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At least 1,621 records · Page 90Linked to original sources
PubMed1987

Electrophysiological peculiarities of cortical inputs to the cat red nucleus.

Complex multicomponent EPSPs of the red nucleus rubro-spinal neurons evoked by stimulation of the sensorimotor cortex and associative fields of the parietal cortex were studied in acute pentobarbitalized cats by intracellular recording technique. Complex cortical EPSPs were recorded in 2/3 of the neurons studied. Components of the EPSPs in question were distinguished by using stimulation of various frequency and intensity. The first component of the EPSPs appearing at the lowest threshold was found to have a short and stable latency, stable rising time for depolarization and was able to follow high frequencies of stimulation. The second component was more variable, although in some EPSPs it too had a short latency, was stable enough and, like the first component could be classified as monosynaptic. The complex character of the EPSPs recorded persisted after the removal of the cerebral gray and was observed when stimulating the white matter so excluding its cortical origin. The first two components of the EPSP were evoked by corticofugal impulsation propagating at an average velocity of 18.5 m/s and 7.5 m/s being supposedly the result of activation of the slow-conducting pyramidal and cortico-rubral neurons. In some rubro-spinal neurons they were characterized by a fast rising phase being apparently an electrophysiological manifestation of the activation of axosomatic synapses.

Afferent Pathways↗
PubMed1989

Reappraisal of projection levels of the corticospinal fibers in the cat, with special reference to the fibers descending through the dorsal funiculus: a WGA-HRP study.

The precise course and termination levels of the corticospinal tract (CST) in the cat were studied using the anterograde transport of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Following injection of WGA-HRP into the pericruciate (sensorimotor) cortex on one side, we observed the precise caudal termination levels of the CST fibers in the lateral and ventral funiculi. Simultaneously, the bilateral CSTs descending through the dorsal funiculus of the spinal cord were identified. Anterogradely labeled CST fibers within the lateral and ventral funiculi were observed bilaterally to reach the level of the third sacral (S3) spinal segment, which is lower than that ever described. The lowest level of the CST fibers within the dorsal funiculus, however, reached the level of the first sacral (S1) spinal segment. In conclusion, this study demonstrates that, in the cat, there exist 6 different CSTs (crossed and uncrossed lateral, ventral, dorsal) and that the termination levels of the lateral and ventral CSTs are much lower than those described in previous reports.

Animals↗
PubMed1990

An electrophysiological study of trigeminal commissural interneurons in the anaesthetized rabbit.

The physiological characteristics of intertrigeminal area, nucleus oralis tau and supratrigeminal interneurons terminating in the contralateral-trigeminal motor nucleus were studied. Their antidromic conduction velocities were found to be between 3.7 and 16.3 m/s and most units had ipsilateral oral and peri-oral low threshold mechanoreceptive fields. Many received convergent inputs from both mandibular and maxillary divisions of the trigeminal nerve as well as the sensorimotor cortex.

Action Potentials↗
PubMed1992

Overgrowth and pruning of dendrites in adult rats recovering from neocortical damage.

Unilateral lesions to the forelimb representation (FL) area of the rat sensorimotor cortex caused a time-dependent increase in the dendritic arborization of layer V pyramidal neurons in the contralateral homotopic cortex. The increase in arborization was maximum at 2-3 weeks after the lesion, following which there was a partial reduction in dendritic branching. These neural morphological changes may be related to post-lesion behavioral changes in the use of the forelimbs.

Analysis of Variance↗
PubMed1992

Cortically evoked excitatory synaptic transmission in the cat red nucleus is antagonised by D-AP5 but not by D-AP7.

Extracellular recordings were made from magnocellular red nucleus neurons (mRN) in alpha-chloralose (50 mg/kg, iv.) anaesthetised cats. Iontophoretically applied N-methyl-D-aspartate (NMDA) excited the neuronal firing which was antagonised by 4 selective NMDA receptor antagonists: 2-amino-5-phosphonopentanoate (AP5), 2-amino-7-phosphonoheptanoate (AP7), RS-4-(phosphonomethyl) piperazine-2-carboxylic acid (PMPC) and R-4-(3-phosphonopropyl) piperazine-2-carboxylic acid (CPP), whereas AMPA responses were uneffected. Monosynaptic excitatory responses were produced by stimulation of the sensorimotor cortex. These responses were reduced and often abolished by AP5 and PMPC but not by AP7 or CPP. It is postulated that two NMDA receptor subtypes exist on mRN neurones.

2-Amino-5-phosphonovalerate↗
PubMed1992

Responses of globus pallidus neurons to cortical stimulation: intracellular study in the rat.

The responses of globus pallidus (GP) neurons to stimulation of the sensorimotor cortex, the neostriatum, and the subthalamic nucleus were intracellularly recorded in anesthetized rats. Stimulation of the cortex evoked a sequence of postsynaptic responses including an initial short EPSP, a short IPSP, and a late EPSP with multiple spikes in most of the repetitively firing GP neurons. The response pattern was very similar to those evoked by striatal stimulation, except that the latencies were longer. An acute knife cut placed immediately caudal to the substantia nigra caused no significant change in the responses to cortical and striatal stimulation. Stimulation of the subthalamic nucleus evoked a short latency EPSP overlapped with an IPSP. The polarity of all the IPSPs was reversed by a Cl- injection. A systemic injection of picrotoxin abolished all the IPSPs and unmasked large depolarizations with multiple spikes. An ibotenic acid lesion of the subthalamic nucleus eliminated both the initial short latency and late EPSPs to cortical and striatal stimulation and disclosed a prominent IPSP. Stimulation of the lesioned subthalamic nucleus also evoked large, short latency IPSPs without noticeable EPSPs. These results indicate that (i) the IPSPs evoked by cortical, striatal, and subthalamic stimulation were mediated by a GABAA receptor, (ii) both the initial and late EPSPs to cortical and striatal stimulation involved activation of the subthalamic nucleus but not brainstem nuclei, and (iii) cortically derived signals mediated through the neostriatum (i.e. long latency IPSPs) and the subthalamic nucleus (i.e. short latency EPSPs) converged on most GP neurons.

Animals↗
PubMed1992

Induction of c-Fos immunoreactivity in the rat forebrain by conditioned and unconditioned aversive stimuli.

The protein product of the c-fos proto-oncogene was immunocytochemically localized in forebrain regions of adult male Lewis rats subjected to a physically aversive footshock stimulus or a Pavlovian-conditioned, non-aversive, auditory stimulus. Animals receiving the conditioned stimulus were first conditioned by repeatedly pairing electric footshock, the unconditioned stimulus (US), with an auditory cue, the conditioned stimulus (CS). These animals were later tested with the CS in the absence of the US, a procedure which, like footshock itself, suppresses immune function. In animals exposed to the conditioned or unconditioned stressor, c-Fos was strongly expressed in cells of the paraventricular nuclei (PVN) of the hypothalamus, some of which contain corticotropin-releasing hormone (CRH), and other forebrain areas directly associated with autonomic function, the ventral lateral septal nuclei (LSV), the medial amygdaloid nuclei (AME), the sensorimotor cortex, the basal ganglia and thalamic nuclei. Control animals exhibited very little or no c-Fos in the above areas. The identified forebrain nuclei can now be targeted for further study aimed at elucidating their role in stress-induced immune alteration.

Animals↗
PubMed1993

Benzodiazepine receptor binding following chronic treatment with naloxone, morphine and met-enkephalin in normal rats.

The effects of chronic administration of naloxone, morphine and met-enkephalin on benzodiazepine (BDZ) receptor binding in rat brain were determined 2 and 50 days after treatments were accomplished. Two days after naloxone treatment (75 micrograms/h s.c. for 14 days), enhanced BDZ receptor binding was observed in cingulate, frontal, piriform, entorhinal and sensorimotor cortices; amygdala complex, hippocampus, substantia nigra and central gray. Two days after morphine treatment (20 mg/kg i.p. daily for 6 days), increased BDZ receptor binding was detected in cingulate, frontal, piriform, entorhinal and sensorimotor cortices; amygdala complex, hippocampus and substantia nigra. Two days after met-enkephalin treatment (10 micrograms/h i.c.v. for 6 days) enhanced BDZ receptor binding was shown only in sensorimotor cortex. No significant changes were observed 50 days after the treatments were completed. These data indicate an important interaction between GABAergic and opioid peptide systems.

Animals↗
PubMed1994

Pharmacological characterisation of excitatory synaptic transmission in the cat red nucleus in vivo.

Extracellular recordings were made from the magnocellular neurones of the red nucleus (mRN) in anaesthetised cats. A study was made of the effects of selective excitatory amino acid receptor antagonists on excitatory monosynaptic responses evoked from the sensorimotor cortex (SMC) and cerebellar interpositus nucleus (IPN). Iontophoretically applied CNQX and NBQX antagonised both SMC and IPN responses whereas, D-AP5 inhibited the SMC response but was ineffective to the IPN. At currents that selectively antagonised NMDA responses, CPPene had no effect on either SMC or IPN responses. 7-chlorokynurenate inhibited both SMC and IPN responses but required currents that antagonised both AMPA and NMDA responses and was therefore acting in a non-selective manner. Iontophoretically applied glycine was inhibitory to both agonist and synaptic responses, whilst D-serine potentiated NMDA responses but did not enhance monosynaptic responses of the SMC. However in the presence of either 7-chlorokynurenate or high currents of CNQX that reduced the SMC synaptic activation of the mRN neurones, D-serine attenuated the inhibitory action of these antagonists. It is concluded that monosynaptic responses from the SMC are mediated by both NMDA and non-NMDA receptors whereas the monosynaptic responses evoked from the IPN are mediated only by non-NMDA receptors. The lack of effect of CPPene is consistent with the postulate that two NMDA receptor subtypes are present on mRN neurones.

Animals↗
PubMed1994

Propagation of hippocampal seizure activity arising from the hippocampus: a local cerebral blood flow study.

We studied the propagation of spike discharges and the changes in local cerebral blood flow (LCBF) by means of the electroencephalogram (EEG) and autoradiographs to elucidate the underlying mechanism and the propagation pathway in rats with limbic seizures. Seizures were induced by the unilateral microinjection of kainic acid (KA) into the dorsal hippocampus during which behavioral, EEG and LCBF changes were documented. Overall, the results indicate an initial spreading to the contralateral hippocampus from the ipsilateral hippocampus, followed by activation of the ipsilateral amygdala, other limbic structures, striatum and sensorimotor cortex. Finally, seizure activity spreads to the ipsilateral globus pallidus, substantia nigra, subthalamic nucleus, thalamus, septum and parietal cortex. The activation of the contralateral hippocampus in the KA model studied here occurs earlier than in the acute amygdaloid seizure model. Elucidation of the mechanisms underlying this difference in the propagation pathway will require the application in parallel of techniques examining these and other aspects of seizure activity.

Animals↗
PubMed1995

Increase in the calcium level following anodal polarization in the rat brain.

The accumulation of calcium ions (Ca) was examined in the rat brain by means of 45Ca autoradiography following the application of a weak anodal direct current to the surface of the sensorimotor cortex. Repetition of the anodal polarization with 3.0 microA for 30 min caused more Ca to accumulate in the cerebral cortex. The degree and extent of accumulation was greater in the hemisphere ipsilateral to the polarization than in the other. Accumulation was also noted in the hippocampus and thalamus. Ca accumulation was detected after 24 h and it remained virtually constant up to 72 h after the last polarization. The results suggest that a long-lasting disturbance of Ca homeostasis is involved in the cortical plastic changes seen following anodal polarization.

Animals↗
PubMed1995

Suppression of motor cortical excitability by magnetic stimulation of the cerebellum.

EMG responses of the relaxed right thenar muscle evoked by magnetic stimulation over the sensorimotor cortex were suppressed by magnetic conditioning stimulation over the occiput. The optimal interstimulus interval for reduction of the EMG amplitude was 4-6 ms. The optimal conditioning position and induced current direction were 3-4 cm below the inion when the induced current in the center of the figure-8 coil flowed from right to left horizontally. It differed from that for activating the descending motor pathway. We consider this suppression to be due to the inhibition of motor cortex excitability caused by stimulation of the dentato-thalamo-cortical pathway at the dentate nuclei or superior cerebellar peduncle.

Adult↗
PubMed1977

Effects of voluntary isometric and isotonic activity on late transcortical reflex components in normal subjects and hemiparetic patients.

When the median nerve is stimulated at the wrist during voluntary contraction of m. abductor pollicis brevis (APB) EMG activity of this muscle contains different distinct responses: a direct muscular response (M response), a spinal reflex response (S response) and a third late reflex response, first described by Upton et al. (1971) as a second volitional reflex response (V2). Comparison of this very likely long-loop reflex involving pathways to and from the cortical level (therefore labelled C response) under isometric (hold) and isotonic (move) contraction revealed a strong facilitation of the response under the latter condition. Repetitive trains of stimuli had stronger facilitatory effect on the occurrence of this late reflex response than single stimuli. Cutaneous stimuli of the median nerve afferents did not exhibit M and S responses but definite late excitatory responses with similar latencies to the C responses. In cases of hemiparesis (mild to severe loss of sensorimotor control of finger movements) the C response was diminished, delayed or absent. These findings together with recent primate and human experimental work support the hypothesis of a transcortical stretch reflex. On the premise that muscular as well as cutaneous afferents contribute to the afferent cortical input the late C response can be interpreted as the efferent component. The C response may be a valuable aid in the diagnosis of small lesions of the sensorimotor cortex and internal capsule.

Adult↗
PubMed1979

Changes in seizure susceptibility, sleep time and sleep spindles following thalamic and cerebellar lesions.

The present experiment attempted to clarify conflicting evidence on the relationship of sleep spindles to seizure activation. Seizure thresholds were calculated in minutes post-injection following IP administration of the convulsant drug monomethylhydrazine (MMH) to cats with lesions intended to alter the occurrence of spontaneous 12-15 c/sec sleep spindles recorded from sensorimotor cortex. Twelve cats with bilateral cortical and subcortical recording electrodes were divided into 3 groups receiving electrolytic lesions in the dentate nucleus (group I), the ventrobasal (VB) thalamus (group II), or in one of various 'control' regions (group III). Lesion sites in group III animals avoided primary afferent pathways to VB thalamus, destruction of which has been found to enhance sleep spindle activity, and included cerebellar white matter and ventral pontine tegmentum. Prior to the MMH trials, baseline EEGs were obtained during pre- and post-lesion conditions. Following the MMH trial, lesions were verified histologically. Results of the MMH trial revealed that animals with dentate and ventrobasal thalamic lesions showed elevated seizure thresholds and slow wave sleep times relative to their own pre-lesion EEG baselines and to the pre- and post-lesion baselines of control animals. Furthermore, an increased incidence of sleep spindles was associated with dentate lesions while animals with ventrobasal thalamic lesions showed a shift in frequency from 8-11 c/sec to 12-15 c/sec activity during that state. These findings are compatible with the view that sleep spindles do not facilitate seizure activation and may, in fact, exert a protective influence.

Animals↗
PubMed1980

Topography of scalp recorded potentials evoked by stimulation of the digits.

The amplitude of the primary positive deflection, P24, was measured in each wave form recorded from a 36-channel scalp electrode array placed over sensorimotor cortex. Electrical stimulation of contralateral little, middle, index finger, or thumb produced wave forms possessing common features, but the location of peak P24 amplitude depended upon the digit stimulated. With thumb stimulation peak P24 amplitude was located approximately two-thirds the distance from midline to sylvian fissure, while stimulation of the other digits resulted in more medially located topographic peaks. These shifts correlate with previous descriptions of body-part representation in somatosensory cortex and suggest that at least certain wave form deflections recorded from the scalp provide accurate localization of their underlying neural generators.

Adult↗
PubMed1981

Central beta rhythm during sensorimotor activities in man.

Blocking or desynchronization of the central beta rhythm prior to and parallel to voluntary movement was found in 31 of 33 normal subjects investigated. The beta blocking was short lasting (1-3 sec), very often accompanied by blocking of the mu rhythm and localized in the central region. Phasic beta desynchronization was also observed after somatosensory stimulation. The beta rhythm showed a bilateral symmetrical blocking pattern with unilateral movement or stimulation. Patients with unilateral cerebral ischaemia showed an asymmetric blocking response and therefore demonstrated a high degree of hemispheric independence of the rhythmic generating systems. Central beta desynchronization is, therefore, a normal physiological phenomenon caused by activation processes of the sensorimotor cortex and detectable on the scalp very easily with closely spaced electrodes.

Beta Rhythm↗
PubMed1984

Somatosensory evoked potentials to mechanical disturbances of positioning movements in man: gating of middle-range components.

Somatosensory evoked potentials (SEPs) and EMG responses to mechanical disturbances of positioning movements of the index finger were recorded from normal subjects who performed smooth flexions against the constant load of a torque motor in order to reach a specified target zone. According to a random series 60% of the movements were disturbed by step increases or decreases of the load which subjects had to compensate for (movement condition, MC). As control procedures (a) the same stimuli were applied while the subject had to maintain a constant finger position against the same load (hold condition, HC), and (b) comparable mechanical stimuli were administered to the stationary relaxed finger (resting condition, RC). In MC and HC, the EMG responses consisted of a long-latency (53-61 msec) reflex component, and a 'voluntary' component (98-134 msec). In all 3 conditions, the sequential SEP deflections measured over the sensorimotor cortex included peaks P85 (ipsilateral), N150 (bilateral) and P220 (bilateral). A contralateral N90 component (onset latency 55-60 msec), present in HC and RC, was markedly reduced or absent in MC. Neither in the preceding nor in the consecutive SEP components were there any significant condition-dependent differences, though the N150 showed a trend to diminished amplitude in MC as well. The suppression of SEP components in MC is discussed in terms of efferent and afferent 'gating' actions exerted on the somatosensory input during movement.

Adult↗
PubMed1986

Evoked potentials from passive elbow movements. II. Modification by motor intent.

Subjects were instructed to remain passive or to react to a forearm perturbation by opposing the imposed movement. Evoked potentials (EPs) were recorded at 8 scalp sites in both conditions. In the React condition, reflexes were observed in the EMG (mean onsets of 67 and 81 msec) and the EP was modified. Source derivation techniques revealed that the earliest cortical response (31 msec) across the central sulcus was not changed. Therefore the intention to react did not seem to affect afferent transmission to the primary sensorimotor cortex. Two periods of modulation were observed. In both, parietal and frontal potentials were modulated together, prior to the reflex components. After 70 msec, the pattern of potential gradients which occurred in the Passive case was accelerated and intensified in the React condition. The overall effect was to focus a larger zone of negativity over motor cortex at the time of triggered EMG output (109 msec). The earlier changes in cortical activity could be causally related to the appearance of the late stretch reflex. Since parietal and frontal areas were principally involved and not the motor area, it is suggested that the former exert a modulatory influence on spinal and brain-stem reflex centres.

Elbow↗