Effects of lesion and stimulation of rat hypothalamic arcuate nucleus on the pain system.

Electrolytic lesion and stimulation of the arcuate nucleus of the hypothalamus (ARH) were investigated in Wistar albino rats. 1) Discrete lesion of the ARH is followed by hyperalgesia as manifested by significantly high values of pain rating in the formalin test and by depressed analgesic effect of electroacupuncture stimulation on digastric electromyogram (dEMG) activity. 2) ARH stimulation appreciably suppressed both the responses of neurons in the lateral hypothalamus (LHA) and dEMG activity induced by tooth pulp stimulation. The suppressive influence of ARH stimulation on the responses of LHA neurons was antagonized by intraperitoneally injected and electrophoretically applied naloxone. It is thus suggested that the ARH is involved in induction or modulation of opioid-mediated analgesia.