Neurochemical correlates of conditioned circling within localized regions of the striatum

Two experiments were conducted to determine the effects of conditioned circling on the concentrations of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) within discrete regions of the striatum (STR). The first study assessed the inherent regional distributions of these compounds with respect to the three primary axes: anterior-posterior, dorsal-ventral and medial-lateral. Concentrations of DA, DOPAC and HVA and the ratios of each metabolite to DA were found to vary across each dimension. However, the topographical distribution of each compound was unique. The results of the first experiment confirm that the STR is not a homogeneous structure. It is possible that the regional variations in dopamine metabolism underly the diverse functions which the STR is thought to modulate. The second experiment determined whether specific regions of the STR were differentially involved in the mediation of conditioned circling. DA metabolism, as estimated by metabolite concentrations and metabolite to DA ratios, was bilaterally increased within the anterior dorsomedial and dorsolateral STR, relative to noncircling, water-deprived controls. DOPAC and the corresponding ratio were enhanced selectively within the dorsomedial region, whereas HVA and its ratio to DA were increased preferentially within the dorsolateral STR. The ratio of DOPAC to DA was also enhanced within the anterior ventromedial STR. No other significant neurochemical effects were detected. These results support the hypothesis that the dorsal STR critically subserves circling. Moreover, it is possible that the medial and lateral regions of the dorsal STR are differentially involved in circling. These results also confirm previous reports of bilateral augmentation of striatal DA metabolism in association with high rates of conditioned circling.