Long-term administration of (-)deprenyl (selegiline), a compound which facilitates dopaminergic tone in the brain, leaves the sensitivity of dopamine receptors to apomorphine unchanged.

The effect of repeated administration of the MAO-B enzyme blocker (-)deprenyl on the apomorphine (APO) sensitivity of dopamine (DA) receptors was investigated in rats, and compared to the effect of other drugs influencing the dopaminergic system. APO was given either in a high dose (0.1-0.6 mg/kg), which induces stereotyped behaviour or in a smaller one (0.02 mg/kg) causing sedation. Repeated administration of all the other drugs investigated (except (-)deprenyl), i.e. haloperidol, d-amphetamine, (1 mg/kg s.c., respectively) and the MAO-A blocker clorgyline (0.25 mg/kg s.c.) altered the efficiency of APO on the stereotypy. Haloperidol, clorgyline (0.5 mg/kg s.c.) and imipramine (10 mg/kg i.p.) attenuated the APO-sedation. The long-lasting administration of (-)deprenyl (0.25 mg/kg s.c., daily for 42 days) however, left the effects of APO unchanged, demonstrating that (-)deprenyl facilitates the dopaminergic tone in the rat brain without altering the sensitivity of DA receptors.