Suppression of shock elicited target biting by analgesic midbrain stimulation.

Rats with chronic electrodes in or near the central gray (PVG) of the midbrain were tested with a tail pinch to determine analgesic brain stimulation parameters. Then blocks of tail shock, adjusted to a level that produced consistent biting on an inanimate target, were alternated with blocks of tail shock preceded by PVG stimulation. Biting following the tail shock was reduced or eliminated when the brain stimulation preceded the shock. It was concluded that stimulation in the PVG region reduces target biting produced by nociceptive stimulation, probably via an analgesic effect. Also, no biting was associated with brain stimulation, indicating that the bite suppression function is separate from the attack producing function of other central gray areas.