ENHANCEMENT OF D(2) RECEPTOR AGONIST-INDUCED INHIBITION BY D(1) RECEPTOR AGONIST IN THE VENTRAL TEGMENTAL AREA

1 A microiontophoretic study was performed on chloral hydrate-anaesthe tized rats to examine the role of D1 receptors in the ventral tegmenta l area (VTA) neurones, which are inhibited by autoreceptor and D2 rece ptor agonists. 2 Inhibition by microiontophoretic application of quinp irole (a D2 agonist) of antidromic spikes elicited by stimulation of t he nucleus accumbens in dopaminergic neurones of the VTA, was signific antly enhanced by simultaneous application of SKF 38393 (D1 agonist), although SKF 38393 alone had little effect on the neurones. 3 In addit ion, quinpirole-induced inhibition was antagonized by iontophoretic ap plication of domperidone (D2 antagonist), but was not affected by SCH 23390 (D1 antagonist). 4 Furthermore, SKF 38393-induced enhancement of inhibition by quinpirole was antagonized by simultaneous application of SCH 23390. 5 These results suggest that activation of D1 receptors located on the VTA dopaminergic neurones or on non-dopaminergic nerve terminals is not essential for inducing inhibition of the dopaminergic neurones, but enhances D2 receptor-mediated inhibition directly or in directly via inhibitory neurones.