Effect of electrical stimulation of the medial thalamus on neuronal activity of the thalamic ventrobasal complex in the anesthetized cat / 全日本鍼灸学会雑誌

The preceding companion paper reported the influence of stimulation of the centre median nucleus (CM) of the thalamus on neuronal activity in the thalamic ventrobasal complex (VB). In the present study, a modification of the medial thalamus (MTh) except for the CM on activity in the somatosensory relay neurons of the thalamus was investigated in the cat. Extracellular multi-unitary discharges were recorded simultaneously from the VB using the multimicroelectrode system. The effects of MTh stimulation with a pulse train on VB neuronal activity were examined. The response of VB neuron to stimulation of other MTh nuclei were classified into the same four classes as that for CM stimulation : inhibited and then excited type; excited type; inhibited type; and non-responsive type. All four types of responses were observed in several nuclei of the MTh, such as the CM, central lateral nucleus (CL), mediodorsal nucleus (MD) and ventral posterior medial nucleus (VPM). MTh stimulation was more effective in nociceptive neurons than in non-nociceptive neurons. However, the effect of MTh stimulation differed among simultaneously recorded nociceptive neurons even when their receptive fields and recording sites were in close proximity. In some VB neurons, the response to stimulation applied to the center of the receptive field was also suppressed by MTh stimulation. Furthermore, an inhibitory effect on the response to stimulation applied to the periphery of the receptive field was observed even when the response to stimulation applied to the center of the receptive field was not inhibited by MTh stimulation. Thus, a large component of the MTh can modify VB neuronal activity and may be involved in the somatosensory system through complex mechanisms.

Effect of electrical stimulation of the centre median nucleus on neuronal activity of the thalamic ventrobasal complex in the anesthetized cat / 全日本鍼灸学会雑誌

Involvement of the centre médian nucleus (CM) of the thalamus in the central mechanisms of somatosensory system including pain sensation was investigated in the anesthetized cat. Extracellular multi-unitary discharges were recorded simultaneously from the thalamic ventrobasal complex (VB) using the multimicroelectrode system. The effects of CM stimuli with single shocks and pulse train on VB neuronal activities were examined. The VB neurons were characterized according to their responsiveness to mechanical stimuli, and then classified into nociceptive and non-nociceptive neurons. The effects of pulse train stimulation were more pronounced than those of single shocks. Of 86 units tested, the effects of pulse train CM stimulation were observed in 45 units including 31 nociceptive and 14 non-nociceptive units. The VB neurons were divided into four classes according to the response types to pulse train CM stimulation. Of the 86 units, 20 were classified as class 1 which exhibited inhibition of spontaneous discharges followed by excitation. Thirteen units were class 2 which exhibited only excitation, and 12 were class 3 which showed only inhibition of spontaneous discharges. The remaining 41 units were class 4 which did not respond to CM stimulation. Differences in response to CM stimulation were observed among simultaneously recorded units even when the receptive fields and recording sites were in close proximity. Response to single shocks with a short latency of approximately 1.5 ms was observed in several VB neurons. Further inhibitory effects of pulse train CM stimulation on discharges evoked by stimulation of the receptive field were also observed.<BR>Thus, the CM appears to modify neuronal activities in the VB. However, the CM exerts not only an inhibitory effect but also excitatory on the VB neuronal activities. The effects are also observed on non-nociceptive units in the VB.

Ascending pathways of skin and deep information projecting to the ventral posterior lateral nucleus of thalamus in the cat / 全日本鍼灸学会雑誌

In acupuncture, the typical sensation induced by insertion of a needle into the muscle that called “De Qi” is essential to induce acupuncture analgesia. The effect of acupuncture analgesia may depend on the deep afferents rather than to the cutaneous ones at the acupuncture point. The ascending pathways conveying these skin and deep afferents project to the ventral posterior lateral nucleus (VPL) of thalamus, one of the thalamic relay nuclei projected to the cerebral cortex, were examined by spinal cord lesion at the cervical level with observation of the responses evoked by electrical stimulation applied selectively to the skin and deep tissues.<BR>Neuronal discharges were recorded extracellularly from the VPL using the multimicroelectrode technique. After spontaneous neuronal activities were recorded, the receptive fields and characteristics were determined by applying some kinds of mechanical stimulation to the receptive field. The skin and deep structures were then selectively stimulated using a pair of stainless steel needles and insulated needles except for tips. Units were classified for skin units, deep units, and skin-deep units according to the responses to the electrical stimulation. Responses were elicited in some neurons following to both skin and deep stimuli. The latency of response elicited by electrical stimulation applied to the deep structure was slightly shorter than that of the skin structure. The recording sites for deep units were located more rostrally in the dorsal region of the VPL than that for the skin units.<BR>The afferents of some skin-deep neurons from both skin and deep structures were ascended through different pathways in the spinal cord. The skin and deep afferents were found to converge at the thalamic level.

Ascending pathways mediating cardiovascular signals to the ventral posterior lateral nucleus of thalamus in the cat / 全日本鍼灸学会雑誌

Neuronal activities in the ventral posterior lateral nucleus (VPL) of the cat thalamus were recorded extracellularly using the multimicroelectrode system. In spontaneous activities, some neurons received information from structures related to cardiovascular movement and also from peripheral somatic receptive fields (Rfs). These unitary activities were synchronized with heart beat, therefore they are called as heart beat (HB) discharges. This phenomenon may be concerned with referred pain. Thus, some VPL neurons appear to relay cardiovascular information to the cerebral cortex. The characteristics of 39 HB units were determined by mechanical stimulation such as bending hair, tapping, pinching and joint movement. To investigate the ascending pathways, transection of vagi and partial spinal cord lesions at the cervical level were performed. HB activities were unaffected by bilateral vagotomy. Some of the HB activities disappeared following partial cordotomy of the lateral portion of the ventrolateral funiculus ipsilateral to the receptive field. However, evoked responses to electrical stimulation applied to the HB Rfs persisted. After the remaining cord was severed, the evoked responses vanished. These results show that afferent signals of HB activities and evoked responses to electrical stimulation appear to ascend through different pathways and converge at the thalamic level.