ELECTROPHYSIOLOGICAL VERIFICATION OF THE PRESENCE OF D-1 AND D-2 DOPAMINE-RECEPTORS WITHIN THE VENTRAL PALLIDUM

The ventral pallidum is a basal forebrain region recently shown to rec eive dopaminergic projections from the midbrain. Binding sites for the D1 and D2 dopamine receptor families have been identified within the ventral pallidum, yet the consequences of activating these receptors h ave not been studied. Thus, to characterize the physiological pharmaco logy of D1 and D2 receptor subtypes for the ventral pallidum, extracel lular single-neuron recording and microiontophoretic techniques were u sed in chloral hydrate-anesthetized rats. Half of the 93 ventral palli dal neurons tested were sensitive to iontophoresis of dopamine (DA), a nd both rate increases and decreases were observed. Co-iontophoresis o f either the D1 antagonist SCH23390, or the D2 antagonist sulpiride, g enerally attenuated the DA-induced rate changes. Like DA, about half o f the ventral pallidal neurons tested were sensitive to the D1 agonist , SKF38393. Yet in contrast to DA, rate suppression was observed almos t exclusively, and the magnitude of this decrease was greater than tha t produced by DA. SKF38393-induced suppressions were antagonized by SC H23390, but not by sulpiride, demonstrating the specificity of the D1 agonist. Most of the neurons tested were not affected by quinpirole, b ut when responsive to the D2 agonist, rate increases were observed mos t often. The increases were antagonized by the D2 antagonist sulpiride , but not SCH23390, demonstrating that this response resulted from an activation of D2 receptors. These results support binding studies demo nstrating that both D1 and D2 receptors are present in the ventral pal lidum, and reveal that the independent activation of each of these is sufficient to alter neuronal activity. (C) 1994 Wiley-Liss, Inc.