Dopaminergic and noradrenergic substrates of positive reinforcement: differential effects of d- and l-amphetamine.

Intracranial self-stimulation was elicited from electrodes located in either the lateral hypothalamus or substantia nigra of the rat. Facilitatory effects of d- and l-isomers of amphetamine on self-stimulation were assessed. The d-isomer was seven to ten times more effective than the l-isomer at the hypothalamic placement, whereas the two isomers were equipotent for substantia nigra electrodes. These data support the hypothesis that both dopaminergic and noradrenergic systems subserve positive reinforcement.