Inhibition of visceral pain by electrical stimulation of the periaqueductal gray matter.

Numerous recent studies demonstrated that electrical stimulation of the periaqueductal gray matter (PGM) can result in powerful analgesia to pain of somatic origin. In the present study, we have developed a visceral pain test employing intraperitoneal injection of hypertonic saline which yields a writhing response in the adult rat more reliably than other pain-producing substances. With this test we show that writhing as well as the response to radiant heat (tail flick test) are completely inhibited in all animals with PGM electrode placements.