Dopamine in the Lateral Caudate-Putamen of the Rat Is Essential for Somatosensory Orientation

The present study examined the possible localization of somatosensory orientation in the caudate-putamen (CP) of the rat. In the first experiment, 6-hydroxydopamine (6-OHDA) was injected into either the anterodorsal (AD), anteroventral (AV), posterodorsal (PD), or posteroventral (PV) CP. Only rats with PV-CP 6-OHDA injections showed impaired orientation scores. However, these PV injections often caused widespread CP dopamine (DA) depletions, and no specific CP region appeared to be particularly associated with somatosensory orientation. In the second experiment, multiple injections of 6-OHDA were directed toward the medial or lateral halves of the CP to assess their relative contributions directly. DA depletions confined to the lateral (but not medial) CP resulted in orientation deficits; these deficits were greater than would be predicted from the volume of CP/DA loss. Furthermore, the magnitude of the DA fluorescence loss in the lateral CP was more highly correlated with the orientation impairment than was the medial CP fluorescence loss. Thus the lateral CP contributes to sensorimotor functions to a greater extent than does the medial CP, but the volume of CP/DA depletion also appears important.