Journal of Neurophysiology

Hayashida, Y.; Koyano, H.; Eyzaguirre, C.

doi: N/Apmid: 7452324

Abstract 1. The carotid body and its nerve, removed from anesthetized cats, were placed in physiological saline flowing under paraffin oil. The nerve, lifted into the oil, was used for either electrical stimulation or recording of the total afferent discharge. Intracellular recordings were obtained from individual nerve fibers and endings within the carotid body. The recording sites were identified by injecting Procion yellow through the intracellular electrodes; the tissues were then prepared for histology and observed with episcopic fluorescence or Nomarski optics. 2. Intracellularly recorded chemosensory fibers conducted at 1.1-30 m/s and usually displayed action potentials of regular amplitude. At times, however, some spikes become partially blocked while others maintained their original amplitude. "Natural" (hypoxia) or chemical (ACh or NaCN) stimulation induced different patterns of frequency changes of the large and small action potentials. This indicated nerve fiber branching at some distance from the recording site. 3. Intra- and extracellularly recorded spikes were blocked in 0 Na+0 by tetrodotoxin (TTX) or procaine. 4. During chemical stimulation, a slowly occurring depolarization (receptor or generator potential) was recorded intracellularly from the afferent fibers. It developed concomitantly with the increase in discharge. 5. Impalement of single nerve terminals (histologically identified) showed numerous "spontaneous" depolarizing potentials (SDPs) that had a mean amplitude of 5.6 mV, a mean duration of 46.1 ms, and nearly random distribution. They increased in frequency and summated during chemical stimulation. SDPs originated from either the site of recording or from neighboring areas. When the SDPs attained a certain amplitude, they seemed to give rise to action potentials. Also, relatively well developed or partially blocked spikes (apparently originating elsewhere) were recorded from single nerve terminals. 6. The receptor (generator) potential of chemosensory receptors appears to be an integrated response formed by multiple activity originating in different nerve endings. Copyright © 1980 the American Physiological Society

Adams, W. B.; Parnas, I.; Levitan, I. B.

doi: N/Apmid: 6256509

Abstract 1. Long-lasting inhibition is a synaptically mediated response found in certain molluscan nerve cells that fire action potentials in bursts. It is elicited by repetitive stimulation of a presynaptic nerve and may last for minutes or hours after stimulation. 2. Voltage-clamp techniques were employed to measure the voltage dependence of the synaptically elicited current. Current-voltage curves were obtained by stepping or sweeping the voltage over the range -40 to -120 mV. 3. Long-lasting inhibition was found to be mediated by two separate conductance mechanisms. A component that reverses near -80 mV is most prominent at times up to 5 min following stimulation. A component with no reversal potential between -40 and -120 mV predominates at later times. 4. The reversible component is attenuated by reducing the intensity of stimulation of the presynaptic nerve, by injection of TEA into the postsynaptic cell, or by activation of a potassium conductance with serotonin prior to stimulation of the nerve. Thus, the reversible component appears to be mediated by an increase in potassium conductance. 5. The effects of the nonreversible component measured in the soma appear to be too large to attribute it to a conductance change that is electrically "distant" from the soma. It is attenuated by turning off a resting inward ion conductance with dopamine prior to stimulation of the nerve. It is not affected by short exposure to ouabain, but is attenuated by longer exposures that reduce the sodium and calcium gradients. Thus, the nonreversible component may be mediated by a decrease in voltage-dependent inward current flow carried by sodium or calcium. Copyright © 1980 the American Physiological Society

Bidaut, M.

doi: N/Apmid: 6256507

Abstract 1. Picrotoxin (PTX) (10(-7)-10(-6) M) completely blocked most inhibitory synapses in the pyloric pattern generator of the lobster (Panulirus interruptus) stomatogastric ganglion. The sensitivity of synapses from most classes of identified neurons was examined. Blockade was at least partly reversible with prolonged washing. 2. The synapses from pyloric dilator (PD) neurons were the only inhibitory synapses that picrotoxin failed to block completely. 3. A correlation is derived that brief, fast-rise inhibitory postsynaptic potentials (IPSPs) are picrotoxin sensitive, whereas a slow rounded component of IPSPs from PD neurons is not picrotoxin sensitive. 4. Picrotoxin caused specific changes in the pattern of the motor rhythm produced by the 16-cell pyloric network. This sheds some light on the functional role of particular synapses in the pyloric generator. 5. The endogenously bursting neurons (PD and anterior burster (AB)), which drive the pyloric rhythm, kept a similar burst rate. 6. Under picrotoxin, the pyloric "follower" neurons all moved to later phase relative to the "driver" group. Some normally antagonistic cells, related by reciprocal inhibitor connections, became in-phase. These and other pattern changes could be related to blockade of particular synapses. 7. The pyloric rhythm was still quite recognizable under picrotoxin despite the drastically altered circuitry of the synaptic network. This supports the idea that periodic inhibition from the PD driver neurons plays a primary role in creating the pyloric pattern. Copyright © 1980 the American Physiological Society

Tapper, D. N.; Wiesenfeld, Z.

doi: N/Apmid: 7452326

Abstract 1. We have studied some properties of a sacral dorsal spinal gray matter network. the lamina 4:type 1 afferent fiber network (L4:T1 network) in 24 adult cats that were anesthetized with urethan and the spinal cord transected at the thoracolumbar junction. 2. The network in the first sacral segment is composed of a subgroup of lamina 4 cells as principal neurons that are connected to type 1 afferent fibers emerging from the skin, the manipulable input channels. Other primary afferent fibers and axons of central cells of other segments may also be input elements. Cells of the substantia gelatinosa (SG) and of the marginal layer constitute the intrinsic neurons. We monitored the output of the network by unit recording of the lamina 4 cell's impulse activity. 3. We activated the network by single impulses delivered via single type 1 afferent fibers. We stimulated fibers individually by focused electrical stimulation and monitored the selectivity of the stimulus by a computer-averaging procedure. The basic stimulus paradigm (each stimulus trial) consisted of 100 single impulses delivered 1 impulse/3 s. For nine networks, each of the accessible type 1 fibers was used as an input channel. 4. The typical pattern of response to the 100 impulses was composed of: a) an early discharge lasting for 5 ms after the input impulse invades the central arbor of the type 1 fiber, b) a late discharge of variable duration terminated by c) a postresponse reduction in ongoing discharge rate. Early-only and late-only discharges were occasionally observed. We conclude that the response pattern reflects the specific neuronal and synaptic configuration that is engaged by each input channel. 5. Across input channels, the early discharge was characterized by: a) a bimodal distribution of low- and high-probability responses, reflecting two predominating groups of type 1 input channels, one believed to be weakly coupled and the other strongly coupled to the principal neuron; b) relatively little multiple discharge; c) modal response during the first 2 ms of the discharge; d) response produced via a monosynaptic connection of the type 1 fiber with the lamina 4 neuron and average synaptic delay of 0.53 +/- 0.01 ms (mean +/- SE, n = 100); e) in general, a stable response throughout the 5-min stimulus trial, although an occasional habituating response was noted. 6. The late discharge was characterized by: a) a multiple discharge and a wide response jitter; b) mean duration approximately 29 ms; c) in general, high-probability response; d) a tendency for the response to wane during the course of the stimulus trial. 7. We observed no relationship between the magnitude of the early or late response and the level of ongoing discharge when considered across input channels. However, for a given input channel over time, the output response was often highly correlated with the level of ongoing discharge. The effect was best described by a log-log relationship... Copyright © 1980 the American Physiological Society

Optican, L. M.; Robinson, D. A.

doi: N/Apmid: 7452323

Abstract 1. The ability of the central nervous system to compensate for saccadic dysmetria was demonstrated in rhesus monkeys. The behavior of this adaptive mechanism after cerebellar ablations was examined. 2. Monkeys were trained to fixate small target lights. Eye movements were monitored while the animals were seated, with their heads fixed, in a rotating magnetic field. The horizontal recti muscles of one eye were weakened by tenectomy. Saccades made by this weakened eye were hypometric and followed by postsaccadic drift. 3. When the patch was switched so that the weak eye was viewing, the hypometric saccades made by the weak eye gradually became larger, until after 3 days they were essentially orthometric. This indicated that the central nervous system could compensate for a peripheral weakness. 4. The tenectomy operation reduced the strength of the muscles, creating hypometria, and upset the ratio of viscosity to elasticity in the orbit, creating postsaccadic drift in the weak eye. The innervation required to make a saccade has both phasic and tonic components, the so-called pulse and step. The sacccadic repair mechanism increased both the pulse and the step to compensate for the hypometria and also adjusted the ratio of the pulse to the step to eliminate postsaccadic drift. 5. Total cerebellectomies were performed on two monkeys, each of which had one tenectomized eye. These ablations created an enduring saccadic hypermetria and postsaccadic drift in the unoperated eye of both animals. The total cerebellectomy abolished all adaptive repair of the saccadic system. 6. Partial cerebellectomies were performed on two monkeys, each of which had one tenectomized eye. Lesions of the vermis and paravermis (lobes IV-IX) and the fastigial nuclei created an enduring saccadic hypermetria without postsaccadic drift in the unoperated eye of both animals. These lesions abolished adaptive control of the pulse of innervation. Adaptive changes in the step of innervation still occurred, so that postsaccadic drift was always eliminated in the experienced, viewing eye. Thus the midline cerebellum (vermis, paravermis, and fastigial nuclei) appears to be important for repair of saccadic dysmetria, but not for repair of postsaccadic drift. Additional evidence that postsaccadic retinal slip cannot be compensated for in flocculectomized monkeys suggest that the adaptive control of the step may depend on the flocculus. 7. After cerebellar lesions the monkeys were able to make saccades of all amplitudes and directions. The principal deficit in these animals seemed to be that the pulse and step of innervation were no longer appropriate to the target displacement. We conclude that the cerebellum's principal contribution to saccadic eye movements is the adjustment of the gains of the pulse- and step-generating mechanisms. Hence this study supports the hypothesis that repair of dysmetria is a general function of the cerebellum. Copyright © 1980 the American Physiological Society

Terzis, J. K.; Dykes, R. W.

doi: N/Apmid: 7452327

Abstract 1. A total of 758 fibers were isolated from previously transected and repaired ulnar nerves of five baboons. These fibers were compared to fibers from normal and previously crushed nerves studied in an earlier experiment. 2. The conduction velocities of the proximal portion of the injured axons dropped below normal, and this reduction persisted until reinnervation appeared nearly complete. 3. The receptive-field organization and response characteristics of 79 cutaneous afferent fibers serving the glabrous skin were studied in detail and compared to cutaneous afferent fibers of normal and previously crushed nerves studied earlier. 4. Initially, receptive fields were small and irregular, and often one fiber served several distinct skin regions. Ten months later, most of these abnormalities were no longer apparent. 5. Thresholds for single impulses elicited by von Frey hairs remained elevated for up to 4 mo after the receptive field reappeared, but then dropped abruptly to a near-normal range. 6. After reinnervation, rapidly adapting fibers displayed tuning curves characteristic of their submodality, but thresholds were elevated and only began to approach the normal range 6 mo after reinnervation. 7. After reinnervation, slowly adapting fibers displayed stimulus-response curves with elevated thresholds and they tended to saturate at lower stimulus intensities than normal fibers. 8. When compared to the return of function following a crushing injury, axons that had been transected displayed a slower time course for the return to normal values of conduction velocity and threshold. Receptive-field organization also remained abnormal for a longer time period. 9. These data support the hypotheses that a) breaking the continuity of the Schwann cells and extracellular matrix that occurs during transection but not during crush is a major factor leading to errors of axonal regeneration in the distal stump, b) submodality specificity is a property of the regenerating axon, and c) regenerating axons are influenced by an internal or external cue, causing them to form and maintain a single relatively homogeneous receptive field. Copyright © 1980 the American Physiological Society

Selverston, A. I.; Miller, J. P.

doi: N/Apmid: 6256508

Abstract 1. Four factors contribute to pattern generation in the pyloric network of the lobster stomatogastric ganglion. These are: a) endogenously oscillating neurons; b) synaptic network properties; c) nonlinear cellular properties, including the generation of plateau potentials; and d) excitatory input from the commissural ganglia. The roles and relative importance of these factors were investigated with a new technique for inactivating single specific identified neurons. 2. In stomatogastric ganglia in which the excitatory input is left intact, a) pattern generation continues when any cell or pair of cells other than the endogenous bursters are inactivated, b) pattern generation also continues when the endogenous bursters are inactivated, c) pattern generation ceases when the endogenous bursters plus one other particular cell are inactivated. This cell, although not an endogenous burster, displays a strong tendency to generate plateau potentials. 3. In stomatogastric ganglia that have been isolated from excitatory input, a) pattern generation continues when any cell or pair of cells other than the endogenous bursters are inactivated, b) pattern generation ceases when the endogenous bursters are inactivated. 4. Some of the inputs to the stomatogastric ganglion normally fire in bursts. However, their potentiation and acceleration of the output pattern are also produced by tonic stimulation of the nerve. The effect of one of those inputs is mimicked by bath application of dopamine to the stomatogastric ganglion. 5. The roles and importance of the three most important factors were qualitatively summarized in a chart specifying the activity of the network as a function of its intactness. Copyright © 1980 the American Physiological Society

Wolpaw, J. R.

doi: N/Apmid: 6450275

Abstract 1. Monkeys were trained to maintain hand position against a range of constant forces. Short-latency responses to passive wrist extension or flexion, as well as short-latency responses to stretch of a single wrist muscle, were recorded from units in areas 4, 3, 1, and 2. These responses were compared to unit activity during active holding and during active movement. 2. Units related to active holding and to active movement were most common in areas 4 and 2. Three-quarters of these units displayed a specific correlation between their passive and active behaviors. Thus, a unit excited by passive extension was excited during active holding against extension force and excited during an active flexion movement. This behavior is similar to the expected concurrent behavior of muscle stretch receptors. By demonstrating that a significant number of task-related units give qualitatively similar responses to passive extension and passive flexion, the results appear to explain the disagreement among previous studies (5, 9, 36) in regard to area 4 behavior during active and passive movements. 3. Area 4 units responded similarly to passive wrist extension and electromagnetic stretch of a single flexor muscle occurring in the absence of wrist extension, indicating that muscle stretch was important in determining area 4 unit responses to passive movements. 4. The similarity of area 4 behavior to area 2 behavior in active and passive situations, along with the observation that area 2 responses to passive movements occurred several milliseconds earlier than those of area 4, emphasizes the importance of area 2 in motor performance and is consistent with significant area 2 mediation of area 4 responses. 5. Results support the hypothesis of an oligosynaptic transcortical pathway (22, 32, 34), beginning in large part with muscle stretch receptors. Furthermore, the correlation noted between short-latency responses to passive movement and task-related activity suggests that this transcortical pathway not only mediates responses to passive movement but may be responsible, to a significant degree, for task-related activity during undisturbed performance. Thus, active position maintenance and active movement were probably accomplished, at least in part, by increasing and decreasing the influence of this pathway on specific area 4 neurons and thereby producing the patterns of area 4 activity responsible for task performance. Copyright © 1980 the American Physiological Society

Kelly, J. B.

doi: N/Apmid: 6778973

Abstract 1. Studies with cats, dogs, and monkeys have shown that bilateral ablation of auditory cortex can result in severe deficits in the ability to localize sounds in space. In the present series of studies we sought to extend this observation to include the laboratory rat. 2. Rats were tested in a two-choice sound-localization task, which required a spatial response to a distant goal box. Although the test conditions were very similar to those employed with cat, dog, and monkey, deficits following cortical ablation were minimal. Indeed, following bilateral ablation of both primary and secondary auditory projection areas, rats were still capable of localization at small angles. 3. Several possibilities were considered to explain the apparent species difference in the effect of cortical ablations. It seemed unlikely that the difference was due simply to testing procedures or details of stimulus presentation. Central nervous system factors were discussed, including the possibility that the degree of impairment was related to the extent of cortical development in different species. It was concluded that the effects of auditory cortical ablation are not the same for all mammals and that for some species auditory cortex is not essential for sound localization. Copyright © 1980 the American Physiological Society

Rivot, J. P.; Chaouch, A.; Besson, J. M.

doi: N/Apmid: 7452322

Abstract 1. In the rat under N2O-halothane anesthesia, stimulation of the nucleus raphe magnus (NRM) with stimulus parameters similar to those used to obtain analgesia in freely moving animals strongly inhibits the responses of dorsal horn convergent neurons due to A-delta- and C-afferents. 2. Responses to noxious radiant heat were also depressed, and pronounced post-effects were frequently observed. 3. Comparison between coupled sites of stimulation in NRM and in adjacent bulbar reticular formation (BRF) on responses to C-fibers revealed the preeminent effects of NRM; these were systematically encountered (93% of neurons), much more pronounced, and of longer duration. 4. The latency of these inhibitory effects (around 20 ms) suggests the participation of myelinated axons in such descending action and, consequently, we question the involvement of unmyelinated serotonergic fibers. 5. However, descending inhibitory influences from NRM on responses to C-fibers are reduced after 5-hydroxytryptamine (5-HT) depletion by p-chlorophenylalinine (pCPA), thus demonstrating the implication of both serotonergic and nonserotonergic pathways. 6. In addition, after pCPA pretreatment, long-lasting and sustained excitatory effects from NRM were observed in 35% of convergent neurons; their possible origin is discussed. Copyright © 1980 the American Physiological Society