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PubMed1980

Activity of neurons of cerebellar nuclei during fictitious scratch reflex in the cat. II. Interpositus and lateral nuclei.

The activity of neurons of the interpositus and lateral cerebellar nuclei was recorded during fictitious scratch reflex in thalamic cats immobilized with Flaxedil. Interpositus neurons were identified by antidromic response to stimulation of the contralateral red nucleus. The interpositus neurons responding to passive movements of the ipsilateral hindlimb manifested rhythmical modulation of the discharge in relation with the scratch cycle. The neurons generated bursts of impulses separated by periods of silence. Different neurons were active in different parts of the scratch cycle, but most of them were active in the second half of the flexor phase. When the scratch reflex was evoked on the contralateral side, rhythmical modulation was observed in about half of the neurons, and it was less pronounced than in the case of ipsilateral scratching. Rhythmical modulation of cerebellar neurons during fictitious scratching is determined by signals coming from the central spinal mechanism, generating rhythmical oscillations, via the ventral spinocerebellar tract (VSCT) and the spinoreticulocerebellar pathway (SRCP). Results of separate transections of these pathways showed that the VSCT plays the crucial role in modulating interpositus neurons. Neurons of the lateral nucleus exhibited no modulation during fictitious scratching.

Afferent Pathways↗
PubMed1980

Motoneuron membrane changes associated with spinal shock and the Schiff-Sherrington phenomenon.

Following transection of the thoracic spinal cord, in a decerebrate cat, the forelimbs exhibit an enhanced extensor stretch reflex while the ipsilateral flexion reflex is more difficult to elicit (Schiff-Sherrington Phenomenon). The hindlimbs on the other hand have an increased threshold for the extensor stretch reflex while flexion reflexes are hyperactive (spinal shock). This investigation was designed to examine the synaptic events mediating the Schiff-Sherrington Phenomenon (SSP) and spinal shock; and to characterize any differences in the response of flexor and extensors alpha-motoneurons. This was accomplished by measuring membrane potential and input resistance of identified forelimb and hindlimb alpha-motoneurons before, during, and after coldblock of the low thoracic cord. During post-brachial spinal cord coldblock, forelimb extensor motoneurons depolarized while flexor motoneurons hyperpolarized. Both flexor and extensor motoneurons in the lumbar cord hyperpolarized. These observations account at least in part for the behavioral manifestation of increased extensor tone seen during the SSP and for the reflex depression seen during spinal shock. The membrane potential changes observed in this study were mediated through a direct effect on alpha-motoneurons since these animals were flaxedilized and gamma loop activity was probably negligible. The hyperpolarization of hindlimb motoneurons was apparently due to the removal of descending facilitation, while the depolarization seen in forelimb extensor motoneurons appeared to be due to a release of facilitation. The mechanism of the hyperpolarization observed in some forelimb motoneurons was unclear.

Animals↗
PubMed1982

Cardiovascular responses elicited by electrical stimulation of the amygdala central nucleus in the rabbit.

Recent behavioral and anatomical evidence suggests the involvement of the amygdala central nucleus projection to medullary cardioregulatory nuclei in the expression of conditioned bradycardia during aversive Pavlovian conditioning in the rabbit 6,7,11,15. The present study sought to determine the extent to which electrical stimulation of the central nucleus produces bradycardia in the rabbit, and the extent to which any bradycardia elicited varies with stimulation at sites within as opposed to adjacent to the medial component of the central nucleus, the component from which the projection to cardioregulatory nuclei originates. Over 900 sites in 30 rabbits anesthetized with alpha-chloralose were explored. Monopolar stimulation (30-100 Hz; 0.5 ms pulse duration; 5.0 s train duration; 100-500 microamperemeter) at sites within the central nucleus produced bradycardia and depressor responses. Maximum bradycardia was produced from sites within the anterior, medial component of the nucleus. This response usually began within one second of stimulus onset, reached peak magnitude within two seconds of stimulus onset and in many instances was followed by a slight tachycardia following stimulus termination. The accompanying depressor responses occurred at longer latencies than the bradycardia responses. The responses persisted following artificial ventilation and immobilization by Flaxedil and were attenuated by i.v. injections of atropine methylnitrate. While bradycardia and depressor responses were elicited from sites immediately dorsal, ventral and lateral to the medial central nucleus, component. The results are consistent with previous evidence which suggests a contribution for the central nucleus in the expression of cardiovascular responding during aversive Pavlovian conditioning in the rabbit.

Amygdala↗
PubMed1984

Activity of cerebellar Purkinje cells during fictitious scratch reflex in the cat.

The activity of Purkinje cells (PCs) was recorded in the anterior lobe (the vermis and pars intermedia) and in the paramedian lobule of the cerebellum during the fictitious scratch reflex in thalamic cats immobilized with Flaxedil. In the anterior lobe, the activity of many PCs was rhythmically modulated in relation to the scratch cycle: they generated bursts of impulses separated by periods of silence. Different PCs were active in different phases of the scratch cycle. In many cases the discharge modulation was irregular: the burst duration and the discharge rate in the burst varied considerably in subsequent cycles. The rhythmical activity of PCs was determined by modulation of the frequency of 'simple spikes' reflecting the mossy fiber input. Generation of 'complex spikes' reflecting the climbing fiber input in most PCs was not related with the scratch rhythm. In the paramedian lobule, rhythmical modulation of PCs was practically absent. Rhythmical modulation of PCs in immobilized cats is determined by signals coming from the central spinal mechanism of scratching via the ventral spinocerebellar tract (VSCT) and the spinoreticulocerebellar pathway (SRCP). Results of separate transections of these pathways demonstrated that the VSCT plays the crucial role in modulating the PCs.

Afferent Pathways↗
PubMed1988

The inhibitory effect of somatic inputs on the excitatory responses of vagal cardiomotor neurones to stimulation of the nucleus tractus solitarius in rabbits.

Experiments were done in 41 rabbits anaesthetized with urethane and chloralose, paralyzed with Flaxedil and ventilated artificially. Extracellular recordings of 142 units were made in the dorsal vagal nucleus (DVN) and the nucleus ambiguus (NA), identified by antidromic response to stimulation of the cervical vagus nerve. In total 63.5% of them exhibited spontaneous activity and 22 units (17 in DVN and 5 in NA) showed a cardiac rhythm; their antidromic conduction velocity was 3.7-12.5 m/s, which suggests their having axons in the range of B fibres. These neurones were classified as vagal cardiomotor neurones. A total of 16 DVN and 4 NA vagal cardiomotor neurones were excited orthodromically by electrical stimulation of the contralateral nucleus tractus solitarius (NTS). Electrical stimulation of the superficial peroneal nerve (SP) with low intensity or the deep peroneal nerve (DP) with high intensity which activated C fibres inhibited excitatory responses of 16 neurones (14 in DVN and 2 in NA). The other 4 neurones were unaffected by SP inputs. These results provide electrophysiological evidence for the inhibitory effect of somatic inputs on the evoked discharges of vagal cardiomotor neurones in the DVN and the NA.

Animals↗
PubMed1988

Taste responses in the nucleus tractus solitarius of the chronic decerebrate rat.

The ingestive behavior of decerebrate rats has been studied for some time, yet little is known of its neural substrates. While taste fibers in rats proceed from hindbrain to thalamus and ventral forebrain, these regions return centrifugal fibers to the hindbrain by which lower-order taste activity may be influenced. We examined the functional characteristics of taste neurons in the nucleus tractus solitarii (NTS) of chronic decerebrate rats in which this reciprocal communication was disrupted and compared them with those of intact controls. Nine Wistar rats were decerebrated at the supracollicular level. After a minimum of one week recovery, they were immobilized with Flaxedil, anesthetized locally and prepared for recording. The responses of 50 taste cells were isolated bilaterally from the NTS of these animals, while the activity of 50 additional neurons was recorded from 12 intact rats under the same conditions. Taste stimuli included 7 Na-Li salts, 3 sugars, HCl and citric acids, quinine HCl and NaSaccharin. Mean spontaneous activity in decerebrates was 6.5 spikes/s, 36.0% lower than the level in intact animals. Mean evoked activity was reduced by 32.6%. Analyses of the effects of stimulus quality, intensity and time course of the responses all indicated that the decrease in activity was attributable to the inability of taste cells in decerebrate rats to respond to demands for high discharge rates. This deficit could be responsible for the failure of these animals to develop conditioned taste aversions. Neurons from decerebrate preparations did, however, retain the broad sensitivity across stimuli that characterized taste cells in intact preparations. It was also typical that most neuron response profiles from decerebrates could be grouped into 3 loose clusters with peak sensitivities to acid-salt, salt or sugar. An analysis of similarities among stimulus activity profiles indicated that Na-Li salts, sugars and an acid-quinine complex represented 3 groups of stimulus quality; in intact animals, the primary distinction was between sweet and non-sweet stimuli. Moreover, the response to sodium saccharin lost its bitter component in decerebrates. These findings were in general agreement with those derived from acute decerebrate rats.

Animals↗
PubMed1991

Single neurone studies of opioid tolerance and dependence at the ventrobasal thalamic level in an experimental model of clinical pain, the arthritic rat.

The aim of this electrophysiological study was to investigate the effects of an acute injection of morphine (1 mg/kg i.v.) or the opioid antagonist naloxone (0.6-2 mg/kg i.v.) on thalamic ventrobasal (VB) neuronal activities recorded in arthritic rats rendered tolerant/dependent by pretreatment with relatively low doses of morphine. Recordings were performed in animals immobilized by i.v. injections of gallamine triethiodide (Flaxedil) and artificially ventilated under a moderate gaseous anesthesia (mixture of one-third O2, two-thirds N2O, 0.5-0.6% halothane). This level of anesthesia, as checked by the electrocorticogram, was stable and appeared sufficiently deep, since no sign of suffering or stress could be detected. The efficacy of morphine on VB neuronal responses induced by mild stimulation of the joints was greatly reduced in morphine-pretreated arthritic rats, compared to naive animals (mean neuronal inhibition of 35 vs 85%, respectively). This indicates that the tolerance phenomena observed in behavioral studies are reflected at the VB level, on neurons involved in pain processes. In addition, naloxone (0.6, 1 and 2 mg/kg i.v.) induced a dramatic increase in the evoked (52, 88 and 93%) and spontaneous (64, 211 and 292%) VB neuronal activities recorded in morphine-pretreated arthritic rats, while these activities were not significantly altered in naive arthritic rats. The time-courses of the modifications induced by naloxone in morphine-pretreated arthritic animals were similar to those of the naloxone-precipitated morphine withdrawal observed in freely moving rats. These findings may represent the neuronal correlate at the VB level of the withdrawal response and/or the hyperalgesia induced in tolerant arthritic rats by high doses of naloxone.

Animals↗
PubMed1992

Discharge response of cerebellar Purkinje cells to stimulation of C-fiber in cat saphenous nerve.

Experiments were performed in cats under chloralose anaesthesia and immobilized by Flaxedil. The discharge responses of cerebellar Purkinje cells (PC) were recorded with a microelectrode. The spontaneous activities of PC consisted of simple spike (SS) and complex spike (CS). When the saphenous nerve was stimulated at a low intensity, which elicited the A-fiber input only, the discharge responses (A-CED) consisted of an early component with short latency and late component with long latency in PC-SS and PC-CS. After A-fibers were blocked selectively by the polarizing current, the stimulation at the strength of C-fiber suprathreshold evoked the characteristic responses (C-CED) of PC-SS and PC-CS with middle latency. However, the C-CED could not be evoked by the inputs of A- and C-fibers simultaneously. These results suggested that the pure C-fiber input reaching the cerebellar PC passed through not only climbing fibers, but also mossy fibers, and elicited the characteristic responses (C-CED); these responses were neither the early component nor late component of the A-CED. When A- and C-fiber were activated at the same time, the C-CED might be inhibited by the A-fiber inputs.

Animals↗
PubMed1975

Amygdala and masseteric reflex. I. Facilitation, inhibition and diphasic modifications of the reflex, induced by localized amygdaloid stimulation.

The changes in amplitude of the monosynaptic masseteric reflex (MR), induced by stimulation of the amygdaloid area for the defence reaction (N. basalis, pars magnocellularis) and in other subdivisions of the amygdaloid complex, were studied in cats with spinal section maintained under Flaxedil. Simultaneously, the the effects of stimulation on the tonic activity of the masseteric nerve were observed. A maintained facilitation of the MR was elicited by stimulation of the lateral nucleus, the parvocellular portion of the basal nucleus and the cortical nucleus, while the reflex was inhibited during stimulation of the medial-most portion of the posterior amygdala. Diphasic changes of the MR amplitude (initial facilitation followed by delayed inhibition) were regularly observed when stimulating the magnocellular portion of the basal nucleus. These diphasic changes were closely correlated with the previously described diphasic resporatory and cardiac responses elicited from the same are (Bonvallet and Gary Bobo 1972). The initial facilitation probably corresponds to the "alerting" stage of the defence reaction and the delayed inhibition, associated with cortical, respiratory and cardiac activation, to the "defensive" stage of the reaction. Stimulation of the same area also provokes tonic or rhythmical discharges of the masseteric motoneurons which frequently occur during the delayed inhibition of the MR. The main efferent pathway mediating these motor effects is probably the ansa lenticularis.

Amygdala↗
PubMed1978

Auditory brain stem potentials with alcohol.

Auditory brain stem potentials were recorded from unrestrained rats and from cats paralyzed with Flaxedil, before and after ingestion of intoxicating dosages of alcohol. The acute effect of alcohol was a cumulative increase in the central conduction times of successive brain stem potential peaks. Statistically significant latency changes were found for peaks attributed to neural structures as far peripherally as the medulla. This depressive influence of alcohol on sensory transmission was independent of variations in stimulus intensity and body temperature.

Acoustic Stimulation↗
PubMed1983

Visual evoked potentials to light flash in cats: is a frontal sinus reference electrode truly indifferent?

In flaxedilized cats, visual cortex evoked potentials (VEPs) to an intensity series of brief light flashes were recorded differentially using either a screw over frontal sinus or an insect pin in neck muscle as the reference electrode. At the same time EPs from the cornea (the ERG) and frontal sinus were recorded differentially against the neck muscle electrode. The EP recorded from the frontal sinus screw was a miniature of the ERG recorded from the cornea, with the same latencies and shape as the ERG but only 10-30% of its amplitude. At a fast presentation rate (1/sec) the amplitude of the ERG, and consequently the frontal sinus potential, decreased with increasing intensity of light flash, whereas at a slow presentation rate (1/3 or 1/5 sec) the ERG and frontal sinus potential increased in response to all but the highest intensities. The location of the reference electrode and the rate of light flash presentation had the following effects on visual cortex EP amplitudes. A frontal sinus reference increased the amplitudes of early components (less than 100 msec) of the VEP. Also, VEP amplitudes as a function of flash intensity yielded slopes which tended to be positive at a slow presentation rate and negative at a fast presentation rate. This effect is in accord with the rate dependent slopes of the frontal sinus potential.

Animals↗
PubMed1975

Effects of the intra-arterial injection of bradykinin into the limbs, upon the activity of mesencephalic reticular units.

The changes in firing rate of mesencephalic reticular units after intra-arterial injection into the limbs of a potent nociceptive agent, bradykinin, were studied in cats (unanesthetized, immobilized with flaxedil and hyperventilated). 30 per cent of the d35 studied cells were affected, 56 per cent were excited, 23 per cent inhibited and 5 per cent had mixed effects. Among the 75 excited cells, the activation of 16 of them seemed to related to the arousa- processes (group A); for 56 cells the increase seemed dire-tly dependent on the nociceptive stimulation itself (group B). The changes of firing rate were repruducible; their latencies and durations were of the same order as the latencies and duration of the nociceptive reactions and painful sensation s, which have been obtained in animals and men after bradykinin injections. The modifications induced by bradykinin administration were suppressed by Ketamin and Thiopental.

Acoustic Stimulation↗
PubMed1983

Periaqueductal gray inhibition of trigeminal subnucleus caudalis unitary responses evoked by dentine and nonnoxious facial stimulation.

The possible pain inhibitory effects of periaqueductal gray (PAG) stimulation were investigated in cats anesthetized with Nembutal and immobilized with Flaxedil. Unitary responses evoked by electrical stimulation of the upper canine dentine and by cutaneous facial noxious and nonnoxious stimuli were recorded extracellularly from the trigeminal subnucleus caudalis. A bipolar electrode was introduced into the PAG to test the effects of PAG excitation on the trigeminal response to dentine (TRED) and cutaneous nonnoxious stimulation. In some experiments, a similar electrode was lowered into the contralateral posterior thalamus to study the antidromic activation of subnucleus caudalis cells and the effects of thalamic stimulation on the TRED. Dentine stimulation evoked brief (6- to 15-ms) bursts of 1 to 10 spikes with 3- to 25-ms latencies. Most units (88%) were also activated by cutaneous facial stimulation. Stimulation of the posterior thalamus had no effect on the TRED or on responses to cutaneous stimulation, but activated antidromically 10% of the units. In 71% of the units PAG stimulation inhibited the TRED. In some of those cases (12%), the inhibitory effect persisted 30- to 60 s. The PAG stimulation could produce paradoxical effects, potentiating the TRED evoked by threshold intensity and inhibiting the TRED elicited by suprathreshold stimulation. About one-half the PAG points evoked detectable effects. Their location had no clear topographical distribution, although ventral sites were more potent than dorsal sites. Responses evoked by nonnoxious facial stimulation were also inhibited by the PAG.

Animals↗
PubMed1975

Serotonin in the lateral geniculate.

Serotonin was introduced, by means of a fine cannula, into the lateral geniculate body of cats immobilized with Flaxedil and artificially ventilated, while the electrical activity at the point of injection was monitored by means of microelectrodes. Doses of 1.25 to 30 mug dissolved in 0.5 to 2.0 mul of saline produced, in 2-30 min, changes in electrical activity characteristic of synchronization: increase in the rhythmicity and in the amplitude of the spontaneous gross waves and increase in the clustering of the spontaneous neuronal action potentials. At the same time the activity of neurons which produced action potentials of high amplitudes was decreased, the activity of neurons which produced action potentials of low amplitudes was increased. Action potentials of different amplitudes were produced, in this case, by neurons of different types. Thus, in the lateral geniculate as in other thalamic nuclei studied in previous investigations, the synchronization of spontaneous activity seems to require the simultaneous excitation and inhibition of two different types of neurons. The action of serotonin on activity evoked by stimulation with brief flashes of light was limited to the decrease in the amplitude of the average gross response and the inhibition of only one type of neuron. This suggests that, in the lateral geniculate body, serotonin may be implicated in different ways in the different network structures responsible for the development of spontaneous as contrasted with evoked activity.

Action Potentials↗
PubMed1979

Olivo-cerebellar activity during harmaline-induced tremor.A 2-[14C]deoxyglucose study.

The specific neuronal activity of the olivo-cerebellar system of the cat under the effect of harmaline has been studied using the 2-[14C]deoxyglucose method. The results obtained in animals treated with tremogenic doses of harmaline, but immobilized with flaxedil, have been compared with those of non-treated controls. An increased radioactivity in specific regions of the olivo-cerebellar system including parts of the medial and dorsal accessory olive and the corresponding receiving molecular layer have been found. No involvement of the granule cell layer nor of the nuclear cells has been observed. It is therefore suggested that the tremogenic rhythmicity of the cerebellar output is organized uniquely by an increased climbing fiber input.

Alkaloids↗
PubMed1990

Involvement of solitary tract nucleus in control of nociceptive transmission in cat spinal cord neurons.

In cats anesthetized with Nembutal and immobilized with Flaxedil, extracellular recordings were made from dorsal horn neurons and lamina X neurons in the lumbar spinal cord. The nociceptive responses of these neurons elicited by peripheral nerve stimulation were significantly inhibited by stimulation of the nucleus tractus solitarius (NTS) at low intensity without any noticeable cardiovascular reaction. As usual, the late response or C-response was found to be preferentially inhibited by NTS stimulation as compared with the early response or A-response. The effective current intensity for NTS stimulation-produced inhibition ranged from 80 microA to 200 microA. Stronger inhibition was induced when the stimulating site was within or in the immediate vicinity of the NTS. There was no significant difference in the efficacy of the NTS stimulation-produced inhibition of nociceptive response between dorsal horn neurons and lamina X neurons. A similar inhibitory effect was elicited by microinjection of monosodium glutamate into the NTS area. The results demonstrate that the NTS may be involved in the control of nociceptive transmission at the spinal cord level.

Animals↗
PubMedDate not supplied

Analysis of circulation of neuronal activity in the waking cortex.

It is well known that the rhythmic activity of the cerebral cortex is closely associated with a highly organized circulation of neuronal impulses through the networks in which the activity develops. The present study has attempted to determine by quantitative methods, the consistency of this circulation and of its association with the cortical waves, over relatively long periods. Cortical gross waves and neuronal activity have been recorded by means of arrays of extracellular microelectrodes, in freely moving cats as well as in cats immobilized with flaxedil. Autocorrelations have been performed on trains of rhythmic waves and on associated clusters of action potentials; cross-correlations and multiple correlations have been performed between waves and action potentials and between action potentials generated by different groups of neurons. It has been found that the rhythmicity of the waves, the rhythmicity of the associated clusters of action potentials, the time and phase relations between them, and the circulation of neuronal activity through the networks, remain highly consistent over periods as long as two hours.

Action Potentials↗
PubMedDate not supplied

Effects of melatonin on spontaneous and evoked neuronal activity in the mesencephalic reticular formation.

The acute effects of melatonin on the spontaneous activity of single cells in the mesencephalic reticular formation were studied in 40 male rats unanesthetized and immobilized with Flaxedil. One hundred and ten neurons were explored. Only 64 modified their spontaneous activity after the intravenous administration of melatonin. This response consisted of an increase in neural firing (6 neurons), decrease (55 neurons) and biphasic response of decrease and increase (3 neurons). When the effect of melatonin on the evoked activity in the mesencephalic neurons by peripheral stimulation (sciatic and photic) was checked an increase of the number of neurons that showed inhibitory responses to photic stimulation was found. No changes in blood pressure and EEG were observed at the doses of melatonin used (200, 400 and 600 micrograms/100 g of body weight). However, with doses of 600 micrograms a tendency toward synchronization was seen in the EEG. The present observations indicate an inhibitory effect of melatonin on the spontaneous neuronal activity of the mesencephalic reticular formation. This effect may contribute to the changes in the sleep-wakefulness cycle and anticonvulsant action attributed to this hormone.

Animals↗