LATERAL HYPOTHALAMUS - SITE INVOLVED IN PAIN MODULATION

The present study is an attempt to examine the neuronal circuitry of a supraspinal site engaged in pain modulation. Five physiological measu res were postulated as the criteria for defining a central nervous sys tem site engaged in the circuitry of pain modulation. The lateral hypo thalamus met these five measures: (i) 81% of the lateral hypothalamus neurons (247/304) responded to noxious stimuli using a single cell rec ording procedure; (ii) stimulation of the periaqueductal gray-dorsal r aphe area or the habenula modulated 98% and 87% of the lateral hypotha lamus noxious-evoked activity; (iii) microiontophoretically applied mo rphine modulated 77% of the lateral hypothalamus noxious evoked activi ty; (iv) electrical stimulation of the lateral hypothalamus produced b ehavioral analgesia proportional to the stimulus intensity as assessed by the tail flick assay; and (v) morphine application into the latera l hypothalamus produced behavioral analgesia in a dose-response manner using, the tail flick assay. In conclusion, the lateral hypothalamus can be considered one of the pain modulation sites.