Blockade of dopamine D2, but not of D1 receptors in the rat globus pallidus induced Fos-like immunoreactivity in the caudate-putamen, substantia nigra and entopeduncular nucleus.

In the present study, we investigated Fos-like immunoreactivity (FLI) evoked by pallidal dopamine (DA) D1 and D2 receptor blockade in the caudate-putamen (CPu), substantia nigra (SN) and entopeduncular nucleus (EP), i.e. major target areas of pallidal efferents. Results demonstrate that infusion of the selective D1 antagonist SCH23390 (1 and 4 microg/0.5 microl) into the globus pallidus (GP) did not induce FLI in the CPu, SN and EP. In contrast, intrapallidal infusion of a low dose of the selective D2 antagonist S(-)-sulpiride (15 microg/0.5 microl) induced FLI restricted to the CPu. A higher dose of intrapallidal S(-)-sulpiride (25 microg/0.5 microl) induced FLI in the CPu as well as in the SN and EP. These findings add further evidence to notion that the GP plays a central role in the basal ganglia circuitry and demonstrate an involvement of extrastriatal DA via D2 receptors.