Ventrolateral Thalamic Nucleus Research Articles

Localization of neuropeptide Y-immunoreactive cells and fibres in the brain of the Japanese quail

In the present study, we have demonstrated, by means of the biotin-avidin method, the widespread distribution of neuropeptide Y (NPY)-immunoreactive structures throughout the whole brain of the Japanese quail (Coturnix coturnix japonica). The prosencephalic region contained the highest concentration of both NPY-containing fibres and perikarya. Immunoreactive fibres were observed throughout, particularly within the paraolfactory lobe, the lateral septum, the nucleus taeniae, the preoptic area, the periventricular hypothalamic regions, the tuberal complex, and the ventrolateral thalamus. NPY-immunoreactive cells were represented by: a) small scattered perikarya in the telencephalic portion (i.e. archistriatal, neostriatal and hyperstriatal regions, hippocampus, piriform cortex); b) medium-sized cell bodies located around the nucleus rotundus, ventrolateral, and lateral anterior thalamic nuclei; c) small clustered cells within the periventricular and medial preoptic nuclei. The brainstem showed a less diffuse innervation, although a dense network of immunopositive fibres was observed within the optic tectum, the periaqueductal region, and the Edinger-Westphal, linearis caudalis and raphes nuclei. Two populations of large NPY-containing perikarya were detected: one located in the isthmic region, the other at the boundaries of the pons with the medulla. The wide distribution of NPY-immunoreactive structures within regions that have been demonstrated to play a role in the control of vegetative, endocrine and sensory activities suggests that, in birds, this neuropeptide is involved in the regulation of several aspects of cerebral functions.

Immunohistochemical localization of serotoninergic, enkephalinergic, and catecholaminergic cells in the brainstem and diencephalon of a cartilaginous fish, hydrolagus colliei

We localized serotonin (5-HT), leu-enkephalin (LENK), and tyrosine hydroxylase (TH) immunoreactive cells in the brain of a holocephalian, Hydrolagus colliei, by use of antibodies made in rabbit and the peroxidase-antiperoxidase technique. Only three locations contained TH+ cells, the caudal myelencephalon, the locus coeruleus, and the diencephalon. Of these locations, the diencephalon contained the most cells and the locus coeruleus the least cells. The caudal TH+ myelencephalic cells formed a single large group that spanned both the dorsal and ventral portions of the brain (A1A2). The diencephalic TH+ cells were located in the posterior tuberculum, in the ventromedial and ventrolateral thalamic nuclei, and in the inferior lobe of the hypothalamus. Hydrolagus differed from mammals and the elasmobranchs, their sister group, in that no substantia nigra (A9), ventral tegmental area (A10), or A5 cell group was found. Distribution of LENK+ and 5-HT+ cells were similar to each other; the raphe nuclei contained most of the 5-HT+ and LENK+ cells. These 5-HT+ and LENK+ cells were found at all rostrocaudal levels of the myelencephalon. The nucleus reticularis magnocellularis, reticularis paragigantocellularis lateralis, the ventral met- and mesencephalon (B7 and B9 cell groups), the hypothalamus, and the pretectal area contained additional 5-HT+ and LENK+ cells. The solitary complex contained LENK+ cells but not but 5-HT+ cells. A dorsal raphe nucleus, which is the largest 5-HT+ cell group in mammals, was absent in Hydrolagus. A dorsal raphe nucleus is present in one galeomorph shark radiation but is absent in three radiations of batoids (rays, skates, and guitarfish). Thus even within cartilaginous fish, there are differences in the distribution of neurochemicals and possibly nuclei within their brains.

Organization of the cerebellum in the pigeon (Columba livia): II. Projections of the cerebellar nuclei

The projections of the deep cerebellar nuclei in the pigeon have been delineated using autoradiographic and histochemical (WGA-HRP) tracing techniques. A medial (CbM) and lateral (CbL) cerebellar nucleus are recognized and CbM may be further partitioned into internal, intermediate, and intercalate divisions. As in mammals, most extracerebellar projections of CbM travel in the fasciculus uncinatus (FU); the rest travel with those of CbL in the brachium conjunctivum (BC). In the pigeon, both of these pathways are bilaterally but primarily contralaterally projecting systems. FU is a predominantly descending tract, with terminations within (1) the vestibular complex, (2) a column of contiguous medial reticular nuclei from pontine to caudal medullary levels; (3) the plexus of Horsley portion of the parvicellular reticular formation, continuing through the nucleus centralis medullae oblongatae, pars dorsalis, into intermediate layer VII of the cervical spinal cord, down to cervical segment 8-9; (4) the lateral reticular nucleus and the paragigantocellular reticular nucleus; (5) the dorsal lamella of the inferior olive. Rostrally FU terminals are found in the locus ceruleus and dorsal subcerulean nucleus. Minimal FU projections are also seen to the motor trigeminal nucleus and the subnucleus oralis of the descending trigeminal system. A small projection from the intercalate division of CbM travels in BC and projects upon the midbrain central grey, the intercollicular nucleus, the lateral tectal periventricular grey, the stratum cellulare externum and, sparsely, upon the dorsolateral thalamus. The bulk of BC originates from the lateral cerebellar nucleus and consists of a massive ascending and a small descending branch. The ascending system projects upon the red nucleus and the dorsally adjacent interstitial nucleus of Cajal and midbrain central grey, the prerubral fields continuing into the stratum cellulare externum, the nucleus intercalatus thalami, the ventrolateral thalamic nucleus, the medial spiriform nucleus, the nucleus principalis precommissuralis, the nucleus of the basal optic root, the nucleus geniculatus lateralis pars ventralis, the dorsolateral thalamus, including the dorsal intermediate posterior, and the dorsolateral intermediate and anterior nuclei. BC also contains axons from the infracerebellar nucleus, which projects upon the trochlear and the oculomotor nuclei. The descending branch of BC distributes to the papilioform nucleus, the medial pontine nucleus, the gigantocellular and paramedian reticular nuclei, and, minimally, the rostral portions of the medial column and ventral lamella of the inferior olive. Taken in conjunction with data on amphibia and reptiles the present findings suggest that the fundamental ground plan of vertebrate cerebellar organization involves a medial and lateral cerebellar nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of catecholaminergic transmission deficiency upon neuronal responses of the ventrolateral thalamic nucleus evoked by stimulation of cerebellar and pallidal inputs

Neuronal responses of the ventrolateral thalamic nucleus (VL) to the afferent stimulation were studied in chronic experiments on cats before and after injection of haloperidol and droperidol in cataleptic doses. As distinct from the reactions of intact animals, after injection of neuroleptics the initial excitative VL neuronal responses to the cerebellar stimulation were characterized by the irregularity of manifestation and the variability of the latent period, the responses in the form of burst discharges appeared. During pallidal stimulation a statistically significant increase in the number of initial inhibitory responses consisting of two periods of the background activity suppression with an excitation phase separating them was observed, while monophase inhibitory reactions prevailed (68%) in intact animals. Under neuroleptics the reactions with rhythmic alternation of excitative and inhibitory periods of the impulsive activity with frequency 3-5/s. occurred. It is suggested that revealed peculiarities of the neuronal reactions result from the hyperpolarizing state of the VL neurons because of the augmented external inhibitory actions due to a blockade of dopamine receptors of the nigrostriatal system or because of the reduced depolarizing influences under the break of the central alpha-adrenergic transmission.

Visuomotor relearning after brain damage crucially depends on the integrity of the ventrolateral thalamic nucleus.

The role of the ventrolateral thalamic nucleus (VL) has been analyzed in the phase of motor recovery that takes place when the execution of a previously learned movement has been perturbed by damage to another brain area. Cats were trained to perform a reaching movement toward a moving target-spot; they underwent bilateral brain lesions after performance had stabilized. A VL lesion induced a very transient increase of reaction time. The lesion of the main thalamic relay of the visual extrageniculate pathway (LP) severely disrupted accuracy and reaction time but was followed by full recovery. When both lesions were performed together, the deficits were similar to those induced by LP lesion alone, although they were more pronounced. However, the functional compensation was incomplete, and furthermore, the recovery of accuracy crucially depended on regular testing. These results support the involvement of VL in motor learning or relearning.

Effects of experimentally induced deficiency of catecholaminergic transmission on neuronal activity in the ventrolateral thalamic nucleus

Background activity was investigated in 272 neurons of the ventrolateral thalamic nucleus (VLTN) before and after systemic administration of neuroleptics (haloperidol and droperidol) at cataleptic doses by means of extracellular techniques during chronic experiments on cats. Autocorrelation and spectral analysis revealed regularly-occurring changes in the background activity rate of VLTN neurons, the periodicity of which changed by fractions of seconds (0.2–0.8 sec), seconds (1.5–10 sec), or tens of seconds (12–30 sec). While numbers of neurons with individual types of periodic activity did not exceed 6–8% in intact animals, it did increase to 18–30% after administering neuroleptics. Raised numbers of neurons with two types of regularly occurring processes within a single spike train were also noted. Experimentally-produced data were compared with findings from clinical observations. Quantities of neurons with different variations in the periodicity of their firing activity reached 19–46% in patients with parkinsonism but did not exceed 4–8% in those with torsion dystonia. The genesis of raised rhythmic firing in thalamic neurons occurring with parkinsonism is thought to be associated with impaired catecholaminergic (both dopaminergic and α-adrenergic) transmission.

Properties of associative long-lasting potentiation induced by cellular conditioning in the motor cortex of conscious cats

Mechanisms of long-lasting potentiation of synaptic responses induced in the thalamocortical and recurrent collateral pathways of the pyramidal tract were studied in intracellular recordings from the motor cortex of unanesthetized, chronically implanted cats. The observations provide the first description of long-lasting potentiation in the unanesthetized neocortex in vivo. Monosynaptic excitatory postsynaptic potentials of 2–5 mV in amplitude were evoked as test responses by stimulation of the pyramidal tract and thalamic ventrolateral nucleus at 0.1–0.5 Hz frequency. Pressure microinjections of drugs and ions were also performed during intracellular recordings. In the first series of experiments, test synaptic responses were paired with intracellular current injection-induced action potentials at an interstimulus interval set between 0–200 ms and 0.1–0.5 Hz frequency. Pairings (30–100 ×) induced long-lasting potentiation of the test responses in 58% of cells. The increased synaptic responses typically initiated action potentials and their potentiation usually lasted over the period of recordings. Increases in amplitude of synaptic responses were not correlated with statistically significant changes in electrical membrane properties (resting potential, input resistance, time constant, spike threshold) or parameters of action potentials and their afterpotentials. The failure to induce increases in synaptic efficacy by unpaired stimuli (pseudoconditioning) demonstrated the associative property of the long-lasting potentiation. In a second series of experiments, differential cell conditioning was employed. This paradigm induced long-lasting potentiation of the explicitly paired synaptic response without noticeable modification of unpaired or pseudorandomly paired synaptic responses tested conjointly in the same neuron. These observations demonstrated the input-specificity of long-lasting potentiation. In a third series of experiments, sub-threshold depolarizing current pulses were summated with synaptic responses to induce firing in the recorded neuron during pairing. Long-lasting potentiation occurred in 55% of the summated synaptic inputs. Pseudoconditioning did not induce synaptic potentiation in these cells. In a fourth series of experiments, conditioning was employed in neurons in which firing activity was suppressed by an intracellularly injected lidocaine derivative. Long-lasting potentiation was induced in 50% of the attempts when synaptic responses were paired with current-induced depolarizations ≫ 30 mV. These results suggest that postsynaptic induction of long-lasting synaptic potentiation can be successful in the absence of postsynaptic sodium spikes in neurons of the motor cortex in vivo. In a fifth series of experiments, homosynaptic high-frequency tetanization (80–200 Hz for 5–15 s) was applied to the thalamocortical and recurrent pyramidal afferents. We were able to induce long-lasting potentiation by tetanization only in the pyramidal pathways. This is in contrast with low-frequency pairings that produced input-specific synaptic enhancement in both the thalamic and pyramidal pathways. The observations suggest that some mechanisms of the induction process of long-lasting potentiation may be different in these two pathways of the motor cortex.

Choline acetyltransferase immunoreactivity in the cat cerebellum

Choline acetyltransferase immunoreactivity was demonstrated in particular projection systems in cat cerebellum by combining immunohistochemistry, retrograde tracing and lesioning paradigms. The monoclonal antibody used in this study recognized a 68,000 mol. wt protein on immunoblots of cat cerebellum and striatum. Choline acetyltransferase immunoreactivity was localized to some neurons and varicose fibers in the cerebellar nuclei, and also to some mossy fibers and endings (rosettes), fiber plexuses around Purkinje cells, granule cells and parallel fibers in the cerebellar cortex. In addition, the presence of choline acetyltransferase-immunoreactive large cells, presumptive Golgi cells, in the granular layer was confirmed. In each cerebellar nucleus, choline acetyltransferase-immunoreactive neurons contained either large, medium-sized or small cell bodies and were distributed evenly in the entire nuclear domain. Large and medium-sized ones were frequently encountered. Choline acetyltransferase-immunoreactive mossy fibers and rosettes were most abundant in the vermal lobules I–III, VIII, IX and the simple lobule, moderately accumulated in the vermal lobules IV–VII, X, crus I and crus II, and less abundant in the paramedian lobule, paraflocculus and flocculus. Some granule cells with prominent dendritic claws and bifurcating parallel axons were immunolabeled in the entire vermis with infrequent occurrence in the remaining cortices. Following unilateral lesioning of the cerebellar nuclei with electrocoagulation or kainate injections, a reduction in number of choline acetyltransferase-immunoreactive fibers occurred ipsilaterally in the cerebellar cortex and contralaterally in the red nucleus, ventrolateral thalamic nucleus and ventroanterior thalamic nucleus. In addition, perikarya of some cerebellothalamic neurons were shown to contain choline acetyltransferase immunoreactivity. The results indicate that some nucleocortical, cerebellorubral and cerebellothalamic projections are cholinergic and that a subpopulation of cholinergic granule cell-parallel fibers exists.

Plastic synaptic reorganization in the sensorimotor cortex of adult cats after lesioning of the contralateral cerebellar nucleus interpositus

Intact cats and animals undergoing lesioning of the contralateral cerebellar nucleus interpositus between one and six months previously were used in this research, employing intracellular recording techniques and investigating the response of corticospinal neurons (CSN) to stimulating the aforementioned nucleus, the ipsilateral cerebellar nucleus interpositus, and the ventrolateral thalamic nucleus. A reduction was found in the stage of rise to peak in monosynaptic thalamocortical EPSP in CSN of operated animals, with a low axonal conduction velocity, pointing to distant terminal dendrosomatic sprouting and formation of new synapses at proximal sections of the CSN somatodendritic membrane. Findings are presented on formation of ipsilateral interpositothalamocortical projections duplicating similar contralateral projections in intact animals. Contralateral cortico-interposital collaterals were found in intact animals and similar sprouting of ipsilateral origin in those which had undergone surgery.

Relationship between thalamic projections and different areas of the parietal association cortex in cats

Thalamic neuronal projections to the parietal association cortex were investigated in cats applying techniques of retrograde axonal transport of two fluorescent dyes (primuline and fast blue). The dorsal thalamic pulvinar (PL) as well as the dorsal and caudal lateral posterior nucleus (LP) were found to project mainly to the central suprasylvian gyrus (CSSG), while the ventral PL and the ventrorostral LP send out projections to rostral sites of the same gyrus (RSSG). Neurons with dual labeling were found in the PL, LP, suprageniculate, anteroventral, and ventrolateral thalamic nuclei following a single injection of two different markers into the RSSG and CSSG, as well as the centrolateral, paracentral, and centromedial nuclei. Topical organization of sources of cortical projections within the PL-LP complex can apparently provide a high level of discrimination of visual signals by individual cortical units. At the same time, the RSSG and CSSG appear to function in harmony to a considerable extent during integration of information of differing cortical origin; this could point to a lack of differentiation on the part of the RSSG and CSSG, corresponding to feline cortical areas 5 and 7 approximately.

Changes in the activity of ventrolateral thalamic neurons and instrumental response after systemic administration of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Neuronal activity in the ventrolateral thalamus during execution of instrumental reaction before and after parenteral administration of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was investigated in samples of 81 and 70 cells, respectively. After a 5-day course of one 5 mg/kg MPTP injection daily, firing rate of neurons in which activity correlated with forelimb movement rose significantly; this activation increased in length during the initial, flexor, and extensor stages of motor response. Bradykinesia set in together with intensified neuronal activation in the animals. Microinjection of exogenous dopamine into the caudate nucleus brought about correction of motor disturbance and a reduced neuronal firing rate in the ventrolateral (thalamic) nucleus. It was deduced that the nigrostriatal system exercises inhibitory control over the activity of thalamic neurons associated with forelimb movement in thalamic neurons in intact animals.

Visuomotor relearning after brain damage crucially depends on the integrity of the ventrolateral thalamic nucleus.

Visuomotor relearning after brain damage crucially depends on the integrity of the ventrolateral thalamic nucleus.

Aspects of synaptic reorganization in the cat sensorimotor cortex after lesion of the symmetrically contralateral hemisphere

During the course of acute experiments, response in cortico-spinal neurons (CSN) to stimulating the ipsilateral ventral thalamic nucleus was investigated by extracellular recording techniques in intact adult cats and others with lesioning inflicted on the contralateral sensorimotor cortex 6–18 months previously. An accelerated stage of growth was noted in monosynaptic IPSP and CSN with slow-conducting axons in animals with surgically-induced lesion, suggesting reorganization of synaptic contacts within the CSN somatodendritic membrane. The collision test was applied to make a complete examination of arborization and of other aspects of CSN axons, as well as the presence of collaterals running to the ventrolateral thalamic nucleus and helping to form the ipsilateral pyramidal tract. The significance is discussed of plastic synaptic rearrangement in the ipsilateral thalamo-cortical reverberating system for formation of the efferent spike train during partial interhemisphere cortical deafferentation.

Connections of the caudal cerebellar interpositus complex in a new world monkey ( Cebus apella)

The afferent and efferent connections of the cerebellar interpositus complex were studied in a capuchin monkey ( Cebus apella) that had received a transcannular horseradish peroxidase implant into the caudal portion of the anterior interpositus nucleus and posterior interpositus nucleus. While the heaviest anterogradely labeled ascending projections were observed to the contralateral ventral posterolateral nucleus of the thalamus, pars oralis (VPLo), efferent projections were also observed to the contralateral ventrolateral thalamic nucleus (VLc) and central lateral (CL) nucleus of the thalamic intralaminar complex, magnocellular (and to a lesser extent parvicellular) red nucleus, nucleus of Darkschewitsch, zona incerta, nucleus of the posterior commissure, lateral intermediate layer and deep layer of the superior colliculus, dorsolateral periaqueductal gray, contralateral nucleus reticularis tegmenti pontis and basilar pontine nuclei (especially dorsal and peduncular), and dorsal (DAO) and medial (MAO) accessory olivary nuclei, ipsilateral lateral (external) cuneate nucleus (LCN) and lateral reticular nucleus (LRN), and to a lesser extent the caudal medial vestibular nucleus (MVN) and caudal nucleus prepositus hypoglossi (NPH), and dorsal medullary raphe. The heaviest retrograde labeling was corticonuclear Purkinje cells in the paramedian cerebellar cortex lateral to the vermis of lobules IV–VIII. Otherwise, retrogradely labeled sources of afferents were predominantly contralateral in the dorsal, dorsomedial, paramedian, and peduncular sectors of the basilar pons, NRTP, and dorsal accessory (DAO) and medial accessory (MAO) of olivary nuclei, but were predominantly ipsilateral in the LCN, LRN, and in the medullary reticular formation along the roots of the hypoglossal (XII) cranial nerve. It appeared that the connections with the contralateral dorsal basilar pons, NRTP, DAO and MAO, and ipsilateral LCN and LRN are reciprocal. There was only a small number of retrogradely labeled cells in the caudal MVN, caudal NPH, nucleus reticularis pontis caudalis, and pedunculopontine and medial parabrachial nuclei. A propensity of connections of the interposed complex with structures that receive input from the somatomotor cortex (area 4) was observed and is discussed.

Bilateral alterations in local cerebral glucose utilization following intranigral application of the GABAergic agonist muscimol

Rates of cerebral glucose utilization were measured by means of the autoradiographic 2-deoxy-D-[1-14C] glucose technique in 70 anatomically discrete central nervous structures in conscious awake rats following unilateral intranigral application of the GABAergic agonist muscimol. Intranigral injection of 1.3 microliters 1 microM muscimol (0.15 ng) induced increases in glucose consumption locally in the substantia nigra reticulata (by 87%), distally in the contralateral reticulata, red nucleus, nucleus accumbens, and prefrontal cortex, and bilaterally in the pyriform cortex, as compared to values in control animals. Intranigral injection of 1.3 microliters 1 mM muscimol (150 ng) effected a local metabolic activation in the substantia nigra reticulata (by 111% compared to the control group) and in compacta (by 18%), as well as a distal activation in the contralateral reticulata (by 39%) and contralateral compacta (by 29%). Beyond the structures affected by the lower dose, the higher dose of muscimol elicited widespread bilateral increases in glucose metabolism in the rat brain. Among the principal nigral reticulata efferent projections, the deep superior colliculi displayed ipsilateral metabolic activation (by 30%), whereas the parafascicular, mediodorsal, and ventromedial thalamic projecting areas, as well as the pedunculopontine nucleus, displayed bilateral activations compared to the control animals. The ventromedial and ventrolateral thalamic nuclei contralateral to the injected substantia nigra reticulata were 20% activated compared to the ipsilateral homologous structures and 30% activated compared to the control rats. The areas that send afferent projections to the reticulata (globus pallidus, entopeduncular and subthalamic nuclei) were mainly activated contralateral to the injected reticulata compared to values for control animals. In general, following intranigral muscimol (1 mM) injection, glucose metabolism was activated to a larger extent on the side contralateral to the injection than on the ipsilateral side. It is suggested that the present findings are due to a presynaptic nigral effect of muscimol on the GABAergic autoreceptors of the striatonigral terminals and to a consequent disinhibition of the reticulata GABAergic output.

Mapping the effects of motor cortex stimulation on somatosensory relay neurons in the rat thalamus: Direct responses and afferent modulation

Single unit recordings were used to map the spatial distribution of motor (MI) cortical influences on thalamic somatosensory relay nuclei in the rat. A total of 215 microelectrode penetrations were made to record single neurons in tracks through the medial and lateral ventroposterior (VPM and VPL), ventrolateral (VL), reticular (nRt), and posterior (Po) thalamic nuclei. Single units were classified according to their: 1) location within the nuclei, 2) receptive fields, and 3) response to standardized microstimulation in deep layers of the forepaw-forelimb areas of MI cortex. For mapping purposes, only short latency (1–7 msec) excitatory neuronal responses to the MI cortex stimulation were considered. Percentages of recorded thalamic neurons responsive to the MI stimulation varied considerably across nuclei: VL: 42.6%, nRt: 23.0%, VPL: 15.7%, VPM: 9.3%, and Po: 3.9%. Within the VPL, most responsive neurons were found in “border” regions, i.e., areas adjacent to the VL, and (to a lesser extent) the nRt and Po thalamic nuclei. The same parameters of MI cortical stimulation were used in studies of corticofugal modulation of afferent transmission through the VPL thalamus. A condition-test (C-T) paradigm was implemented in which the cortical stimulation (C) was delivered at a range of time intervals before test (T) mechanical vibratory stimulation was applied to digit No. 4 of the contralateral forepaw. The time course of MI cortical effects was analyzed by measuring the averaged evoked unit responses of the thalamic neurons to the T stimuli, and plotting them as a function of C-T intervals from 5–50 msec. Of the 30 VPL neurons tested during MI stimulation, the average response to T stimulation was decreased a mean 43%, with the suppression peaking at about 30 msec after the C stimulus. This suppression was more pronounced in the VPL border areas (−52% in areas adjacent to VL and nRt) than in the VPL center (−25%).

Analysis of Premovement Components of Movement-Related Cortical Potentials in Patients with Parkinson's Disease or Brain Tumors

We have recorded movement-related cortical potentials (MRCPs) preceding voluntary finger extension in patients with Parkinson's disease and in patients with brain tumors that may involve the motor system. Three components of potential shifts preceding the voluntary movement were identified in all subjects. There were no differences between the healthy subjects and those with Parkinson's disease, or between pre- and postoperative recordings from the same parkinsonian patients in terms of onset latencies and gradients of these potential shifts. There was no evidence of MRCPs from the depth electroencephalogram recorded from the thalamic ventrolateral (VL) nucleus. After removal of the cerebellar dentate nucleus along with a tumor, MRCPs were still identified. After removal of tumors from the supplementary motor cortex and frontal association cortex, a part of the MRCPs preceding the voluntary movement was absent. The generation of MRCPs was considered not to be greatly affected by the cerebellar system because: (1) no MRCPs were detected from the thalamic VL nucleus, which is the relay nucleus of the dentato-rubro-thalamic pathway, believed to be related to voluntary movement; (2) destruction of the VL nucleus did not cause any changes in the MRCPs recorded at other sites, and (3) the MRCPs did not disappear when the dentate nucleus, an output system, was excised.

Effect of NMDA and 2-amino-7-phosphonoheptanoate focal injection into the ventrolateral thalamic nucleus on the high pressure neurological syndrome in the rat

We report the effect of focal injections of N-methyl- d-aspartate (NMDA, 5 nmol) and 2-amino-7-phosphonoheptanoate (APH, 5 and 10 nmol) into the ventrolateral thalamic nucleus on behavioural symptoms of the high pressure neurological syndrome in rats. The injection of NMDA significantly lowers the threshold pressure for tremor and increases its intensity. The injection of APH significantly increases the threshold pressure for tremor and decreases its intensity. APH, 10 nmol, significantly increases the threshold pressure for myoclonus and convulsions. These protective effects are, however, less pronounced than those produced by either systemic injection of APH or its focal infusion into the basal ganglia output system.

Effects of systemic injection of neuroleptics on neuronal background activity in the cat ventrolateral thalamic nucleus

Background activity was recorded in 272 neurons of the ventrolateral thalamic nucleus before and after systemic haloperidol and droperidol injection at a cataleptic dose using intracellular techniques during chronic experiments on cats in a drowsy condition. Brief burster discharges lasting 5–50 msec and following on at a high intraburst spike rate (of 200–450 Hz) were characteristic of neuronal activity in intact animals. Regular discharges occurred at the rate of 2–2.5 Hz or occasionally 3–4 Hz in 15% of cells. Numbers of neurons with the latter activity pattern rose to 22 and 30%, respectively, following haloperidol and droperidol injection. Both irregular and prolonged (80–300 msec) regular discharges were recorded in one third of the total. A relatively low intraburst spike rate (of 60–170 Hz) was observed in 37% of cells following 10 days' haloperidol injection. These changes are thought to be produced by intensified inhibitory effects on neurons of the thalamic ventrolateral nucleus from the substantia nigra and reticular thalamic nucleus following blockade of dopaminergic and α-adrenergic receptors.

Mapping the Effects of SI Cortex Stimulation on Somatosensory Relay Neurons in the Rat Thalamus: Direct Responses and Afferent Modulation

We have used single-unit recording techniques to map the spatial distribution of the primary somatosensory (SI) cortical influences on thalamic somatosensory relay nuclei in the rat. A total of 193 microelectrode penetrations were made to record single neurons in tracks through the medial and lateral ventroposterior (VPL and VPM), ventrolateral (VL), posterior (Po), and reticular (nRt) thalamic nuclei. Single units were classified according to their (1) location within the nuclei, (2) receptive fields, and (3) response to standardized microstimulation in deep layers of the SI cortical forepaw areas. The SI stimulation produced short-latency (1- to 7-msec) excitatory responses in different percentages of neurons recorded in the following thalamic nuclei: VPL, 42.0%; Po, 25.0%; nRt, 16.4%; VL, 13.6%; and VPM, 9.9%. Within the VPL, the highest proportion of responsive neurons was found in the anterior region. Although most of the VL region was unresponsive, the caudal subregion bordering the rostral VPL showed some responsiveness (13.6% of neurons). In general, the spatial pattern of corticothalamic influences appeared to reciprocate the known thalamocortical connection patterns, but with a heterogeneity that was unpredicted. The same parameters of SI cortical stimulation were used in studies of corticofugal modulation of afferent transmission through the VPL thalamus. A condition-test (C-T) paradigm was implemented in which the cortical stimulation (C) was delivered at a range of time intervals before test (T) mechanical vibratory stimulation was applied to digit 4 of the contralateral forepaw. The time course of cortical effects was analyzed by measuring the averaged evoked unit responses of thalamic neurons to the T stimuli, and plotting them as a function of C-T intervals from 5 to 50 msec. Of the 20 VPL neurons tested during SI stimulation, the average response to T stimulation was decreased a mean of 36%, with the suppression peaking (at 49% inhibition of the afferent response) about 15 msec after the C stimulus. Considerable rostrocaudal variation was observed, however. Whereas neurons in the rostral VPL (near VL) were strongly inhibited (-69%), neurons in the middle and caudal VPL exhibited facilitations at long and short C-T intervals, respectively. This study establishes a specific projection system from the forepaw region of SI cortex to different subregions of the VPL thalamus, producing specific temporal patterns of sensory modulation.