Desipramine induces yawning behaviour in rats.

Yawning behaviour in rats injected subcutaneously with antidepressant drugs was studied by direct observation. Desipramine (0.1-30 mg/kg) elicited yawning that began 15-20 min after injection and lasted for 60 min, and the dose-response curve showed a bell-shaped form. Desipramine (10 mg/kg) elicited the maximal effect (mean number of yawns 13.6). Haloperidol (0.02 mg/kg), spiperone (0.2 mg/kg), pimozide (4 mg/kg), reserpine (7.5 mg/kg), alpha-methyl-p-tyrosine (250 mg/kg) and scopolamine (0.5 mg/kg) markedly reduced yawning induced by desipramine, whereas prazosin (1 mg/kg) and phenoxybenzamine (5 mg/kg) were without effect. These findings indicate that desipramine induces yawning by a dopaminergic mechanism, and that endogenous dopamine (DA) is necessary for its occurrence. Yawning was observed also after administration of imipramine, clomipramine, trazodone, its metabolite m-chlorophenylpiperazine and (+/-)sulpiride. These drugs given in a similar dose-range to desipramine produced a weaker effect than desipramine. Selective and potent inhibitors of the uptake of noradrenaline (NA) or 5-hydroxytryptamine (5-HT), (+)oxaprotiline and citalopram, did not elicit yawning. A possibility is considered that certain antidepressant drugs induced yawning through an influence on dopaminergic system.