The effect of pre- and postoperative procedures on physostigmine- and apomorphine-induced yawning in rats

Previous experiments have shown that the potentiation of physostigmine-induced yawning by nifedipine is abolished by sham-lesioning procedures in rats, whereas the nifedipine potentiation of apomorphine-induced yawning is unaffected. The present results demonstrate that either the presurgical drug treatment (desmethylimipramine and pentobarbital) or 7 days isolation was alone sufficient to reduce the yawning response to physostigmine and abolish its potentiation by nifedipine. The sham-lesioned rats responded normally to a combination of apomorphine and nifedipine. These results suggest that the stress associated with standard operative procedures can differentially affect drug interactions with yawning induced by either apomorphine or physostigmine and that caution should be exercised when interpreting results from animals that have been similarly stressed.