Blockade of both pilocarpine and amphetamine-induced head-shaking with dopamine receptor antagonists

The range of central dopaminergic mechanisms involved in both d-amphetamine- and pilocarpine-induced head-shaking was studied in 7--9 days old rats by means of two DA antagonists: pimozide and spiroperidol. Both blocking agents exert their effects on H--S following dose-response curves which are similar, whatever the drug used to evoke head-shaking. A complete blocking effect on H--S is reached with pimozide at a dose of 2 mg kg-1; with spiroperidol at 0.1 mg kg-1 (for pilocarpine-induced H--S) and at 0.2 mg kg-1 (for H--S evoked by d-amphetamine). These results, together with those previously reported, suggest that dopaminergic and cholinergic facilitatory influences on H--S seem to be organized in series.