Dopamine and 7-OH-DPAT may act on D-3 receptors to inhibit tuberoinfundibular dopaminergic neurons

Whether the tuberoinfundibular dopaminergic (TIDA) neurons resided in the d orsomedial arcuate nucleus (dmARN) can respond to dopamine and a dopamine D -3 receptor agonist, 7-hydroxydipropylaminotetralin (7-OH-DPAT), was the fo cus of this study. In studies using extracellular single-unit recording of dmARN neurons in brain slices obtained from ovariectomized rats, dopamine a nd 7-OH-DPAT inhibited 60.1% (n = 141) and 80.9% (n = 47) of recorded dmARN neurons, respectively. Other dopamine D-1 or D-2 receptor agonists were no t as effective. Intracerebroventricular injection of 7-OH-DPAT (10(-9) mol/ 3 mu l) in ovariectomized, estrogen-primed rats significantly lowered the T IDA neuronal activity as determined by 3,4-dihydroxyphenylacetic acid (DOPA C) levels in the median eminence. Go-administration of a putative D-3 recep tor 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 mu l) into the right dmARN exhibited the same inhibitory effect on TIDA neuron s. In all, dopamine may act on D-3 receptors to exhibit an inhibitory effec t on its own release from the TIDA neurons. (C) 2000 Elsevier Science Inc.