Naloxone reversal of morphine catationia: role of caudate and periaqueductal gray.

The narcotic antagonist, naloxone, was microinjected into the head of the caudate nucleus (HC), periaqueductal gray matter (PG), and cerebellar white matter (CB) of rats to counteract the catatonia induced by systemic morphine. Naloxone produced a loss of the catatonic response when administered into HC or PG, but not when microinjected into CB. Isotonic saline in HC, PG, and CB did not counteract the catatonic effects of morphine. The reversal of catatonia was similar for naloxone injections in HC and PG. Both these areas have high concentrations of opiate receptors while CB has few opiate receptors. It is suggested that the HC and PG are involved in the reversal of the catatonic effects of morphine via the high concentrations of opiate receptors found there.