Atropine and naloxone sensitive stimulation produced analgesia from pretectal nucleus in rat

Mild and brief electrical stimulation of sites in the pretectal nucleus (PTN) of rats evoked potent analgesia of long duration, without significant aversions and was unassociated with motor deficit. The present study has analysed effects of opioidergic and cholinergic neurotransmitter antagonists administered intracerebroventricularly (i.c.v.) on this analgesia. Pretreatment either with naloxone or atropine sulphate both in doses of 30 and 50 micrograms each, respectively i.c.v., 10 min prior to subsequent pretectal stimulation, significantly attenuated the increase in tailflick latency. The antagonism of pretectal stimulation produced analgesia (PSPA) by naloxone and atropine, raises the possibility of involvement of both endogenous opioids and cholinergic mechanisms in pretectal analgesia.