Locomotor activity and a conditioned fear response: correlation with cortical and subcortical binding of the dopamine D1 receptor antagonist.

Rat behavior in the open field and conditioned fear response test was correlated with specific binding of dopamine D1 receptor antagonist [3H]SCH 23390 within different brain structures assayed with autoradiography. A significant positive correlation was found between the ligand binding in the substantia nigra pars reticulata and both animal motor activity (r = 0.67, p < 0.05) and the number of entries into the central sector of the open field (r = 0.59, p < 0.05). On the other hand, rat motility and the central entries were negatively correlated with [3H]SCH 23390 binding within the caudate putamen (r = -0.64, p < 0.05 and r = -0.61 p <0.05, respectively). No correlation was revealed between the ligand binding in the examined brain areas and freezing reaction in the contextual fear conditioning test. The present data indicate for the first time a significant, structure-dependent correlation between rat motor behavior and the dopamine D1 receptor ligand binding within the nigrostriatal system.