Dopamine and 7-OH-DPAT may act on D₃ receptors to inhibit tuberoinfundibular dopaminergic neurons

Whether the tuberoinfundibular dopaminergic (TIDA) neurons resided in the dorsomedial arcuate nucleus (dmARN) can respond to dopamine and a dopamine D₃ receptor agonist, 7-hydroxydipropylaminotetralin (7-OH-DPAT), was the focus of this study. In studies using extracellular single-unit recording of dmARN neurons in brain slices obtained from ovariectomized rats, dopamine and 7-OH-DPAT inhibited 60.1% (n = 141) and 80.9% (n = 47) of recorded dmARN neurons, respectively. Other dopamine D₁ or D₂ receptor agonists were not as effective. Intracerebroventricular injection of 7-OH- DPAT (10^-9 mol/3 μl) in ovariectomized, estrogen-primed rats significantly lowered the TIDA neuronal activity as determined by 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the median eminence. Co-administration of a putative D₃ receptor antagonist, U-99194A, could prevent the effect of 7-OH-DPAT. Unilateral microinjection of 7-OH-DPAT or dopamine itself (10^-11-10^-9 mol/0.2 μl) into the right dmARN exhibited the same inhibitory effect on TIDA neurons. In all, dopamine may act on D₃ receptors to exhibit an inhibitory effect on its own release from the TIDA neurons. (C) 2000 Elsevier Science Inc.