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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.
Phillips et al. (Fri,) studied this question.