bluuebunny/crossref_metadata_2025 huggingface dataset:
Depth distribution of neuronal activity related to a visual reaction time task in the monkey prefrontal cortex
Authors: Sawaguchi T. , Matsumura M. , Kubota K.
Published: December 2017

1. The depth distributions of neurons with changes in activity during a visual reaction time task were investigated in the dorsolateral prefrontal cortex of the macaque monkey, using glass micropipettes. The task was initiated by the monkey pressing a lever and consisted of an initial waiting phase (3.0-s period); a warning phase (green lamp, a variable period of 1.5-3.5 s); a lever-release GO phase (red lamp); and a final reward phase. The locations of neurons, in terms of the cortical layer, whose activities were recorded during performance of the task, were estimated histologically by marks made during the recording session. Marks were made by passing a DC current (anodal, 10-20 microA, 10-20 s) through the tip of an electrode which contained carbon fibers. Manipulator readings during the experiments and measurements of the distance of the marks from the cortical surface for 28 electrode penetrations showed a discrepancy of 2.0 +/- 5.0%, indicating that the depths at which task-related neurons were located could be estimated with errors of less than 10%. 2. Out of 162 task-related neurons recorded during 31 electrode penetrations, 53 showed changes in activity only during the warning phase (W-type; 19 phasic, 10 phasic-tonic, and 24 tonic), 37 showed changes only during the GO phase (GO-type; 4 Cue-coupled, 27 Intermediate, and 6 Movement-coupled), 34 showed changes during both the warning and GO phases (WG-type; 9 phasic, 10 phasic-tonic, and 15 tonic), and 38 showed changes during the reward phase (RE-type; 22 phasic and 16 tonic). 3. The various task-related neurons were distributed differently in different layers. Most neurons were recorded from layers III through V. In layer I, no neurons were recorded. In layer II, only a small number of neurons, with changes during the warning phase, were recorded (n = 7, 4%). One-third of the neurons were recorded in layer III (n = 51, 32%); neurons with changes during the warning phase were the most numerous (n = 24) and were significantly more numerous than neurons with changes associated with other phases of the task. One-fourth of the neurons were recorded in layer IV (n = 43, 27%); neurons with changes during the reward phase were the most numerous (n = 19), and were significantly more numerous than neurons with changes during both the warning and GO phases and also more numerous than neurons with changes during the GO phase.(ABSTRACT TRUNCATED AT 400 WORDS)
Components of responses of a population of DSCT neurons to muscle stretch and contraction
Authors: Osborn C. E. , Poppele R. E.
Published: December 2017

1. Impulse activity of 264 units of the dorsal spinocerebellar tract (DSCT) was recorded during random contraction or stretch in hindlimb muscles. Contractions were evoked in either the isolated gastrocnemius-soleus (GS) muscles or the intact limb during crossed-extensor reflexes; stretches were applied to the isolated GS. 2. The time course of poststimulus changes in spike activity of DSCT neurons was determined from the response probability function (RPF; Ref. 15). These data were analyzed using principal component and cluster analysis to group the responses according to the RPF waveforms. 3. The responses to each type of stimulus displayed a remarkable similarity in time course, regardless of the type of stimulus used. The responses were also similar to those observed previously during single shock nerve stimulation (14). 4. The most reasonable explanation for these results is that the time course of excitability changes in DSCT neurons is determined less by particular types of receptors or patterns of afferent fiber activity than by the circuitry and afferent pathways impinging on the neurons of the DSCT. 5. The functional organization of DSCT suggested by these results includes a wide divergence from sensory receptors along polysynaptic pathways to DSCT neurons and considerable convergence onto each neuron from a diversity of receptors. Individual DSCT cells may respond to stimuli with one of a few stereo-typical response patterns yet the distribution of those patterns among the units of the DSCT population may be unique for each stimulus.
Cytometric analysis of the thalamic ventralis intermedius nucleus in humans
Authors: Hirai T. , Ohye C. , Nagaseki Y. , Matsumura M.
Published: December 2017

1.The cytoarchitecture and the exact borders of the thalamic ventralis intermedius (Vim) nucleus of humans as originally delineated by Hassler (17) have been studied on the basis of stereotaxic coordinates correlated with Nissl- and Golgi-impregnated sections, using a microscopic image analyzer. 2. The Vim nucleus forms part of a relatively “cell-sparse zone” which includes the other ventrolateral thalamic subnuclei. It is distinguished by the presence of darkly stained, large and medium sized, angular cells with areas of approximately 500–1,000 microns 2 and 300-400 microns 2, respectively, and a cell density of approximately 50-90 (mean 65)/mm2 in 50-microns-thick sections. 3. Both sets of neurons have the characteristics of thalamocortical relay neurons in Golgi preparations. Large neurons have rectangular or square somata 30-50 microns diam and are concentrated mainly in the lateral and ventral two-thirds of the nucleus. The medium neurons have square to round somata, 15–25 microns diam, and are distributed homogeneously through the nucleus. The total dendritic arborization of both types is usually symmetrical in all directions and at least 500–600 microns diam. 4. The borders between the Vim nucleus and the Nucleus ventrooralis (Vo) and between the Vim nucleus and the Nucleus ventrocaudalis internus (Vci) are clearly identified by clearcut differences in cell size and cell density. The borders between the Vim nucleus and the Nucleus ventrooralis internus (Voi) and between the Vim nucleus and the Nucleus zentrolateralis intermedius (Zim) are quite obscure, and these nuclei, with Vim, seem to be parts of the large cell sparse zone comparable to that described in monkeys as VLp or VL. The border between the Vim nucleus and the Nucleus ventrocaudalis externus anterior (Vcea) is also unclear but the increased cell density and intermingling of small and medium-to-small neurons with large neurons are the major features that distinguish the Vcea nucleus from the Vim nucleus cytometrically. 5. The position and anatomic organization of the human Vim nucleus make it likely that it is the region in which kinesthetic response were recorded in the accompanying paper but extension of the recording sites into the Vcea nucleus cannot be ruled out.
Further physiological observations on the ventralis intermedius neurons in the human thalamus
Authors: Ohye C. , Shibazaki T. , Hirai T. , Wada H. , Hirato M. , Kawashima Y.
Published: December 2017

1.During the course of stereotaxic thalamotomy for 56 cases with tremor mainly due to Parkinson's disease and essential tremor, extracellular recordings were made from the thalamic ventralis intermedius (Vim) nucleus under local anesthesia. These procedures have been justified as an essential technique to achieve the best therapeutic results by a selective coagulation. These physiological observations provide important information about the functional organization of the ventrolateral thalamic mass in humans. 2. Using Leksell's stereotaxic apparatus, a pair of semimicroelectrodes was introduced simultaneously to the thalamic ventral lateral region from the prefrontal area. The Vim nucleus was identified tentatively by characteristic high background activity which contrasted to that found in its rostral part and by superimposed large amplitude spontaneously active units. 3. In this high activity zone, 135 units (approximately 1/5 of the recorded units) responded to natural stimulation applied to contralateral body parts. Among them, approximately 90% responded to a passive or active movement of a joint. Several lines of evidence suggested that probably muscle receptors were responsible. 4. The rest of units (approximately 10%) responded to light touch applied to contralateral skin surface. Convergent responses between kinesthetic and tactile units were never encountered. Also, kinesthetic and tactile neurons were geographically separated. The latter were found always at the end of our oblique trajectory, following the kinesthetic neurons. 5. Neurons with sensory responses were clustered mostly within the confines of the Vim nucleus, probably extending caudally to the ventrocaudalis externus anterior of Hassler. Evidence for a somatotopic representation in the Vim nucleus was obtained. 6. Electrical stimulation of the appropriate peripheral nerve produced responses of the same thalamic unit(s) that responded to natural stimulation. The latency to upper limb nerve stimulation was between approximately 10 and 20 ms. It was almost fixed in a given case. 7. It is concluded that the Vim nucleus receives kinesthetic afferent input from the contralateral body parts (mainly from the muscle receptor) and may be concerned with muscle sense. This may explain why a small, selective coagulation of the physiologically identified Vim has such a constant effect on several different kinds of tremor.
Effects of spatial and temporal dispersion of synaptic input on the time course of synaptic potentials
Authors: Walmsley B. , Stuklis R.
Published: December 2017

1. As part of the ongoing studies on the time course of single-fiber synaptic potentials recorded in spinal neurons, a theoretical analysis of the effects of spatial and temporal dispersion of synaptic input to a neuronal cable model was undertaken. 2. Results were obtained using a simple R-C soma, equivalent dendritic cylinder cable model of a neuron. Synaptic input was represented by a current injection at various points on the dendritic cable. 3. Spatial dispersion of multiple inputs to the cable model generally produced somatic transients with smooth time courses that could be closely matched by a transient generated at a single input location, usually with a different current time course. 4. Temporal dispersion, representing nonsynchronous activation of multiple synaptic contacts at the same electrotonic location, generally resulted in somatic transients with an increased rise-time and a corresponding small increase in the half-width. The somatic transient generated by these temporally dispersed inputs could usually be well matched by a single input at a different location. 5. Addition of temporal dispersion to a spatially dispersed input produced variable results in which the rise-times and half-widths of somatically recorded transients could be either increased or decreased. 6. It is concluded that a detailed knowledge of both the spatial and temporal properties of synaptic input is essential to the interpretation of single-fiber synaptic potentials. Previous results on the amplitude and time course of single-fiber synaptic potentials recorded in spinal neurons are discussed in light of the present observations.
Effects of prolonged light exposure, GABA, and glycine on horizontal cell responses in tiger salamander retina
Authors: Yang X. L. , Wu S. M.
Published: December 2017

1. The effects of prolonged light exposure, gamma-aminobutyric acid (GABA), and glycine on the horizontal cell (HC) light responses were studied in the superfused flat-mounted isolated retinas of the larval tiger salamander. 2. Under prolonged dark-adapted conditions, the time-to-peak of the HC light response was approximately 2-4 s, and after the termination of prolonged (6-8 min) light exposure, the time-to-peak became approximately 0.5-1 s. 3. This prolonged light-induced change in response rise time was not observed in either photoreceptors or bipolar cells, and thus the change in HC response rise time may occur postsynaptically in the HC membrane. 4. Application of 100 microM of GABA mimicked prolonged darkness and reversibly slowed down the HC response rise time, and application of 100 microM bicuculline mimicked prolonged light exposure and reversibly sped up the HC response rise time. 5. Glycine also slowed down the HC response rise course, but its effect was not observable until the concentration was raised to 1-3 mM. Strychnine did not exert any effect on HC responses when applied alone, but it could reverse the glycine actions. 6. The actions of glycine disappeared in the presence of bicuculline, indicating that the GABA and glycine pathways were probably not independent. Application of 5-10 mM glycine produced an increase of flow of preloaded 3H-GABA from the retina. 7. These results indicate that GABA may be the primary modulator that slows down the kinetics of the postsynaptic membrane proteins in the HCs. The extracellular concentration of GABA is probably high in prolonged darkness, and it is low after prolonged light exposure. Glycine, when applied at high dose, results in an increase of GABA release that slows down the HC response time course. 8. Prolonged darkness and light exposure appear to modulate the HC response in the time domain through GABA, and this change in HC response time course is probably responsible for shaping the bipolar cell responses and making the retinal signals more transient under light-adapted conditions.
Innervation of vascular and cardiac muscle of Aplysia by multimodal motoneuron L7
Authors: Alevizos A. , Bailey C. H. , Chen M. , Koester J.
Published: December 2017

1. The cardiovascular system of Aplysia has proven to be a useful preparation for study of the neural control of circulation. To better understand the neural integration of function in this system, we have attempted to gain a more complete picture of its morphology and innervation patterns, with particular emphasis on the abdominal aorta and heart. 2. The vasoconstrictor muscle fibers of the abdominal aorta were found by dye injection to be extensively branched, with many processes that are less than 1 micron in diameter. Because of the wide spacing between individual muscle fibers, these fine processes, which have relatively few contractile filaments, may be required to mediate the electrical coupling that is observed between muscle cells. 3. L7, an identified cell in the abdominal ganglion, had been shown by others to be an excitatory motoneuron for the gill, the siphon, and the sheath-contracting muscles of the pleuroabdominal connectives, and also to excite the gill motoneurons in the branchial ganglion (5, 43, 56). We have found that this multimodal motoneuron also directly excites the auricle of the heart and the vasoconstrictor muscle of the abdominal aorta. 4. The excitatory effect of L7 on the abdominal aorta interacts synergistically with that produced by the other known excitatory inputs to that structure, the LBVc vasoconstrictor motoneurons. 5. The abdominal aorta is also richly innervated by axons immunoreactive for serotonin and for the neuropeptide FMRFamide. Serotonin inhibits the contractions of the aorta elicited by firing either L7 or the LBVC cells. In contrast, FMRFamide selectively inhibits the contractions elicited by the LBVC cells. 6. Our results suggest that a significant amount of the functional integration of the cardiovascular and respiratory systems is achieved by the use of a motoneuron common to both systems, and that there is likely to be extensive peripheral inhibitory modulation of the vasoconstrictor inputs to the abdominal aorta.
Patterns of resting discharge in neurons of the raccoon main cuneate nucleus
Authors: Pubols B. H. , Haring J. H. , Rowinski M. J.
Published: December 2017

1. The presence and pattern of resting discharge were examined in 100 single neurons of the raccoon main cuneate nucleus (MCN). Of these, 66 were activated, either antidromically or synaptically, by electrical stimulation of the contralateral thalamic ventrobasal complex (VB), and 34 were activated by stimulation of the ipsilateral cerebellum (CB). 2. Forty-one percent of VB-activated neurons displayed a resting discharge, whereas 32% of CB-activated neurons did. Most neurons activated from VB and showing a resting discharge fired in bursts of 2-5 spikes, whereas those activated from CB and showing a resting discharge generally fired as single, irregularly spaced spikes, with occasional bursts in some neurons. 3. All neurons antidromically activated from VB were histologically localized within the clusters region of the MCN, whereas those antidromically activated from CB were confined to its polymorphic region. Neurons synaptically activated from either VB or CB were located in either of these regions. 4. Differences in the proportions of neurons displaying a resting discharge did not vary significantly as a function of type of preparation: methoxyflurane anesthesia, pentobarbital sodium anesthesia, decerebrate (the latter CB-activated only). 5. Although the sample sizes were too small to demonstrate statistical significance, neurons exhibiting a resting discharge were more likely to show a bursting pattern in methoxyflurane-anesthetized preparations than were neurons in pentobarbital sodium-anesthetized preparations. 6. The probability of having no resting discharge, firing in bursts, or firing in single spikes was not related to cutaneous submodality [rapidly adapting (RA), slowly adapting (SA), Pacinian (Pc)], or to receptive field (RF) locus (glabrous versus hairy skin). 7. The overall mean rate of firing (11.8 Hz) was not significantly different for bursting versus nonbursting neurons. 8. In bursting neurons, median interspike intervals (ISIs) varied between 1.3 and 2.3 ms. Most bursting neurons also had a range of short or minimal interburst intervals (MIBIs), characteristic for each neuron, whose medians varied from neuron to neuron between 34 and 90 ms. Distributions of within-burst ISIs and MIBIs had comparable coefficients of variation, varying between 0.031 and 0.223. 9. The application of a mechanical stimulus to a neuron's peripheral RF led to a decrease in interburst intervals, accompanied, depending upon the unit, by either an increase or a decrease in the number of spikes per burst. 10. Results are discussed in terms of the functional significance of resting discharge, including bursting, and possible roles in somatosensory information
Discharge patterns of rostrolateral medullary expiratory neurons in the cat: regulation by concurrent network processes
Authors: Lindsey B. G. , Segers L. S. , Shannon R.
Published: December 2017

1. The identification of numerous functional connections among medullary respiratory related neurons led us to postulate specific short time scale correlations among neuronal spike trains consistent with 1) inhibition of rostrolateral medullary augmenting expiratory (E-AUG) neurons by other E-AUG cells, and 2) inhibitory control of the postulated E-AUG neural network by decrementing expiratory (E-DEC) neurons. Recent observations of reduced rostrolateral E-AUG cell activity following stimulation of sensory afferents raised the additional question of whether reflex control mechanisms use the identified functional connections to mediate their effects. 2. Experiments were conducted on 42 anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Impulse trains of two or more respiratory related neurons of the lateral medulla, including at least one rostrolateral medullary E-AUG neuron, were simultaneously recorded together with phrenic nerve efferent activity. Most neurons were tested for spinal axonal projections with antidromic stimulation methods. In some experiments, the central cut end of the right vagus nerve was electrically stimulated during the expiratory interval. Data were analyzed using cycle-triggered histograms, auto- and cross-correlograms, logical cross-correlograms, snowflake scatter diagrams, and peristimulus time histograms. 3. Seven of 73 pairs (9.6%) of ipsilateral E-AUG neurons exhibited short time scale correlations in firing probability. Two rostral pairs had coincident increases in activity. Five pairs were characterized by a reduction in activity in a rostral neuron following spikes in the other cell; concurrent serial inhibition among one set of three E-AUG neurons was indicated. These five pairs, together with three other similarly correlated pairs described previously, were studied further: spikes recorded during the first and second halves of the expiratory (E) phase were analyzed separately. This phase segmentation unmasked multiple correlations implying reciprocal inhibition between one pair of E-AUG neurons. Short time scale troughs in correlograms generated from late E-phase spike trains had significantly (P less than 0.05) greater detectability indices than troughs in early E-phase correlograms. Multineuron correlations revealed two cases in which the firing probability of the target E-AUG neuron was reduced less when only reference E-AUG cell spikes coincident with spikes in a third, E-DEC, neuron were used as trigger events. 4. Enhanced rostral E-AUG neuron firing probabilities coincident with or following impulses in ipsilateral E-DEC neurons were detected in 6 of 94 (6.4%) rostral pairs.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of tooth pulp deafferentation on nociceptive and nonnociceptive neurons of the feline trigeminal subnucleus caudalis (medullary dorsal horn)
Authors: Hu J. W. , Sessle B. J.
Published: December 2017

1. Effects of deafferentation of the tooth pulps of the posterior mandibular teeth were studied in single neurons recorded in the ipsilateral subnucleus caudalis of the trigeminal (V) spinal tract nucleus of adult cats and kittens. The functional properties of neurons in each anesthetized animal were determined electro-physiologically in a series of microelectrode penetrations of the subnucleus. 2. The more than 800 neurons investigated could be subdivided on the basis of their cutaneous mechanoreceptive field properties into low-threshold mechanoreceptive (LTM) neurons, wide dynamic range (WDR) neurons, or nociceptive-specific (NS) neurons. Comparisons of neuronal properties were made between control (intact) cats and 7-15 day deafferented cats studied in a blind design, as well as groups of longer term deafferented cats, and kittens undergoing a “natural” deafferentation as a result of exfoliation of primary teeth. 3. There was no apparent change in the somatotopic pattern of organization of the subnucleus in the kittens and pulp-deafferented cats and no statistically significant differences were noted between kittens and control cats in any property except for alterations in the incidence of spontaneously active neurons. 4. Limited but statistically significant alterations were noted in some of the neuronal properties in the deafferented cats. These changes were especially apparent in the LTM neurons. The incidence of spontaneous activity was significantly decreased in the neurons of most long-term deafferented groups of cats. In the 7–15 day deafferented group, significantly more LTM neurons had a mechanoreceptive field involving all three divisions of the V nerve, and there was a significant increase in the incidence of LTM neurons activated by electrical stimulation of intraoral sites. Mechanosensitive neurons responsive only to tap stimuli were found only in the deafferented groups of cats. 5. These alterations in caudalis contrast with previous reports claiming marked hyperexcitability of caudal V brain stem neurons as a consequence of deafferentation and implicating such effects in the development of pain. However, some of the changes are in general not inconsistent with deafferentation-induced changes reported in spinal somatosensory neurons and with the pulp deafferentation-induced changes that we have recently documented in LTM neurons of subnucleus oralis of the V spinal tract nucleus of adult cats.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of ionic calcium on the responses of canine testicular polymodal receptors to algesic substances
Authors: Sato J. , Mizumura K. , Kumazawa T.
Published: December 2017

1. To explore possible mechanisms of the responses to algesic substances (bradykinin, hypertonic saline, and high K+ solution) of polymodal receptors in the canine testis, the Ca2+ concentration was varied in vitro. 2. After 1 min in Ca2+-free media, the responses to both high K+ solution (60 mM K+) and hypertonic saline (0.6 M Na+) were significantly augmented and tended to increase further with time; return to normal Ca2+ concentration quickly reversed these changes. These augmenting effects were blocked by the substitution of Mg2+ for Ca2+. The excitation produced by 60 mM K+ was decreased by increasing Ca2+ in a concentration-dependent fashion. 3. Reducing the bath concentration of K+ decreased responses evoked by 9 X 10(-8) M bradykinin (BK), whereas increased K+ concentration had the opposite effect. 4. The excitatory effects of BK were significantly suppressed in extracellular Ca2+-free condition. The suppression was not affected by the addition of Mg2+. Prostaglandin E2, which has been known to be released by BK and to augment the BK response, failed to restore the suppressed response by either preapplication (2.8 X 10(-7) M) or simultaneous application in high concentration (1.4 X 10(-5) M). 5. On the basis of these observations, it was postulated that Ca2+ concentration-dependent changes of the responses to 60 mM K+ and 0.6 M Na+ results from Ca2+-dependent "membrane surface potential" changes. The suppressed response to BK by Ca2+ depletion may be explained by the intervention of Ca2+-dependent processes other than PG production.
Binocular interactions in the cat's dorsal lateral geniculate nucleus. I. Spatial-frequency analysis of responses of X, Y, and W cells to nondominant-eye stimulation
Authors: Guido W. , Tumosa N. , Spear P. D.
Published: December 2017

1. X, Y, and W cells in the A and C layers of the cat's dorsal lateral geniculate nucleus (LGN) were tested for responses to stimulation of the nondominant eye. The main purpose was to determine the incidence of nondominant-eye excitation and inhibition among different classes of cells and to examine the spatial-frequency tuning of responses to the nondominant eye. 2. Of 198 cells that were tested with drifting sine-wave gratings presented to the nondominant eye, 109 (55%) showed statistically significant responses. Four types of responses were observed: an increase in the mean discharge rate (F0 excitation), a decrease in the mean discharge rate (F0 inhibition), an increased modulation at the fundamental frequency of the grating (F1 excitation), and a decreased modulation at the fundamental frequency of the grating (F1 inhibition). Overall, 29% of the cells responded with inhibition, 24% responded with excitation, and 2% showed both excitation and inhibition, depending upon the spatial frequency and/or the harmonic response component. The relative incidence of excitation and inhibition was similar for X, Y, and W cells, for cells with on-center and off-center receptive fields, for cells with different receptive-field eccentricities, and for cells in each LGN layer. In addition, within layers A and A1, responses were similar for cells at different distances from the laminar borders. 3. Spatial-frequency response functions indicated that cells could have band-pass or low-pass spatial-frequency tuning through the nondominant eye. Band-pass cells tended to be narrowly tuned (less than or equal to 1 octave), and low-pass cells responded to a broader range of spatial frequencies. These properties were similar for X, Y, and W cells. Spatial resolution tended to be low (less than or equal to 0.8 c/deg for most cells), although a few cells responded to the highest spatial frequency tested (5.4 c/deg). Likewise, optimal spatial frequency was low (less than or equal to 0.2 c/deg) for most cells. These properties were similar for X and Y cells, and there was a weak tendency for X and Y cells to have higher optimal spatial frequencies and spatial resolutions than W cells. 4. In terms of absolute change in activity, responses to drifting gratings were weak. However, cells that were inhibited generally showed 20-60% decreases in activity to the optimal spatial frequency, and cells that were excited generally showed 40-100% increases. Response amplitudes were similar for X, Y, and W cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Two components of rapid sensory adaptation in a cockroach mechanoreceptor neuron
Authors: French A. S.
Published: December 2017

1. The femoral tactile spine of the cockroach is innervated by a single sensory neuron with its cell body in the spine. A step deflection of the spine produces a burst of action potentials which decays to zero in approximately 1 s. This rapid adaptation occurs during encoding of action potentials and can be studied by extracellular electrical stimulation of the sensory neuron. 2. The threshold current of the neuron is labile, increasing with depolarization and decreasing with mild hyperpolarization. During rapid adaptation, the threshold current increases to exceed any steady stimulating current. 3. The dynamic behavior of the threshold current in the tactile spine neuron was observed following step changes in membrane current. The threshold current followed a trajectory which could always be well fitted by a sum of two exponential decays with time constants of approximately 100 and 1,000 ms. 4. The amplitude of the slow component of threshold change was proportional to the size of the step change in membrane current but saturated at strong hyperpolarizations. Its time constant decreased monotonically with depolarization. In contrast, the fast component had more complex behavior, changing biphasically with step amplitude and reversing with initial hyperpolarizations. Its time constant was maximal at the resting membrane potential. 5. The amplitude of the fast component was strongly reduced by treatment with N-chlorosuccinimide (NCS), an agent which reduces sodium channel inactivation. It was not affected by some agents known to block potassium channels. 6. The slow component was not affected by NCS, tetraethyl-ammonium chloride, apamin, or charybdotoxin. 7. Approximate contributions of the two components to the steady-state threshold were reconstructed from step responses. These indicate that the slow component dominates when the receptor is hyperpolarized. However, during depolarizations from rest, as occur with normal stimulation, the two components contribute approximately equally to threshold changes.
Unilateral auditory cortex ablation in macaques results in a contralateral hearing loss
Authors: Heffner H. E. , Heffner R. S.
Published: December 2017

1. The behavioral audiograms of four Japanese macaques (Macaca fuscata) were assessed before and after unilateral ablation of auditory cortex. The tones were presented via insertion earphones so that each ear could be tested separately. 2. Each animal had a hearing loss in the ear contralateral to the lesion, whereas the ipsilateral ear showed no change in sensitivity. The hearing loss initially appeared as a large shift in thresholds followed by rapid but incomplete recovery during the first 3-5 wk after surgery. The initial hearing loss ranged as high as 68 dB at some frequencies, although thresholds at other frequencies were occasionally unchanged. A threshold shift could be demonstrated with broadband noise as well as with tones. Although thresholds for some tones returned to normal within a few weeks, most were still elevated 16 wk after surgery when testing was discontinued. The largest long-term hearing losses occurred at frequencies from 4 to 25 kHz. 3. Analysis of the animals' psychophysical functions suggested that the hearing loss resembled a sensory deficit, as opposed to a nonsensory deficit in attention or vigilance. 4. Testing with binaural stimuli indicated that the hearing loss could best be described as a contralateral "ear" deficit, as opposed to a contralateral "auditory field" deficit. 5. It is suggested that a similar hearing loss occurs in humans after unilateral damage to auditory cortex.
Photoreceptor to horizontal cell synaptic transfer in the Xenopus retina: modulation by dopamine ligands and a circuit model for interactions of rod and cone inputs
Authors: Witkovsky P. , Stone S. , Tranchina D.
Published: December 2017

1. In the Xenopus retina, the effects of selective D1 and D2 dopamine ligands on photoreceptor to horizontal cell transfer were studied by intracellular recording from horizontal cell axons. Rod and cone inputs to the horizontal cell were estimated by adjusting the intensities of red and green flashes to elicit equal rod tails. The resultant waveforms were digitized and subtracted, and their difference was taken to reflect solely cone input to the horizontal cell. 2. It was found that both D1 (SKF 38393) and D2 (LY 171555) agonists increased the amplitude and quickened the kinetics of cone-to-horizontal cell transfer; they also depolarized the horizontal cell by 8-10 mV. In contrast, either D1 or D2 agonists reduced the rod input to the horizontal cell without altering its kinetics. 3. Type D2 antagonists reduced and slowed the cone input and hyperpolarized the horizontal cell. D2 antagonists increased the rod input but left its kinetics unchanged. 4. Although both D1 and D2 agonists elicited qualitatively similar effects, the D1 agonist evoked a greater increase in the amplitude and a greater acceleration of the kinetics of the cone input than did the D2 agonist. Moreover, the action of the D1 agonist was blocked by SCH 23390 but not by spiroperidol or metoclopramide, whereas the reverse was true for the D2 agonist. These data indicate that D1 and D2 agonists probably act at different sites. 5. The pharmacologic findings are interpreted to indicate that dopamine ligands act primarily through the cone pathway and that rod-to-horizontal cell transfer is shunted to a variable degree. 6. An equivalent circuit model was developed for a spine-bearing portion of a horizontal cell axon of the Xenopus retina. Anatomic study shows that such spines branch, making contact with both rod and cone photoreceptor bases. Thus there are two conductance pathways in parallel for rod-to-horizontal cell and cone-to-horizontal cell transmission. The model is used to test the hypothesis that mutual shunting in the two pathways can account for the physiological effects observed. 7. The values of the purely resistive elements of the pathway are based on their dimensions. Membrane resistance was taken to be 5,000 omega/cm2 and axial resistance 200 omega/cm. The photoreceptor-to-horizontal cell synaptic battery was taken to be composed of glutamate-sensitive channels, with unitary channel conductance of 6 pS. Channel density was estimated from freeze-fracture data at 5,000 microns-2. A potassium battery and a glycine-sensitive synaptic input from an interplexiform cell were modeled to exist in parallel with the light-sensitive battery. 8. Dopamine was assumed to increase the conductance of the cone-to-horizontal cell synapse, but not to affect the conductance of the rod-to-to-horizontal cell synapse, consistent with physiological measures.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanics of stretch in activated crustacean slow muscle. II. Dynamic changes in force in response to stretch
Authors: Chapple W. D.
Published: December 2017

1. The mechanical dynamics of the ventral superficial muscles (VSM) of the abdomen of the hermit crab, Pagurus pollicarus, have been analyzed to develop a quantitative model of gradedly excitable arthropod muscle. Such a model is important for understanding the role of proprioceptive reflexes in posture and movement. 2. The decay in force produced after ramp stretch of both passive and active muscle was approximated by the use of regression equations involving a direct term and one to three exponential terms. A second-order equation produced an acceptable description of this decay over short (0.5 s) sampling durations. 3. The rate constants of the regression equation did not vary with stretch length, velocity, or activation level of the muscle. For the two-exponential-term model, the rate constants were approximately 90 and 9 s-1 for a sample duration of 0.3 s. An additional rate constant of approximately 1 s-1 was needed to adapt the model to longer sample times. 4. The direct term and the middle-order (9 s-1) residual were both functions of stretch length and activation level. The high-order (90 s-1) residual was primarily a function of stretch length and velocity. Transfer functions omitting the velocity dependence adequately described the mechanical dynamics of the muscle for physiological ranges of stretch velocity. 5. White-noise length perturbations were used to calculate spectral density functions of muscle force and length. These measurements confirmed the principal observations of the ramp stretch analysis: the frequency response of the muscle was independent of the level of activation; the magnitude of the stiffness increased over the stretch frequency range of 4-40 Hz and was then almost constant; and the phase response of the muscle became slightly positive over the same range of stretch frequency. 6. The speed of activation of the muscle to different stimulus frequencies was estimated by fitting a single exponential equation to the rise in isometric tension at the onset of stimulation of the motor nerve. The rate constant increased with stimulus frequency, but its maximum value was only 1.8 s-1, about one-fourth of the middle mechanical rate constant. 7. Because muscle activation is slower than the mechanical dynamics, it is unlikely that the nervous system can regulate muscle dynamics. However, it is possible that mechanical impedance could be regulated to maintain a desired time-averaged value.
Task and fatigue effects on low-threshold motor units in human hand muscle
Authors: Enoka R. M. , Robinson G. A. , Kossev A. R.
Published: December 2017

1. The activity of single motor units was recorded in the first dorsal interosseus muscle of human subjects while they performed an isometric ramp-and-hold maneuver. Motor-unit activity was characterized before and after fatigue by the use of a branched bipolar electrode that was positioned subcutaneously over the test muscle. Activity was characterized in terms of the forces of recruitment and derecruitment and the discharge pattern. The purpose was to determine, before and after fatigue, whether motor-unit activity was affected by the direction in which the force was exerted. 2. Regardless of the task during prefatigue trials, interimpulse intervals were 1) more variable during increases or decreases in force than when force was held constant at the target value (4-6% above the recruitment force), and 2) more clustered around an arbitrary central value than would be expected with a normal (Gaussian) distribution. Both effects were seen during the flexion and abduction tasks. The behavior of low-threshold motor units in first dorsal interosseus is thus largely unaffected by the direction of the force exerted by the index finger. The absence of a task (i.e., a direction of force) effect suggests that the resultant force vector about the metacarpophalangeal joint of the index finger is not coded in terms of discrete populations of motor units, but, rather, it is based on the net muscle activity about the joint. 3. Motor-unit behavior during and after fatigue showed that the relatively homogeneous behavior seen before fatigue could be severely disrupted. The fatiguing protocol involved the continuous repetition, to the endurance limit, of a 15-s ramp-and-hold maneuver in which the abduction target force was 50% of maximum and was held for 10-s epochs (ramps up and down were approximately 2 s each). Motor-unit threshold was assessed by the forces of recruitment and derecruitment associated with each cycle of the fatigue test. Changes in recruitment force during the protocol were either minimal or, when present, not systematic. In contrast, the derecruitment force of all units exhibited a marked and progressive increase over the course of the test. 4. After the fatigue test, when the initial threshold tasks were repeated, the behavior of most motor units changed. These changes included the derecruitment of previously active motor units, the recruitment of additional motor units, and an increased discharge variability of units that remained recruited. The variation in recruitment order seemed to be much greater than that reported previously for nonfatiguing conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
Glycine-gated chloride current in acutely isolated rat hypothalamic neurons
Authors: Akaike N. , Kaneda M.
Published: December 2017

1. Electrical and pharmacologic properties of glycine-induced currents were investigated in single hypothalamic neurons acutely isolated from young and adult rats by the use of a "concentration-clamp" technique, which allows both internal perfusion and rapid application of an external solution under single-electrode voltage-clamp. 2. The glycine-induced current reversed at the Cl- equilibrium potential (ECl), and a 10-fold decrease of extracellular Cl- with a large impermeable anion resulted in a 53 mV shift of the glycine reversal potential (EGly). 3. Glycine-induced Cl- currents (ICl) increased sigmoidally in a concentration-dependent manner with a Kd of 9 X 10(-5) M at a Hill coefficient of 1.8. Current inactivation occurred completely at all concentrations within 10 s. EGly remained unchanged during continuous application of glycine, suggesting that the inactivation process is because of desensitization. 4. The glycine-induced conductance exhibited a striking voltage dependency at membrane potentials more negative than -50 mV and reached a steady state value when hyperpolarized beyond -110 mV. 5. Both the activation and inactivation phases of glycine-induced ICl are described by double exponential (fast and slow components) functions with the concentrations used. All four time constants decreased with increasing glycine concentration. 6. The slow time constant of the current decay induced by glycine increased with depolarization and decreased with hyperpolarization, indicating that the rate of desensitization is considerably voltage dependent. The fast decay showed little voltage dependency. 7. Recovery of the glycine response after complete desensitization consisted of two components. 8. The blockade of the glycine response by strychnine and picrotoxin was noncompetitive.
Effects of excitatory amino acid antagonists on synaptic responses of supraoptic neurons in slices of rat hypothalamus
Authors: Gribkoff V. K. , Dudek F. E.
Published: December 2017

1. Intracellular recordings from magnocellular neurons in the supraoptic nucleus (SON) were obtained from rat hypothalamic slices to determine the effects of specific transmitter antagonists on evoked postsynaptic potentials (PSPs), action potential after-discharge, and spontaneously occurring PSPs. 2. Broad-spectrum excitatory amino acid (EAA) antagonists, kynurenic acid (KYN) and gamma-d-glutamylglycine (DGG), significantly diminished or eliminated electrically evoked depolarizing PSPs and spike discharges. These compounds also greatly reduced the amplitude and frequency of spontaneous PSPs. 3. The specific N-methyl-D-aspartate (NMDA) receptor antagonist, DL-2-amino-5-phosphonopentanoic acid (AP5), did not significantly reduce these measures of synaptic activation under these experimental conditions. 4. The gamma-aminobutyric acid (GABA) antagonist, bicuculline methiodide (BIC), partially antagonized some PSPs when the cells were hyperpolarized (-75 to -80 mV) with steady injected currents; KYN antagonized BIC-resistant PSPs. 5. The involvement of a hypothetical cholinergic input to the SON in the responses to stimulation of the region dorsolateral to the SON was tested by bath application of nicotinic cholinergic antagonists, particularly d-tubocurarine (dTC). Nicotinic cholinergic antagonists, even after prolonged exposure to high concentrations, did not block the responses of SON cells to dorsolateral stimulation. 6. These findings strongly suggest that EAAs mediate fast excitatory synaptic responses of SON neurons to stimulation of cells and axons in the region dorsolateral to the SON. The blockade of almost all spontaneous EPSPs by broad-spectrum EAA antagonists likewise argues that EAAs are responsible for the majority of ongoing fast excitatory input. These responses appear to involve an interaction with kainate- and/or quisqualate-type EAA receptors.
Dependence of retinogeniculate transmission in cat on NMDA receptors
Authors: Sillito A. M. , Murphy P. C. , Salt T. E. , Moody C. I.
Published: December 2017

1. We have examined the possibility that N-methyl-D-aspartate (NMDA) receptors may be involved in the visual response of relay cells in the cat dorsal lateral geniculate nucleus (dLGN). The selective NMDA receptor antagonists D-2-amino-5-phosphonovalerate (APV) and 3-[(+/-)-2-carboxypiperazin-4-yl]-propyl-1-phosphonic acid (CPP) have been iontophoretically applied to X and Y cells in the dLGN and their effects on the visual response to a light spot flashed within the receptive field center determined. 2. The antagonist effects were assessed at ejection current levels producing a selective blockade of the responses to iontophoretically applied NMDA with respect to those elicited by the non-NMDA receptor agonists quisqualate and kainate. These selective effects were determined in an experimental paradigm where the visual response and responses to NMDA and the non-NMDA receptor agonists were compared in the same test run. The data refer to a total population of 52 cells (28 X, 24 Y). 3. Application of APV abolished or greatly reduced the visual responses of both X and Y cells. The mean percentage reduction in the visual response for the X cells studied was 59 +/- 10% (SE; n = 7) and for the Y cells 66 +/- 8% (SE; n = 11). Both the early onset transient and the sustained component of the visual response to the flashed stimulus were equally affected. 4. The antagonist CPP produced a similar pattern of effect to APV, substantially reducing or abolishing the visual response in both X and Y cells.(ABSTRACT TRUNCATED AT 250 WORDS)