Journal of Neurophysiology

Hore, J.; Flament, D.

doi: N/Apmid: 3746391

Abstract The characteristics of discontinuities and tremor that occurred in elbow flexions during cooling of the lateral cerebellar nuclei were investigated in five Cebus monkeys. Discontinuities in movements appeared as rhythmical oscillations (kinetic tremor) when movements were slow or when movements were made with a constant force that loaded the antagonist. These oscillations had similar properties to cerebellar terminal tremor following movements; e.g., their amplitude and frequency were decreased by addition of mass to the handle and they occurred in the absence of visual feedback. The abnormal initial decrease in velocity that initiated oscillations in flexion movements was associated with abnormally early or large antagonist (triceps) electromyogram (EMG) activity. This abnormal EMG activity did not follow the normal inverse relation between initial velocity and antagonist latency from onset of movement. The initial deflection from the expected trajectory was opposed by a second burst of EMG activity in the agonist (biceps). This second burst was not the continuation of a step of EMG activity because its amplitude was often larger than the amplitude of the first agonist burst. The second agonist burst had the properties of a servo-like response: it occurred when biceps shortening was slowed (but biceps was not stretched), its magnitude was proportional to the magnitude or the deflection in velocity, its latency was 50-80 ms from onset of the abnormal decrease in velocity, and it occurred in the absence of visual feedback. However, this servo-like response was disordered because it did not return the limb accurately to the expected trajectory. The servo-like mechanism was studied further by applying torque pulse perturbations during elbow flexions. When the cerebellar nuclei were cooled, agonist responses to the perturbation were proportional to the size of the velocity deflection, but they were prolonged and onset of antagonist activity was delayed. It is suggested that discontinuities and tremor in movements during cerebellar dysfunction result from the same mechanism: alternation between disordered stretch reflexes and disordered servo-assistance mechanisms, both partly involving transcortical pathways. Copyright © 1986 the American Physiological Society

Mano, N.; Kanazawa, I.; Yamamoto, K.

doi: N/Apmid: 3746392

Abstract Four rhesus monkeys were trained to perform visually guided wrist tracking movements (50). While they performed tasks by wrist flexion or extension from a neutral position, simple-spike (SS) and complex-spike (CS) discharges of a single Purkinje cell (P-cell) were recorded from intermediate and lateral parts of cerebellar hemispheres (lobules IV to VI) ipsilateral to the task-performing wrist. Of approximately 400 P-cells observed, 215 (54%) significantly increased or decreased their SS discharge rate during task performance (task-related P-cells). Of these, 161 were selected for analysis of CS activity; in these P-cells, we could reliably discriminate between CS and background SS by a spike discriminator. The 161 P-cells were further classified into response locked (n = 65) and poorly locked (n = 96) cells according to temporal coupling of the SS frequency modulation to the onset of wrist movements. About 60% of the response-locked P-cells showed a phasic increase (statistical significance level: P less than 0.01) of CS firing rate at the onset of wrist tracking movement. In a few P-cells, a phasic decrease (statistically insignificant) of CS firing rate was observed with the wrist movement. In most P-cells, an increase of CS firing rate was observed with both rapid- and slow-tracking wrist movements. The increase was larger with faster step-tracking movement than with slower ramp-tracking movement. In most P-cells, the CS activity increased with both wrist flexion and extension; in some cells, however, it increased only with either flexion or extension. In most of the response-locked P-cells, the increase of CS firing rate occurred during motor time, i.e., after the onset of the EMG change in prime movers and before the beginning of wrist tracking movement. The increase occurred phasically at the onset and/or at the recovery phase of SS frequency modulation. At neutral wrist position, the maintained frequency of the CS was 0.72 +/- 0.29 CS/s (mean and SD for 161 task-related P-cells). Compared with the frequency at neutral position, the CS frequency did not change tonically during maintained flexed or extended wrist position in any response-locked P-cells. There was no increase of CS firing rate when the monkey returned the handle to center position after completing the tracking task, even in P-cells that had shown a significant increase of CS activity during tracking.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1986 the American Physiological Society

Yokota, T.; Nishikawa, Y.; Koyama, N.

doi: N/Apmid: 3018186

Abstract A population of neurons in the somatosensory part of the nucleus ventralis posteromedialis (VPM proper) that responded to electrical stimulation of the tooth pulp were studied in cats under urethan-chloralose anesthesia. Two classes of units responsive to electrical stimulation of the contralateral canine tooth pulp were identified. One class was responsive only to tooth pulp stimulation and these units were designated as tooth pulp specific (TPS) units. The other class of units responded to mechanical stimulation of the contralateral trigeminal integument in addition to tooth pulp stimulation. Their receptive field characteristics identified them as wide dynamic range (WDR) units responsive to tooth pulp stimulation. Both classes of units were located in the shell region of the caudal VPM proper; TPS units were coexistent with trigeminal nociceptive specific (NS) units and were found in the dorsomedial as well as ventromedial parts of the NS zone. WDR units responsive to electrical stimulation of the tooth pulp were located in the dorsomedial as well as ventromedial parts of WDR zone, a narrow band, approximately 300 micron wide, just in front of the NS zone. Tooth pulp units in the dorsomedial shell region of the VPM proper responded to the maxillary canine tooth pulp, whereas those in the ventromedial shell region responded to the mandibular canine tooth pulp. Some tooth pulp units in these two regions were responsive to stimulation of both maxillary and mandibular canine teeth. Both TPS and WDR units were antidromically excited by electrical stimulation of the SI area of the somatosensory cortex. Cooling the dorsolateral surface of the caudal medulla oblongata reversibly blocked tooth pulp evoked responses of TPS and WDR units. Trigeminal tractotomy just above the level of the obex irreversibly abolished tooth pulp-evoked responses of TPS and WDR units. These findings suggested that TPS neurons in the marginal layer of the trigeminal subnucleus caudalis and WDR neurons in the lateral part of the subnucleus reticularis dorsalis relay afferent impulses derived from the tooth pulp to the shell region of the VPM proper. Copyright © 1986 the American Physiological Society

Shingai, R.; Christensen, B. N.

doi: N/Apmid: 2427666

Abstract External horizontal cells were enzymatically dissociated from intact catfish (Ictalurus punctatus) retina and pipetted onto a small chamber attached to the stage of an inverted phase-contrast microscope. Individual horizontal cells were recognized by their large size and restricted dendritic arborization. Low-resistance (3-12 M omega) patch-type electrodes were used to record intracellular potentials and to pass current across the cell membrane under either current or voltage-clamp conditions. The average resting potential of isolated horizontal cells was -67 V + 6.9 mV (mean +/- SD, n = 40). At the resting potential, the cell membrane appears to be mainly permeable to K. A depolarizing current step evoked an action potential in the cell. The maximum rate of rise of the action potential (dV/dt) in normal physiological solution was 6.5 +/- 1.8 V/s (means +/- SD, n = 24) and was reduced to 1.2 +/- 0.39 V/s (means +/- SD, n = 9) in 1-10 micron tetrodotoxin (TTX) and 3.2 +/- 1.4 V/s (means +/- SD, n = 6) in Ca-free solution. The maximum dV/dt was reduced in 10 mM extracellular K concentration Ko to about half of that seen in standard saline, and values in 30 or 80 mM Ko were similar to that measured in TTX. Following an action potential, the membrane potential reached a plateau potential of + 17.4 +/- 8.1 mV (means +/- SD, n = 17) and remained depolarized for variable periods of time lasting from less than a second to a few minutes. When the plateau potential was long lasting, the cell repolarized slowly and upon reaching zero rapidly repolarized to the original resting potential. The duration of the plateau potential decreased or was absent in saline containing one of the following calcium channel antagonists: La, Cd, Co, or Ni. The voltage-clamp technique was used to identify the membrane currents responsible for the membrane potential changes seen under current clamp. Experiments were carried out using either a single or two individual electrodes. Fast and steady-state inward currents were recorded from isolated horizontal cells in the voltage range between -20 and +20 mV. These currents were a result of increased membrane conductance to both Na and Ca ions. The Na channels are inactivated at depolarized potentials and are TTX sensitive. Ca channels are partially inactivated at depolarized potentials. The Ca conductance is decreased by Cd, Co, Ni, and La. Ba can substitute for Ca in the channel.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1986 the American Physiological Society

Looft, F. J.

doi: N/Apmid: 3746397

Abstract Cat hairy skin type I, type II, and field mechanoreceptor response characteristics were studied by drawing punctate and grating stimuli across a unit's receptive field (RF). Area RF maps were generated with scans covering approximately 1 X 1 cm using different vertical loadings, scan velocities, and scan orientations. The results from stimulating with a 1 g mass, 1 mm diam, rounded-tip punctate probe indicate that type I units display essentially invariant response topographies as a function of stimulus parameters. Type II units, presumably because of their unidirectional stretch sensitivity, showed response differences that were a function of the scan orientation. Field units, although not considered to be important for stimulus feature extraction, also displayed a directionally sensitive response profile. Changing the vertical loading or the scanning velocity of the stimulus had a minimal affect on the resulting RF profiles for any of the units studied. Grating stimuli with periods of 0.25-2.0 mm were scanned over receptors to study their grating discrimination ability. Different scan directions were used to study the directional sensitivity of a unit. Both type I and II units had optimal scan orientations for minimum grating period discrimination. For type I units, the dome orientation pattern and interdome sensitivities seemed to be a factor in determining the scan direction for minimum grating period detection. For type II units it was equivocal whether scanning parallel or orthogonal to the direction of maximum stretch sensitivity was better for grating detection. Grating response results were qualitatively similar to the results reported by others for receptors in the glabrous skin of primates. Both type I and II units could reliably discriminate gratings with periods of 0.75 mm and could marginally discriminate gratings with 0.5-mm periods. Field units were not well represented in this study, but those units that were studied were unable to unambiguously discriminate a 2.0-mm period grating, the largest one used. Copyright © 1986 the American Physiological Society

Ohzawa, I.; Freeman, R. D.

doi: N/Apmid: 3746398

Abstract We have studied the manner by which inputs from the two eyes are combined in simple cells of the cat's visual cortex. The stimuli for this study are drifting sinusoidal gratings, shown dichoptically at optimal spatial frequency and orientation. The relative spatial phase (disparity) between the gratings for left and right eyes is varied over 360 degrees. Most simple cells show phase-specific binocular interaction such that response amplitudes and phases vary depending on the relative spatial phase. At one phase, response is greater than either of the monocular responses and often greater than the sum of the two. At the phase 180 degrees away from the optimal, the cell's responses are strongly inhibited and often completely suppressed. Phase-specific binocular interaction disappears when the gratings presented to one eye are made orthogonal to the optimal orientation. The degree of binocular interaction does not depend critically on the ocular dominance of the cells. Simple cells that are nearly equally dominated by each eye always exhibit strong phase-specific interaction. The majority of cells that are strongly dominated by one eye, and even those that appear monocular, show phase-dependent changes in responses. We examined the extent of binocular interaction for cells with preferred orientations near vertical compared with those tuned to other optimal orientations. If these cells are conveying information about depth, one might expect a greater degree of binocular phase-specificity for units preferring nearly vertical orientations, which would then be processing horizontal disparities. We find no evidence for this. Predictions of simple-cell responses are derived from a linear model of binocular convergence in which light-evoked neural signals from each eye are summed linearly to determine cell responses. Data from cells generally follow the prediction of the model for both response amplitude and phase. Deviations from predictions of the linear model are found for a minority of cells. This deviation may be accounted for by a threshold mechanism that comes into play after the linear binocular summation. A small proportion of simple cells that appear monocular by alternate tests of each eye show a purely inhibitory influence from the silent eye. This inhibition is not generally dependent on the relative phase of the gratings. We conclude that most binocular interaction in striate simple cells may be accounted for by linear summation of neural signals from each eye.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1986 the American Physiological Society

Hals, G.; Christensen, B. N.; O'Dell, T.; Christensen, M.; Shingai, R.

doi: N/Apmid: 3746395

Abstract Horizontal cells isolated from the catfish retina were exposed to radiolabeled glutamate, glycine, gamma-aminobutyric acid (GABA), and sucrose to determine if the enzymatic dissociation procedure altered the high-affinity uptake mechanism for GABA and generally reduced membrane selectivity. As in the intact retina, isolated cells could transport GABA but not the other substances. The horizontal cells were voltage clamped using a single low-resistance patch-type electrode. The acidic amino acid L-glutamate, and its analogues kainate and quisqualate, were applied to the cell by pressure ejection from a nearby pipette. All three agonists produced inward currents that reversed near O mV. Quisqualate produced a current with a similar time course as glutamate, but the time course of the response to kainate was faster. The agonists N-methyl-D-aspartate and L-aspartate had little effect on the membrane conductance. The current-to-voltage (I-V) relationship for all three agonists was nonlinear when the membrane potential was hyperpolarized. The nonlinearity was, at least in part, a result of the decreased response to the three agonists. Removal of Mg did not alter this nonlinear relationship. When the inward potassium rectifier was blocked with 100 microM Ba, the response to glutamate was increased compared with the control experiment before block by barium; however, the I-V relationship was still highly nonlinear. Thus glutamate block of the inward potassium current cannot account entirely for the nonlinear I-V. The increase in membrane permeability to specific ions in the presence of an agonist was determined by ion substitution experiments and measuring the shift in the reversal potential. The three agonists appear to increase the membrane permeability to cations but not to anions. The amino acid antagonists cis-2,3-piperidine dicarboxylic acid (PDA) and D-glutamyl glycine (DGG) were bath applied to test their ability to block the depolarizing effects of glutamate. DGG had no measureable effect at 100 microM concentration, whereas PDA reversibly reduced the glutamate response at 1 mM concentration although block was incomplete. Isolated horizontal cells responded to bath-applied glutamate in concentrations of 10-500 microM. In concentrations of glutamate greater than 50 microM, when the membrane potential was held at the resting potential, the inward current reached a maximum followed by a decrease to a steady-state level. This apparent time-dependent desensitization at high agonist concentrations was at least partially removed when Mg was removed from the bathing solution.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1986 the American Physiological Society

Ohzawa, I.; Freeman, R. D.

doi: N/Apmid: 3746399

Abstract We have studied the manner by which inputs from the two eyes are combined in complex cells of the cat's visual cortex. The stimuli are drifting sinusoidal gratings presented dichoptically at optimal spatial frequency and orientation. The relative phase between the gratings for left and right eyes is varied over 360 degrees. Approximately 40% of complex cells show phase-specific binocular interaction where response amplitudes vary depending on the relative phase of the gratings shown to the two eyes. This interaction is similar to that observed for most simple cells. We devised a test to examine whether the phase-specific interaction in complex cells results from linear convergence of neural signals at subunits of the receptive fields. The data from this test are consistent with a linear combination model. The phase-specific binocular interaction data from complex cells imply that the optimal relative phase of the receptive field subunits is closely matched. Another type of complex cell, approximately 40% of the total, could be driven through either eye, but exhibited non-phase-specific responses to dichoptically presented gratings. This type of interaction is found only in complex cells. Binocularly non-phase-specific complex cells may have subunits whose optimal relative phases are random or monocular. The division of complex cells into these two major groups (binocularly phase specific and non-phase specific) is independent of whether they are standard or special complex-cell types. A small proportion (8%) of complex cells that appear monocular by alternate tests of each eye show a purely inhibitory influence from the silent eye. This inhibition is not generally dependent on the relative phase of the gratings. Unlike simple cells, complex cells are not a homogeneous group. However, nearly half of complex cells show phase-specific binocular interaction that is probably the result of linear convergence. Combined with the results from simple cells, the majority of binocular interaction in the striate cortex may be accounted for by linear summation of neural signals from each eye. This provides a simplified view of the nature of binocular interaction in the visual cortex. Copyright © 1986 the American Physiological Society

Meredith, M. A.; Goldberg, S. J.

doi: N/Apmid: 3746400

Abstract Conjugate eye movements in the horizontal plane are accomplished by the coactivation of the medial rectus (MR) muscle of one orbit and the lateral rectus (LR) muscle of the other. While control of these excursions has been thought to be effected by identical inputs to these muscles, recent studies have demonstrated that MR motoneurons receive different inputs than LR motoneurons. This raises the question of whether the character of the muscles they control are different. The present study evaluated the contractile properties of MR and LR muscle units in the cat. Based on the mechanical aspects of their contractile properties, only two physiological types of muscle units were identified within the MR and LR muscles: twitch and non-twitch muscle units. Twitch muscle units represented over 90% of the units sampled in each muscle. Significant differences in the rate-related and the tension-related contractile properties were demonstrated between MR and LR twitch muscle units. MR muscle units exhibited significantly faster twitch contractions than did LR units. The rate of stimulation at which MR units exhibited fused tetany was significantly higher than for LR units, although units from both muscles demonstrated similar rates of rise of tension at fusion. The rate of rise of tension was closely correlated to tension production (twitch and tetanus) in each muscle. However, MR muscle units demonstrated significantly weaker maximum tetanic tensions and lower tetanus-to-twitch ratios than LR units. These data indicate that while similar physiological types of muscle fibers are present within the MR and LR, MR muscle units are adapted for faster rate-related properties, whereas LR units are adapted for greater tetanic tensions. These distinctions between MR and LR muscle units, coupled with differences between the afferent inputs to their respective motoneurons, suggest that the preservation of conjugacy during horizontal gaze shifts may require a complex interaction of peripheral and central factors. Copyright © 1986 the American Physiological Society

Carter, M. C.; Smith, J. L.

doi: N/Apmid: 3746394

Abstract The simultaneous control of the hindlimb paw-shake response and hindlimb walking at slow treadmill speeds (0.2-0.4 m/s) was examined in adult cats spinalized at the T12 level, 3-6 mo earlier. Paw shaking was elicited by either 1) application of adhesive tape or 2) water to the right hindpaw. To assess intralimb and interlimb coordination of the combined behaviors, activity from selected flexor and extensor muscles at the hip, knee, and ankle was recorded, and the kinematics of these joints were determined from high-speed cinefilm. When paw shaking was combined with hindlimb walking, the response in the stimulated limb was initiated during swing (F phase) of the step cycle. The onset of knee extensor activity provided the transition from the flexor synergy of swing to the mixed synergy of paw shake. At the end of the paw shake, an extensor synergy initiated the E-1 phase of swing, and the resultant joint motion was in-phase extension at the hip, knee, and ankle to lower the paw for contact with the treadmill belt. During the rapid (81 ms) paw-shake cycles, knee extensor and ankle flexor muscles exhibited single, coactive bursts that were reciprocal with coactive hip and ankle extensor bursts. This mixed synergy was reflected in the limb coordination, as knee flexion coincided with ankle extension and knee flexion coincided with ankle extension. Phasing of hip motions was variable, reflecting the role of the proximal in stabilization during paw shake (16). Although the number of paw-shake cycles combined during swing varied greatly from 2 to 14, average cycle periods, burst durations, and intralimb synergies were similar to those previously reported for spinal cats tested under conditions in which the trunk was suspended and hindlimbs were pendent (23, 27). For step cycles during which a long paw-shake response of 8-14 cycles occurred, swing duration of the shaking limb increased by 1 s, and during this prolonged interval, the contralateral hindlimb completed two support steps. Stance duration of the support steps was also prolonged. This adjustment maximized the duration of paw-contact and minimized any period of nonsupport by the contralateral hindlimb during paw shake. Completion of the paw-shake response was followed by either an alternating, or a nonalternating, gait pattern on the recovery steps. One spinal cat combined locomotion with short two-cycle paw-shake responses, and because the shortened response was limited primarily to the time ordinarily devoted to swing, interlimb adjustments were slight.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1986 the American Physiological Society