Medial dorsal striatum is more sensitive than lateral dorsal striatum to cocaine inhibition of exogenous dopamine clearance: relation to [3H]mazindol binding, but not striosome/matrix.
Previous studies have shown that acute systemic cocaine inhibits dopamine (DA) transport and thereby produces dose-dependent changes in exogenous DA clearance in the brain. This measure reflects the dynamic activity of the DA transporter. There are also differential effects of cocaine on DA clearance in dorsal and ventral striatum, and evidence from many studies suggests that even within the dorsal striatum, the interaction of cocaine with the DA transporter may not be homogeneous. A greater understanding of how cocaine interacts with the striatal DA transporter will help clarify the role of the striatum in mediating effects of cocaine. In these studies we used in vivo electrochemical recording to examine the effect of ip cocaine on exogenous DA clearance in the medial and lateral dorsal striatum with respect to both DA transporter binding sites and electrode localization to striosomes or matrix. Baseline exogenous DA clearance was different in medial and lateral dorsal striatum in the absence of cocaine. Systemic cocaine produced a more pronounced inhibition of DA clearance in medial dorsal striatum than in lateral dorsal striatum. [3H]Mazindol binding to DA transporters was lower in medial dorsal striatum, but was not in register with striosome or matrix compartments. There was no notable difference between cocaine's effects on DA clearance in striosome or matrix that was due to this compartmentalization. Others have demonstrated that medial dorsal striatum receives proportionally more innervation from the mesolimbic, as opposed to the nigrostriatal, DA system. Taken together, these and previous in vivo results suggest that this differential sensitivity to cocaine reflects the unique properties of the ascending mesolimbic DA projection and the lower density of DA transporters associated with it.