Ventral Posterior Thalamic Nucleus Research Articles

Description of a large projection from the mesodiencephalic junction to the rostral red nucleus. An anatomical study in the rat and in the cat

Horseradish peroxidase (HRP) or wheat germ agglutinin conjugated to HRP (WGA-HRP) were deposited in the rostral pole (Rpc) of the red nucleus in 6 rats and 5 cats. In the rat, a zone of dense retrograde cell labeling and of diffuse axonal labeling occurred in the sub-pretectal area, a region which corresponds to the posterior thalamic nucleus (PT) of Bold et al. ( Brain Research, 12 (1984) 521–527). In the cat, a similar retrograde and anterograde pattern of labeling was observed. The labeled area extended from the deep pretectum up to the diencephalon above the dorsomedial aspect of the ventral posterior thalamic nucleus. In a second set of experiments, 14 rats received a tracer injection (HRP, WGA-HRP or Phaseolus vulgaris-leucoagglutinin) in the sub-pretectal area. The resultant pattern of labeling consisted in a heavy anterograde terminal labeling within the Rpc of the red nucleus. Sparse retrograde cell labeling also occurred in the Rpc.

The morphology of physiologically identified GABAergic neurons in the somatic sensory part of the thalamic reticular nucleus in the cat

Neurons with somatic sensory receptive fields were examined electrophysiologically in the thalamic reticular nucleus of the cat. All cells had receptive fields much larger than those of neurons in the ventral posterior nucleus and were driven by less readily defined somesthetic stimuli. Response latencies to peripheral or medial lemniscal stimulation were, on average, longer than in the ventral posterior nucleus and suggested activation of the reticular nucleus cells by collaterals of thalamocortical relay cell axons arising in the ventral posterior nucleus. When injected intracellularly with horseradish peroxidase, reticular nucleus cells displayed thin axons with intrareticular collaterals and diffuse branches through much of the ventral posterior and posterior thalamic nuclei. Dendrites ended in processes resembling synaptic terminals. Electron microscopic immunocytochemistry of the same part of the reticular nucleus revealed processes immunoreactive for glutamic acid decarboxylase and identifiable as both collateral axon terminals and presynaptic dendrites of GABAergic reticular nucleus cells. These synaptically linked reticular nucleus cells and, in addition, immunoreactive somata and presynaptic dendrites received synapses from at least three varieties of nonimmunoreactive profiles.

Unit responses of the ventral posterior and ventral lateral thalamic nuclei to electrical stimulation of the thalamic reticular nucleus

A microelectrode investigation was made of responses of 72 physiologically identified neurons of the ventral posterior (VP) and 116 neurons of the ventral lateral (VL) thalamic nuclei to electrical stimulation of the reticular (R) thalamic nucleus. Mainly those neurons of VP and VL (73.7 and 86.2% respectively) which responded to stimulation of the first motor area and nucleus interpositus of the cerebellum responded to stimulation of R; 19.8% of VL neurons tested responded to stimulation of R by an antidromic action potential with latent period of 0.5–2.0 msec and 46.6% of neurons responded by orthodromic excitation; 23% of orthodromic responses had a latent period of 0.9–3.5 msec and 77% a latent period of 4.0–21.0 msec; 19.8% of VL neurons tested were inhibited. Among IPSPs recorded only one was monosynaptic (1.0 msec) and the rest polysynaptic. It is postulated that both R neurons are excitatory and that the inhibition which develops in VL neurons during stimulation of R are connected mainly with activation of inhibitory interneurons outside the reticular nucleus.

Unit responses of the first and second somatosensory cortical areas to peripheral, thalamic, and cortical stimulation.

Unit responses of the first (SI) somatosensory area of the cortex to stimulation of the second somatosensory area (SII), the ventral posterior thalamic nucleus, and the contralateral forelimb, and also unit responses in SII evoked by stimulation of SI, the ventral posterior thalamic nucleus, and the contralateral forelimb were investigated in experiments on cats immobilized with D-tubocurarine or Myo-Relaxin (succinylcholine). The results showed a substantially higher percentage of neurons in SII than in SI which responded to an afferent stimulus by excitation brought about through two or more synaptic relays in the cortex. In response to cortical stimulation antidromic and orthodromic responses appeared in SI and SII neurons, confirming the presence of two-way cortico-cortical connections. In both SI and SII intracellular recording revealed in most cases PSPs of similar character and intensity, evoked by stimulation of the cortex and nucleus in the same neuron. Latent periods of orthodromic spike responses to stimulation of nucleus and cortex in 50.5% of SI neurons and 37.1% of SII neurons differed by less than 1.0 msec. In 19.6% of SI and 41.4% of SII neurons the latent period of response to cortical stimulation was 1.6–4.7 msec shorter than the latent period of the response evoked in the same neuron by stimulation of the nucleus. It is concluded from these results that impulses from SI play an important role in the afferent activation of SII neurons.

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...

The effects of tooth pulp stimulation in the thalamus and hypothalamus of the rat

The organization of the efferent projections from the spinal trigeminal nucleus oralis (Sp5O) to the diencephalon was studied in the rat using the anterograde tracer Phaseolus vulgaris leucoagglutinin. The present study confirms the existence of trigemino-thalamic pathways originating from the Sp5O and details their distribution. The main diencephalic targets of the Sp5O are the ventral posteromedial thalamic nucleus (VPM), the posterior thalamic nuclei (Po) and the ventral part of the zona incerta (ZIv), contralaterally, and the parvicellular part of the ventral posterior thalamic nucleus (VPpc), bilaterally. The distribution of these projections varies according to the dorso-ventral location of the injection sites: the dorsal part of the Sp5O projects to the medial part of the VPM and the Po, and to the caudal part of the ZIv, as well as to the VPpc. The ventral part of the Sp5O projects to the lateral part of the VPM and the Po and to the rostral part of the ZIv. These results suggest that the trigemino-diencephalic pathways originating from the Sp5O are involved in the processing of gustatory and somatosensory information.

An anatomic basis for multimodal thalamic units

Lesions were placed in the inferior colliculi of seven opossum and degenerating axons were traced to the dorsal thalamus with the Nauta technique. The sites of terminal degeneration included the medial geniculate body, ventral posterior, and posterior thalamic nuclei (PO). This wide region of distribution provides an anatomic basis for the existence of cells in the ventral posterior and PO nuclei that are responsive to auditory stimuli.

Gastric secretory response of the unrestrained cat following electrical stimulation of the cingulate, thalamus, and mesencephalon

The effect of intracerebral stimulation on the basal gastric secretory response was examined in unanesthetized, unrestrained cats equipped with a permanent gastric fistula and indwelling electrodes. Stimulation of the corpus callosum-cingulate gyrus area produced a significant increase in total acid output without concomitant behavioral and somatomotor changes. One of these responses was accompanied by an increase in pepsin output while the other showed a concurrent decrease in secretory volume and chloride output. Stimulation of the sites located in the ventral anterior and lateral posterior thalamic nuclei, cerebral peduncle-substantia nigra region, and reticular mesencephalic substance failed to elicit a significant gastric secretory response even at intensities which produced gross autonomic, behavioral and somatomotor changes. The results suggest that the corpus callosum-cingulate gyrus region plays an important role in regulating gastric secretory function. The responses appeared to be entirely neural in nature and compared favorably with those previously observed following amygdaloid and supraoptic stimulation.

Supersensitivity of the sensory cortex following partial deafferentation: Lesion of the ventral posterior thalamic nuclei

1. 1. The loss or diminution of the spontaneous electrical discharges of the sensory cortex following lesions or destruction of the ipsilateral ventral posterior thalamic nuclei is often only transitory (experiments in cats). It may be followed by a tendency to periodic burst discharges or by a continuous activity of increased amplitude that may be subject to spontaneous fluctuations. 2. 2. The development of a hypersensitivity of the respective cortical area to toxins such as Mecholyl or Metrazol could be demonstrated. Mecholyl may accentuate an existing or bring to light a latent assymetry of the spontaneous discharges and/or the tendency to burst discharges. 3. 3. Stimulation of sensory nerves (ulnar, sciatic) is still able to elicit evoked potentials (secondary responses of Forbes) in the sensory cortex deprived of its connections with the ventral posterior thalamic nuclei. On bilateral peripheral stimulation with single shocks, one notices that the secondary response is more pronounced in the sensory area corresponding to the thalamic lesion than in the opposite cortex; this difference becomes more marked under the effect of Mecholyl. 4. 4. These findings may have a bearing upon the development of pain and hyperpathia in cerebral lesions extending into the white matter below the sensory cortex.