Antagonism of the apomorphine-induced yawning by "atypical" neuroleptics.

In relatively small doses, the four "atypical" neuroleptics, sulpiride, clozapine, thoiridazine and mezilamine were effective antagonists of apomorphine-induced yawning in rats. Of the four drugs, used in doses which inhibited apomorphine-induced yawning almost completely, only clozapine also antagonized yawning induced by physostigmine. Therefore it appears that the antagonism of this effect of apomorphine, already reported for classical neuroleptic agents, is also shown by "atypical" ones. By combining apomorphine- and physostigmine-induced yawning, it is possible to assess the anticholinergic component in the antagonism of this effect of apomorphine and this may be of value for the understanding of the mechanisms underlying the "atypical" character.