Unilateral mesolimbicocortical dopamine denervation decreases locomotion in the open field and after amphetamine

Abstract

Unilateral denervation of the mesolimbicocortical dopaminergic (DA) system was produced by microinjections of 6-hydroxydopamine (6-OHDA) into the right or left anterolateral hypothalamus after desmethylimipramine pretreatment. Unilateral DA denervation was confirmed by the marked loss of fluorescent fibers in mesolimbic DA terminal fields in brains processed for catecholamine histofluorescence with the glyoxylic acid-paraformaldehyde method. Such unilateral DA denervation significantly decreased the locomotor exploration of an open field and the locomotor response to d-amphetamine (1.5 mg/kg). These results demonstrate that unilateral mesolimbococortical DA denervation is sufficient, and that bilateral denervation of a single mesolimbic terminal field such as the n. accumbens is not necessary, to produce a decrease in the locomotor response to amphetamine or a decrease of locomotion in the open field. The results are consistent with the hypothesis that the mesolimbicocortical DA system energizes behavior, but does not direct it.