Stimulation Of Thalamic Nuclei Research Articles

Dendritic action potentials of pyramidal tract neurons in the cat sensorimotor cortex

The intracellular activity of pyramidal tract neurons was studied during electrical stimulation of ventrolateral and ventroposterolateral thalamic nuclei in acute experiments on cats immobilized by myorelaxants. Somatic action potentials were observed and spontaneous spikes were also produced by single and rhythmic stimulation of the thalamic nuclei at the rate of 8–14 Hz, by iontophoretic application of strychnine, and by intracellular depolarizing current pulses. These potentials had a relatively low and variable amplitude of 5–60 mV and are presumed to be dendritic action potentials. It is postulated that these variable potentials arise in the dendrites of pyramidal neurons with multiple zones generating such activity. No interaction was observed where somatic and dendritic action potentials occur simultaneously. The possible functional role of dendritic action potentials is discussed.

Properties of monosynaptic connections between callosal neurons and specific thalamic nuclei

A comparative analysis of monosynaptic afferent and efferent connections of callosal neurons and target neurons of transcallosal fibers with neurons of the specific ipsilateral thalamic nuclei (ventral posterolateral, ventral posteromedial, ventral lateral, and anteroventral) was undertaken on the sensomotor cortex of unanesthetized rabbits, using an electrophysiological method. Differences were demonstrated between callosal neurons and target neurons of transcallosal fibers with respect to monosynaptic inputs from the thalamic nuclei and pathways proceeding toward these structures and (or) entering the pyramidal tract. Among target neurons, compared with callosal neurons, more cells had descending projections (54 and 14%, respectively). Monosynaptic action potentials arose in 22% of target neurons in response to stimulation of specific thalamic nuclei, whereas no such responses occurred in callosal neurons. Projections of target neurons into thalamic nuclei were shown to be formed both by independent fibers and by axon collaterals of the pyramidal tract. It is postulated that the distinctive properties thus discovered indicate significantly greater convergence of influence of thalamic relay neurons on the target neurons; this determines differences known to exist in characteristics of receptive fields and spontaneous and evoked activity of callosal neurons, on the one hand, and of neurons excited synaptically by transcallosal stimulation, on the other hand.

Effects of electrical stimulation of various midline thalamic nuclei on the bilateral release of dopamine from dendrites and nerve terminals of neurons in the nigro-striatal dopaminergic pathways

The effects of electrical stimulation of midline thalamic nuclei on the release of [ 3H]dopamine ([ 3H]DA) were determined in both substantiae nigrae (SN) and caudate nuclei of halothane-anesthetized cats using the push-pull cannula method. [ 3H]DA release was increased in the four structures following stimulation of the interanteromedialis nucleus (IAM) but only enhanced in both SN when nucleus reuniens (RE) was stimulated. In contrast, no effect was detected after delivery of the stimuli to nucleus centralis medialis. These results indicate that the anterior part of the thalamic massa intermedia (IAM and RE particularly) is involved in the bilateral regulation of DA release from nerve terminals and dendrites of the nigro-striatal dopaminergic neurons.

Origins of post synaptic potentials evoked in spiny neostriatal projection neurons by thalamic stimulation in the rat.

Stimulation of thalamic intralaminar nuclei or structures along the intrathalamic trajectory of thalamostriatal axons evoked complex EPSPs and subsequent hyperpolarizations in rat neostriatal spiny neurons identified by intracellular injection of horseradish peroxidase and/or antidromic activation from substantia nigra. In intact urethane-anesthetized rats, the initial EPSP portion of the response consisted of several components and lasted up to 75 ms. Short (1-10 ms) latency components exhibiting latency variations suggestive of a polysynaptic origin were often observed, and sometimes were the earliest components of the response. However, individual components of the excitatory response could not be clearly distinguished in most neurons and the earliest excitatory component usually appeared to be monosynaptic. After large acute aspiration lesions of ipsilateral cerebral cortex, the early polysynaptic EPSP components of thalamic-evoked EPSPs were absent or greatly attenuated. This suggested that most or all of the short latency polysynaptic EPSP components arose via a thalamo-cortico-striatal route. A short latency (1.6-4.0 ms) monosynaptic EPSP and a second excitatory component with a longer and more variable latency (8-28 ms) remained intact after acute decortication. These were not dependent upon intact corticothalamic or corticostriatal axons, since they were both still present in experiments performed as long as 4 days following ipsilateral hemidecortication. The longer latency excitatory response was shown to be polysynaptic by its latency variation with changes in stimulus intensity and frequency. This component of the response was abolished after acute thalamic hemitransections separating thalamostriatal neurons from their axons. In these experiments, stimulation of thalamostriatal axons rostral to the transection continued to evoke monosynaptic EPSPs in neostriatal spiny neurons. These EPSPs ranged from 1.8 to 3.0 ms in latency, had peak amplitudes up to 11 mV and were 20-37 ms in duration.

Effects of unilateral electrical stimulation of various thalamic nuclei on the release of dopamine from dendrites and nerve terminals of neurons of the two nigrostriatal dopaminergic pathways

The role of several motor and intralaminar thalamic nuclei in the regulation of dopamine release from terminals and dendrites of the nigrostriatal dopaminergic neurons was investigated in halothane-anaesthetized cats. For this purpose, the effects of the unilateral electrical stimulation of various thalamic nuclei on the release of newly synthesized [ 3H]dopamine were simultaneously determined in both substantiae nigrae and caudate nuclei using the push-pull cannula method. The electrical stimulation of the motor nuclei was the only one to induce asymmetric changes in the four structures since [ 3H]dopamine release was enhanced in the ipsilateral caudate nucleus and reduced in the contralateral structure while opposite responses were observed in the corresponcling substantiae nigrae. A reduction of [ 3H]dopamine release occurred in the four structures or only in the contralateral substantia nigra and caudate nucleus following the stimulation of the parafascicularis nucleus and the adjacent. posterior part of the nucleus centrum medianum or of the nucleus centralis lateralis and the adjacent paralaminar part of the nucleus medialis dorsalis, respectively. The stimulation of the anterior part of the nucleus centrum medianum, which in contrast to other thalamic nuclei examined, receives few nigral inputs, selectively enhanced [ 3H]dopamine release in the contralateral substantia nigra. No significant changes in [ 3H]dopamine release were seen either in the substantiae nigrae or in the caudate nuclei following the stimulation of midline thalamic nuclei. These results indicate that the motor and intralaminar thalamic nuclei exert multiple and selective influences on the release of dopamine from terminals and/or dendrites of the dopaminergic neurons. They also further support a role of thalamic nuclei in the transfer of information from one substantia nigra to the contralateral dopaminergic neurons. The possible involvement of connections between paired thalamic nuclei was underlined by the observations of evoked potentials in contralateral homologous nuclei following unilateral stimulation of motor, or some intralaminar, nuclei. The present report provides new insights on the mechanisms contributing to the reciprocal and/or bilateral regulations of nigrostriatal dopaminergic pathways.

Ontogenetic development of rhythmic thalamo-cortical phenomena in the rat

MAREŠ, P., D. MAREŠOVÁ, S. TROJAN AND J. FISCHER. Ontogenetic development of rhythmic thalamo-cortical phenomena in the rat. BRAIN RES. BULL. 8(6) 765–769 1982.—Three rhythmic cortical phenomena (rhythmic afterdischarges, incremental responses and self-sustained after-discharges formed by spike-and-wave rhythm) were elicited by electrical stimulation of thalamic nuclei during ontogenesis in rats. All three phenomena could be recorded for the first time at the age of 12 days and they matured until the 18th postnatal day. Possible explanation for the delayed development of these rhythmic thalamo-cortical phenomena in comparison with single thalamo-cortical responses are discussed.

Effect of isolated and combined stimulation of thalamic nuclei on the character of functional connections between sensomotor cortical neurons.

1. Investigation of interneuronal relations in the cat sensomotor cortex revealed different types of dependence in the discharge of individual neuron pairs both during their spontaneous activity and in the after-period of thalamic stimulations. 2. Repeated isolated stimulations of the thalamic nuclei (VPL and VL) led to marked transformation of the “excitatory” component of the “inhibitory—excitatory” relationship dur1ing discharge of two neighboring neurons. The transformations differed in cases of stimula tion of the two different nuclei: whereas stimulation of VPL mainly weakened the “excitatory” component of the “inhibitory—excitatory connection,” stimulation of VL usually distinctly enhanced it. 3. The character of interneuronal influences formed during the action of isolated thalamic stimulations underwent further modification in the course of combined stimulations of the same nuclei. 4. Changes in interneuronal dependence arising as a result of prolonged thalamic stimulation could last for several minutes after cessation of the stimulations.

Unit responses in area 21 of the suprasylvian gyrus to stimulation of thalamic association and specific nuclei

Unit responses in area 21 of the suprasylvian gyrus to stimulation of thalamic association and specific nuclei

Prosencephalic mechanisms of ECoG desynchronization in Cerveau isole cats

In acute and chronic rostral cerveau isoleé cats (section at frontal plane 3 or 4) high-frequency stimulation of basal forebrain regions induced “tonic” ECoG desynchronization with abrupt abolition of spindles, which always outlasted the period of stimulation. Exploration of the preoptic area showed that the maximal effect followed stimulation of regions immediately above the chiasma. High-frequency stimulation of the posterior hypothalamus induced ECoG activation similar in all respects to that after basal forebrain stimulation in both acute and chronic preparations. The most effective area was found to be situated ventro-medially. Parallel to neocortical desynchronization theta waves were induced in the dorsal hippocampus by both preoptic and hypothalamic activation. This effect disappeared after acute coagulation of septal nuclei. In acute cerveau isolé preparations high-frequency stimulation of the ventral amygdala led to no significant change in the background synchronization. Stimulation of the dorsal amygdala induced “phasic” ECoG activation which did not outlast the stimulation period. Occasionally a “tonic” cortical arousal limited to the ipsilateral hemisphere could be seen following stimulation of dorsal nuclei. In no case did olfactory stimulation modify the ECoG synchronization. An absence of cortical activation was also found during high-frequency stimulation of intralaminar thalamic nuclei. Intravenous injection of barbiturate (from 2 to 20 mg/kg) increased the spontaneous synchronization while it progressively shortened and eventually abolished the electrocortical activation induced by stimulation of the basal forebrain and the posterior hypothalamus. It is suggested that in preparations with transection of the brain-stem at a rostral level both the anterior (preoptic) and posterior hypothalamus have a “tonic” desynchronizing influence on the cortex, which requires no support from the reticular activating system of the brain-stem. The control exerted by dorsal amygdala on the electrical activity of the cortex appears instead to be mediated by the brain-stem.

Trigeminothalamic neurons in nucleus caudalis responsive to tactile, thermal, and nociceptive stimulation of monkey's face.

1. A total of 113 trigeminothalamic neurons and over 200 presumed interneurons of nucleus caudalis (0-5 mm below the obex) and subjacent reticular formation were studied in rhesus monkeys anesthetized with chloralose or nitrous oxide. Each cell was characterized in terms of its antidromic responses to stimulation of ventral posterior medial and/or posterior thalamic nuclei and to three types of stimuli applied to its receptive field: a) graded 5-s temperature shifts at a rate of 9 degrees C/s from 35 degrees C to final temperatures of 20-52 degrees C, generated by a contact thermode; b) graded intensities of electrical stimulation to determine the conduction velocities of converging primary afferent fiber populations; and c) mechanical stimulation ranging from light touch to pinch with serrated forceps. 2. This analysis yielded five classes of units distinguished by the range of responses to mechanical stimuli and by the convergence of different primary afferent fiber populations. These five classes were found among both trigeminothalamic neurons and neurons which could not be antidromically activated. Class 1 units exhibited rapidly adapting responses to hair movement or light touch and received only A-beta primary afferent input. Class 2 units responded to light touch and pressure with maintained discharges and received A-beta primary afferent input. Class 3 units responded maximally to pinch with serrated forceps but also were activated by light touch and pressure. They received A-beta, A-delta, and C fiber input. Class 4 units responded to firm pressure and maximally to pinch with serrated forceps. These units had A-delta and sometimes C fiber input. Class 5 units responded only to pinch with serrated forceps and had exclusive A-delta fiber input. Some cells in all five classes responded antidromically to stimulation of the thalamus. Antidromic action-potential latencies of classes 1,2, and 3 units were shorter than those of classes 4 and 5 units (P less than 0.001). Receptive-field sizes were usually small (1-2 cm2) for classes 1, 2, 4, and 5 units, and larger for class 3 units (one to three trigeminal divisions). The marginal layer of nucleus caudalis contained mostly classes 4 and 5 units, some class 3 units, but no classes 1 or 2 units. The superficial portion of the magnocellular layer contained mostly classes 1 and 2 units, while neurons at the base of this layer contained class 3 units and some classes 4 and 5 units. Cells in the sujacent reticular formation included all 5 classes but showed a tendency to have large receptive fields (greater than 1 trigeminal division). 3. Neurons responding to noxious thermal stimuli (44-52 degrees C) were classes 3 or 4 units. The response patterns of classes 3 and 4 units to noxious thermal stimuli were similar. No classes 1 or 2 units and only one class 5 unit responded to increases in skin temperature. Thermal thresholds ranged from 38 to 50 degrees C and most heat-responsive units responded monotonically to temperatures between 45 and 52 degrees C...

Three components of incrementing PSPs of pyramidal tract cells evoked by stimulation of thalamic nuclei

Three components of incrementing PSPs of pyramidal tract cells evoked by stimulation of thalamic nuclei

Sensory afferents to the caudate nucleus

In awake immobilized cats, stimulation of nonspecific thalamic nuclei (NCM, DM) elicits evoked potentials in the head of the caudate nucleus (CN). The evoked potentials (EP) in the ventral part of CN are opposite in sign to those recorded in the dorsal region of CN. The points of polarity reversal are grouped in the lower third of CN. Peripheral sensory stimuli (somatic and visual) evoked potentials with a 20 msec latency. These evoked potentials change their polarity in the same region as the thalamic evoked responses. Visual and somatic responding areas overlap widely. The advantage of bipolar recordings for better localization is discussed.

Inhibition of Gonadotropin Secretion Induced by Stimulation of Thalamic Nuclei

The effect of electrochemical stimulation (anodic current, 100 micronA/30 sec) of thalamic nuclei was studied in nonanesthetized freely-behaving rats bearing chronic implanted electrodes and plastic cannulae inserted into the jugular vein for blood sampling. Stimulation of the anterior thalamic nuclei, the nucleus (n.) mediodorsalis thalami (MD) and the n. posteromedianus thalami at 2 p.m. on the day of proestrus prevented spontaneous ovulation and the release of LH which takes place on that day. No effect on ovulation or LH release was observed after stimulation of the n. lateralis thalami, the n. ventralis thalami or other thalamic nuclei or after passing a cathodic current through the n. MD. Stimulation of the n. MD resulted also in a significant decrease of the elevated serum LH levels found after an injection of progesterone into ovariectomyzed estrogen-primed rats. These results indicate that nuclei of the medial thalamic region are capable of inhibiting LH secretion. No stimulatory influence of LH release was observed after thalamic stimulation in ovariectomized estrogen-treated rats.

An intracellular study of thalamocortical synapses in the orbito-insular cortex

Intracellular recordings were made in multimodal orbito-insular cortex in response to electrical stimulation of thalamic association nuclei. Four types of responses were observed: One was short latency excitation; another was short latency excitation followed by inhibition; the third was long latency inhibition followed by excitation; the fourth was rhythmic afterdischarge. The initial excitatory response is viewed as being due to direct thalamocortical input and the later inhibitory ones to intracortical inhibition. The results resemble those obtained in lemniscal systems having specific thalamic relay nuclei, and they provide correlates for recent anatomical reports concerning the projections of the frontal orbital cortex.

Unit responses of the cat parietal association cortex to stimulation of reticular and anteroventral thalamic nuclei

Responses of 124 neurons in the anterior division of the middle suprasylvian gyrus to stimulation of the reticular (R) and anteroventral (VA) nuclei and the pulvinar (Pulv.) of the thalamus were studied in acute experiments on unanesthetized cats immobilized with D-tubocurarine. Responses of 70 neurons to stimulation of R and Pulv. were investigated. Altogether 51.5% of the cells of this group responded to stimulation of R while 38.6% of neurons responded to stimulation both of R and of Pulv., indicating convergence of afferents from nonspecific and associative nuclei of the thalamus on these neurons. Responses of 54 cells to stimulation of VA and Pulv. were investigated. The tests showed that 72.2% of neurons responded to stimulation of VA and convergence of afferents from VA and Pulv. was found in 29.6% of neurons. As a rule neurons were excited in response to stimulation of R and VA. Inhibition was observed in only one neuron in response to stimulation of R and in six neurons in response to stimulation of VA. The latent period of responses to stimulation of R varied between 2.2 and 37.0 msec, of VA from 6.0 to 35.5 msec, and of Pulv. from 2.1 to 35.0 msec. The length of the latent periods to stimulation of nonspecific and associative nuclei were compared for groups of neurons for which convergence of afferent influences from R and Pulv. or from VA and Pulv. was found. The question of connections of R and VA with the parietal association cortex is discussed.

Effects of thalamic midline nuclei stimulation upon lateral geniculate transmission in rats: inhibition of principal cells and excitation of internuncial cells.

Effects of low-frequency stimulation of thalamic midline nuclei (MID) upon unitary activities of principal (P) and internuncial (I) cells of the lateral geniculate body were examined in urethane-anesthetized rats. P-cells responsed to single shocks to the optic tract (OT) with single spikes at short latencies (initial spike, IS), followed by a phase of inhibition which lasted for more than 150 msec and ended with a burst of grouped discharges (late discharge, LD). Excitability of P-cells, assessed with the response probability of IS to testing OT shocks, was reduced for about 300 msec after single shock stimulation of MID. Usually this excitability depression became evident about 20 msec after MID shocks and was maximum from 50 to 100 msec. LDs were made more vigorous when MID shocks were given almost simultaneously with testing OT shocks. This was interpreted that MID stimulation induced an inhibition in P-cells and it summed with that induced by OT stimulation. That the MID-induced inhibition of P-cells was due to IPSPs was proved by the quasi-intracellular recording. I-cells, the units fired repetitively by single OT shocks and have been presumed to be inhibitory neurons acting upon P-cells, were found to receive from MID stimulation an excitatory effect followed by an inhibitory one of long duration. It was suggested that the primary inhibition of P-cells by low-frequency stimulation of MID would be a direct consequence of the primary excitation of I-cells.

Electrophysiological studies on cerebello-cerebral projections in the cat.

1. Cerebello-cerebral projections were electrophysiologically investigated in cats under light Nembutal anaesthesia. Marked responses were produced by stimulation of the interpositus and the lateral nucleus of the cerebellum not only in the pericruciate but also in the suprasylvian cortical areas, both areas being contralateral to the cerebellar nuclei stimulated. Medial nucleus stimulation set up little or no response in the cerebral cortex. 2. The previous electrophysiological study on thalamo-cortical (T-C) projections showed two different kinds of responses in the cortex due presumably to two different T-C projection systems, i. e., deep and superficial T-C responses (see Sasaki et al., 1970). According to laminar field potential analysis, the response in the pericruciate area is characterized by a deep T-C response which is often followed by a superficial T-C response, whereas the response in the parietal cortex consists of a pure superficial T-C response. Intracellular potential changes in cortical neurones elicited by cerebellar nucleus stimulation were consistent with the results of laminar field potential analysis. 3. Comparison between laminar field potentials in the same cortex produced by thalamic and cerebellar nucleus stimulation suggests that the response in the pericruciate cortex is mediated by the ventral lateral nucleus and that the response in the parietal cortex is relayed by the ventral anterior nucleus of the thalamus.

Alterations of defensive reactions in the rat after cholinergic stimulation of midline thalamic nuclei

Cholinergic stimulation of the midline thalamic nuclei reduced active avoidance of a shock prod, passive avoidance of a highly discriminable shock object, and freezing in the presence of stimuli previously associated with shock. However stimulation did not alter flinch or jump thresholds to foot shock, or thresholds for escape from foot shock. These results suggest that alterations of the activity of the midline nuclei directly affect defensive reactions, rather than altering sensory, motor, or general activity processes which may influence avoidance responding.

Thalamic and cerebellar influence on single units of the cat cuneate nucleus

The activity of single units was extracellularly recorded from cuneate nucleus in cats anesthetized with Nembutal. Stimulation by trains of four impulses, 300/sec, of nonspecific thalamic nuclei and cerebellar fastigial nuclei could modify the spontaneous and evoked activity of both interneurons and relay cells. The peripherally evoked and spontaneous activity of CTR neurons were depressed for 150–200 msec after thalamic and cerebellar stimuli in, respectively, 40 and 30% of the cells while the antidromic lemniscal potential was never affected by these stimuli. Both excitatory and inhibitory effects were detected on cuneate interneurons after thalamic and cerebellar stimulations. The nonspecific thalamic nuclei stimulation evoked potentials in 70% of the interneurons and the fastigial nuclei in 40%. Most of the analyzed interneurons showed a characteristic convergence of peripheral and central (cortical, thalamic, reticular, cerebellar) excitatory and inhibitory effects. In interaction experiments both cerebellar and thalamic (conditioning) stimuli could inhibit the activity evoked by different test (cortical, reticular, and peripheral nerves) stimuli, at intervals of 10–200 msec. Inhibitory effects between cerebellar and thalamic stimulations were also observed. These results show that both nonspecific thalamus and cerebellum presynaptically control the sensory cuneate nucleus transmission through the effect exerted on the cuneate interneurons. This effect is considered to be mediated by the brain stem reticular formation.

Reactions of neurons of the orbitofrontal cortex to stimulation of optic thalamic nuclei

The reactions of 288 neurons of the orbitofrontal cortex (OFC) to stimulation of the posteroventral (VP), ventral anterior (VA), and reticular (R) nuclei, as well as the median center (CM) of the thalamus, were investigated in acute experiments on cats. OFC neurons can be divided into four groups by their reactions to stimulation of thalamic nuclei: 1) those which respond with an increase in the frequency of the discharges to single and serial stimuli with a frequency of up to 20/sec; 2) those which respond doubtfully to single stimuli with a frequency of 4–12/sec; 3) those which respond with inhibition of the background impulses; 4) those which do not respond to stimulation of the nuclei. Stimulation of the thalamic nuclei evoked responses of OFC neurons with a large scatter of the latent period duration. The responses of neurons to stimulation of the VP (mean latent period 19.1±6.1 msec) had the shortest latent period (sometimes less than 3–4 msec). Reactions with a longer latent period developed upon stimulation of the VA (23.8±7.4 msec) and CM (42.8±12.8 msec). The uniqueness of the links of the OFC with the various optic thalamic nuclei is shown in an analysis of the material obtained and possible methods of the activation of the neurons of this region from thalamic structures are discussed.