrees C) and to bradykinin (9 X 10(-8) M) (1.95 +/- 0.35 impulses/s at 34 degrees C to 2.85 +/- 0.19 impulses/s at 36 degrees C). The majority of the units recorded from the superior spermatic nerve in this experiment were most probably of polymodal receptor type, although the heat response was tested in a limited number of units. A very small number of a different type of receptor was discovered: rapidly adapting mechano-receptors, which responded almost exclusively to mechanical stimulation and were especially sensitive to a light mechanical stimulus moving across the receptive fields. The response properties of receptors studied in vitro remained practically unchanged during the experiments of several hours. The present experiments have shown that this preparation is suitable for systematic investigations, especially of the effects of chemical agents, on the polymodal receptor, which plays important roles in nociceptive functions.
Low extracellular magnesium induces epileptiform activity and spreading depression in rat hippocampal slices
Authors: Mody I. , Lambert J. D. , Heinemann U.
Published: December 2017

The effect of low extracellular Mg2+ concentration ([Mg2+]o) on neuronal activity was studied in rat hippocampal slices. After 20–40 min of perfusion with Mg2+-free medium, when [Mg2+]o declined to approximately 0.1–0.4 mM, spontaneous field potentials developed in the CA1 and CA3 regions, but not in the dentate gyrus. In the CA3 pyramidal cell layer, these potentials consisted of repetitive (0.3–0.5 Hz), 40- to 120-ms-long positive deflections (2–5 mV) with superimposed population spikes. In the stratum (str.) pyramidale of the CA1 region, positive-negative deflections (less than 3 mV) lasting for 30–80 ms were observed, which occurred with a frequency of 0.3-0.5 Hz. In some cases, longer lasting and rapidly recurring events were also observed. In CA3 pyramidal cells, the intracellular correlates of the field potential transients were 20- to 30-mV paroxysmal depolarization shifts (PDS) with superimposed bursts of action potentials, followed by large (greater than 10 mV), 500- to 1,200-ms-long afterhyperpolarizations (AHP). In contrast, pyramidal neurons of the CA1 area did not show PDSs; instead, sequences of excitatory postsynaptic potentials (EPSPs)/inhibitory postsynaptic potentials (IPSPs) accompanied the transient field potential changes. Occasionally, spontaneous EPSPs/IPSPs, occurring with high frequencies, could also be observed in CA1 without any field potential transients. In both hippocampal regions, the epileptiform activity evolved without significant alterations in the resting membrane potential (RMP) and input resistance (RN) of the neurons, although a 2- to 5-mV reduction in action potential threshold was noted. The spontaneous activity in Mg2+-free medium was readily suppressed by raising the extracellular Ca2+ concentration ([Ca2+]o) from 1.6 to 3.6 mM. The perfusion of 10-30 microns DL-2-amino-5-phosphonovaleric acid (2-APV), an antagonist for the glutamate receptors of the N-methyl-D-aspartate (NMDA) type, also attenuated or reversibly blocked the spontaneous activity. Surgical isolation of area CA1 from CA3 ceased the occurrence of the transients in CA1 but not in CA3. The synaptic input/output curves were shifted to the left in the absence of [Mg2+]o. Threshold intensity for eliciting population spikes was 50-75% of that in normal medium. Paired-pulse facilitation was still present near threshold, but was reduced at higher stimulus intensities. Decreases in [Ca2+]o, produced by repetitive stimulation (20-Hz/5-10 s) of the Schaffer collateral/commissural pathway and monitored with ion-selective microelectrodes in the CA1 region, were enhanced in Mg2+-free medium.(ABSTRACT TRUNCATED AT 400 WORDS)
Functional associations among simultaneously monitored lateral medullary respiratory neurons in the cat. II. Evidence for inhibitory actions of expiratory neurons
Authors: Lindsey B. G. , Segers L. S. , Shannon R.
Published: December 2017

Arrays of extracellular electrodes were used to monitor simultaneously several (2-8) respiratory neurons in the lateral medulla of anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Efferent phrenic nerve activity was also recorded. The average discharge rate as a function of time in the respiratory cycle was determined for each neuron. Most cells were tested for spinal or vagal axonal projections using antidromic stimulation methods. Cross-correlational methods were used to analyze spike trains of 480 cell pairs. Each pair included at least one neuron most active during the expiratory phase. All simultaneously recorded neurons were located in the same side of the brain stem. Twenty-six percent (33/129) of the expiratory (E) neuron pairs exhibited short time scale correlations indicative of paucisynaptic interactions or shared inputs, whereas 8% (27/351) of the pairs consisting of an E neuron and an inspiratory (I) cell were similarly correlated. Evidence for several inhibitory actions of E neurons was found: 1) inhibition of I neurons by E neurons with both decrementing (DEC) and augmenting (AUG) firing patterns; 2) inhibition of E-DEC and E-AUG neurons by E-DEC cells; 3) inhibition of E-DEC and E-AUG neurons by E-AUG neurons; and 4) inhibition of E-DEC neurons by tonic I-E phase-spanning cells. Because several cells were recorded simultaneously, direct evidence for concurrent parallel and serial inhibitory processes was also obtained. The results suggest and support several hypotheses for mechanisms that may help to generate and control the pattern and coordination of respiratory motoneuron activities.
Binaural processing of sound pressure level in the inferior colliculus
Authors: Semple M. N. , Kitzes L. M.
Published: December 2017

The central auditory system could encode information about the location of a high-frequency sound source by comparing the sound pressure levels at the ears. Two potential computations are the interaural intensity difference (IID) and the average binaural intensity (ABI). In this study of the central nucleus of the inferior colliculus (ICC) of the anesthetized gerbil, we demonstrate that responses of 85% of the 97 single units in our sample were jointly influenced by IID and ABI. For a given ABI, discharge rate of most units is a sigmoidal function of IID, and peak rates occur at IIDs favoring the contralateral ear. Most commonly, successive increments of ABI cause successive shifts of the IID functions toward IIDs favoring the ipsilateral ear. Neurons displaying this behavior include many that would conventionally be classified EI (receiving predominantly excitatory input arising from one ear and inhibitory input from the other), many that would be classified EE (receiving predominantly excitatory input arising from each ear), and all that are responsive only to contralateral stimulation. The IID sensitivity of a very few EI neurons is unaffected by ABI, except near threshold. Such units could provide directional information that is independent of source intensity. A few EE neurons are very sensitive to ABI, but are minimally sensitive to IID. Nevertheless, our data indicate that responses of most EE units in ICC are strongly dominated by excitation of contralateral origin. For some units, discharge rate is nonmonotonically related to IID and is maximal when the stimuli at the two ears are of comparable sound pressure. This preference for zero IID is common for all binaural levels. Many EI neurons respond nonmonotonically to ABI. Discharge rates are greater for IIDs representative of contralateral space and are maximal at a single best ABI. For a subset of these neurons, the influence arising from the ipsilateral ear is comprised of a mixture of excitation and inhibition. As a consequence, discharge rates are nonmonotonically related not only to ABI but also to IID. This dual nonmonotonicity creates a clear focus of peak response at a particular ABI/IID combination. Because of their mixed monaural influences, such units would be ascribed to different classes of the conventional (EE/EI) binaural classification scheme depending on the binaural level presented. Several response classes were identified in this study, and each might contribute differently to the encoding of spatial information.(ABSTRACT TRUNCATED AT 400 WORDS)
A kinematic and electromyographic study of cutaneous reflexes evoked from the forelimb of unrestrained walking cats
Authors: Drew T. , Rossignol S.
Published: December 2017

A kinematic and electromyographic (EMG) analysis was undertaken of the responses evoked in the forelimb of the cat by either mechanical obstruction of the forelimb during the swing phase of locomotion or by electrical stimulation of low-threshold cutaneous afferents during both swing and stance. Mechanical obstruction of the forelimb with a stiff metal rod evoked a complex response that allowed the cat to smoothly negotiate the obstacle without undue disruption of the overall locomotor rhythm. The initial movements were a flexion of the shoulder, together with a locking of the elbow joint, and a dorsiflexion of the wrist, which caused the limb to withdraw from the obstacle. They were followed by an extension of the shoulder, a flexion of the elbow, and a ventroflexion of the wrist, which together brought the limb forward and above the obstacle. The associated and complex pattern of short- and long-latency EMG responses was shown to be related to different aspects of the movement. At the shoulder there was a strong activation of flexor muscles; these responses were of long duration (greater than or equal to 100 ms) and generally lasted throughout the period of shoulder flexion. At the elbow, both flexor and extensor muscles were activated at short latency (9-13 ms). In flexors, this was followed by a cessation and subsequently an augmentation and prolongation of their activity. Dorsiflexors of both the wrist and digits were activated at short latency (10-12 ms) and remained active throughout the period of dorsiflexion of these joints. An injection of a local anesthetic into the area of skin contacted by the metal rod reduced or abolished all of the reflex responses, which suggests that the integrity of cutaneous reflex pathways is essential for the elaboration of these responses. Electrical stimulation of a cutaneous nerve innervating the distal forelimb (the superficial radial nerve) resulted in qualitatively similar, although weaker, responses to those obtained with the mechanical stimulation. Terminal experiments confirmed that these responses were mediated by low-threshold cutaneous afferents. Electrical stimulation also evoked short-latency excitatory responses (10-12 ms) in extensor muscles of the elbow. Generally, the largest reflex effects were obtained during the period of swing for flexor, extensor, and bifunctional muscles. During stance the stimulus was normally ineffective in exciting flexor muscles and in extensors evoked a short-latency inhibition, which was frequently followed by an increase in activity.(ABSTRACT TRUNCATED AT 400 WORDS)