ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
A total of 681 unitary activities were recorded extracellularly in the thalamic ventrobasal complex (VB) of anesthetized and immobilized cats, of which 67 units were synchronized with heart beat (HB) with some relative latency. HB discharges were divided into six types according to the shape in their post Rwave time histogram (PRTH) analysis, however some HB changed in both the number and relative latency of the discharge, and were identified their receptive fields (Rfs) on or in the bodies, of 35 units of the 681 (5.1%). These HB Rfs were distributed widely from the tip of auricula to the toe of hindlimb. The lateralities of their HB Rfs were all contralateral to recording sites in the thalamic VB. In general, the HB Rfs of the thalamic VB were distributed on upper half of the bodies much more than the lower half; especially on the upper cervix, the chest and the forelimbs. The somatotopic organization of HB units in thalamic VB showed the same tendency. The relative latencies between the R-wave of ECG and HB activities showed the tendency to be dependent on the distances from the Rfs to the recording sites in thalamic VB. Some HB activity was followed by a silent period when the background activities disappeared during several tens of milliseconds which was presumably caused by a feedback inhibitory mechanism consisting of the axon collateral of the thalamocortical cell and the inhibitory interneuron.
ABSTRACT
Peripheral mechanisms that induce analgesic effects in manual acupuncture were studied in urethane-anesthetized rats. Unitary extracellular recordings were made from spinal wide dynamic range (WDR) neurons and repetitive electrical stimuli were delivered to the excitatory receptive fields to determine a noxious index. First, the analgesic effects of manual acupuncture and a noxious pinch to the skin (Diffuse Noxious Inhibitory Controls: DNIC) were compared. Second, manual acupuncture was applied to different structures at the acupuncture point, such as the skin, skin plus muscle, and muscle. In a third experiment, the analgesic effects of intramuscular injection of 4.5% NaCl and manual acupuncuture were compared. Manual acupuncture and a noxious pinch exhibited a very similar time course and magnitude of inhibitory effects on C-evoked discharges. As for differential stimulation of the acupuncture point, application of the needle to the skin only was less effective than to the skin plus muscle or the muscle only. Both intramuscular injection of 4.5% NaCl and manual acupuncture reduced C-evoked discharges while injection of isotonic saline produced almost no inhibitory effects. These data suggest that application of manual acupuncture might arouse noxious sensations that result in activating pain inhibitory processes. Moreover, it is thought that excitation of polymodal receptors in the muscle is a critical factor in inducing analgesic effects in manual acupuncture.
ABSTRACT
Manual acupuncture to ST 36 Zusanli induces both long-lasting and short-term inhibitory effects on C-evoked discharges of wide dynamic range (WDR) neurons in the lumbar cord. The possible involvement of the central nervous system in producing these two types of inhibitions was investigated in urethane-anesthetized rats. In one expriment, the existence of a descending pain inhibitory system was studied using spinal conduction blocks at the cervical level. In a separate experiment, naloxone was administered systemically to investigate the participation of endogenous opioids.<br>Long-lasting inhibition was found to be due to a descending pain inhibitory system from the upper central nervous system together with the involvement of an opioidergic link. On the other hand, short-term inhibition was attributed to a propriospinal pain inhibitory system and endogenous opioids were not implicated.
ABSTRACT
In 1987, Yamamoto developed Initial Skin Temperature Controlled Repeated Thermal Stimulation System (STRTS), consisting of microcomputer PC-9801 (NEC Co.) and the pain meter NYT-55 (KUDO ELECTRIC Co.) which was modified type of Hardy's algometer. We used STRTS to establish more simple and accurate evaluation of the effects of electroacupuncture (EA).<br>Five female volunteer subjects with mean age of 21.8 were involved in this measurement. Radiant heat stimuli of 200mcal/sec/cm<sup>2</sup> were repeatedly delivered to six different skin areas on the left body surface where blackened sticky tape were applied. Stainless acupuncture needles were inserted into LI4 Hegu _??__??_ until subjects felt a typical sensation called De Qi. Both Hegu were stimulated electrically with 4 and 10Hz for 30 minutes. We measured pain threshold repeatedly before and after an EA with the passage of time.<br>EA generally raised pain threshold of measuring points, especially the neck and forehead. In some cases, however, pain thresholds of several points were reduced by EA. These results suggested that effects of EA varied with the subjects. As for frequency of EA, 4Hz was much effective than that of 10Hz.