Long-lasting cardiovascular depression induced by acupuncture-like stimulation of the sciatic nerve in unanaesthetized spontaneously hypertensive rats.

The influence of a prolonged low frequency electrical stimulation of the somatic afferents on cardiovascular and sympathetic nerve activities was investigated in unanaesthetized spontaneously hypertensive rats (SHRs) and Wistar-Kyoto normotensive rats (WKRs). In SHR, an elevation of blood pressure, heart rate and splanchnic nerve outflow was elicited during a 30-min period of sciatic nerve stimulation. Following the cessation of the stimulation, depressor response and bradycardia slowly developed and lasted up to 12 h. Activation of the group III or A-delta afferent fibers was essential for this post-stimulatory response. The progressive depressor response and a parallelled reduction of the splanchnic nerve activity, reached their maxima at about 1 h after the termination of the sciatic stimulation. The magnitude of the post-stimulatory depressor response was correlated with the prestimulatory control blood pressure level. There were also behavioural changes accompanying the depressor response. The cardiovascular and the behavioural depression were immediately reversed by naloxone (10-15 mg/kg, i.v.). The post-stimulatory depressor response was still present after bilateral sino-aortic denervation, but was absent in animals anaesthetized with chloralose and urethane. Emotional stress produced by air-blowing on the animal resulted in pressor response and tachycardia during the period of the stressful stimulation, but there was no depressor response following the termination of air-blowing. These findings indicate a sympathetic and cardiovascular depression induced by a prolonged stimulation of the somatic group III or A-delta afferent fibers; its long duration and naloxone reversibility suggest the involvement of endorphins in the mechanism of this response. The physiological significance of the effects of the prolonged somatic afferent stimulation and its possible relations with acupuncture are discussed.

Sympathetic nervous system involvement in the lateral hypothalamic lesion syndrome.

The role of the sympathetic nervous system in the lateral hypothalamic syndrome of body-weight loss was investigated. Bilateral electrolytic lesions of the lateral hypothalamus (LH) were performed in 90-day-old male albino rats. In experiment 1, the splanchnic nerves were resected at 35 days (right) and 70 days (left) postlesion. In experiment 2, bilateral adrenal demedullations were performed in a second group of rats with LH lesions (LH rats) at 35 days postlesion. The results indicated that lesions of the lateral hypothalamic area lowered body-weight maintenance levels to approximately 87% of nonlesion control values. Bilateral splanchnicetomy produced a significantly greater body-weight loss in nonlesion animals than in LH rats. Following adrenal demedullation, nonlesion rats also reduced body-weight levels whereas LH rats significantly increased weight-maintenance levels. In addition, the adrenal glands of LH rats with sham demedullations weighed significantly more than the adrenals of nonlesion-sham demedullated animals. These data are discussed in relation to metabolic-autonomic mechanisms that may play a role in LH lesion-induced weight loss.