Effects of -methyl-p-tyrosine and L-DOPA on brain self-stimulation and motor activity in rats.

Rats with electrodes implanted in the posterior lateral hypothalamus and ventromedial tegmentum were trained to self-stimulate. Animals were treated (i.p.) first with alpha-methyl-p-tyrosine (alpha-MPT) and then L-DOPA; their self-stimulation rates and spontaneous behaviour were recorded. alpha-MPT (100 mg/kg) had an immediate and long lasting suppressive effect on self-stimulation, within the first half hour. L-DOPA administration failed to reinstate self-stimulation. Hypoactivity also followed alpha-MPT injections. While the behavioural changes were minimal after L-DOPA 50 mg/kg, a decrease of spontaneous activity and moderate hyper-reactivity were observed following L-DOPA at a dose of 200 mg/kg. Theoretical implications are discussed.