Cytisine-induced behavioral activation: delineation of neuroanatomical locus of action.

Systemic injections of nicotine increase locomotor activity. The present study was designed to determine whether there is a circumscribed region in the ventral tegmentum that mediates the locomotor-activating effects of nicotine. The mapping technique was used to delineate this region: bilateral injections of cytisine (1 nmol/0.5 microliters per side) were made into sites in and around the ventral tegmentum and the amount of locomotion associated with each site was quantified. The distribution of injection sites spanned between 0.8 and 4.6 mm posterior to bregma. The amount of locomotion varied with relation to the area into which cytisine was injected and a region was identified within which injections of cytisine preferentially increased locomotion. This region appears to have reasonably well-defined anterior and posterior boundaries. Since a portion of the delineated area overlaps the dopamine-containing cell-body region, the possibility remains that the activation of the mesolimbic dopamine system may contribute to the behavioral activation associated with ventral tegmental injections of cytisine. This same system may contribute to the locomotor-activating effects associated with systemic injections of nicotine.