Effect of monoamine antagonists on pretectal evoked analgesia in rat

Mild and brief electrical stimulation of sites in the pretectal nucleus of rat produced analgesia (SPA) of long duration without significant aversion. Intracerebroventricular (icv) administration of 5-HT receptor antagonists methysergide (50 micrograms) and ketanserin (50 micrograms) and the dopaminergic antagonist haloperidol (50 micrograms) had no significant effect on pretectal SPA, but alpha and beta adrenoceptor antagonists phenoxybenzamine (50 micrograms) and sotalol (50 micrograms) on icv injection significantly antagonised the pretectal SPA. The results suggest that pretectal SPA involves activation of central adrenoceptors.