Electrophysiological Evidence for a Key Control Function of the Medial Preoptic Area in the Regulation of Prolactin Secretion in Cycling, Pregnant and Lactating Rats

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Abstract
Female rats were chronically fitted with stainless steel electrodes in the medial preoptic area (MPOA), together with a chronic atrial blood sampling/blood transfusion catheter. The surgery did not affect cyclicity, pregnancy or lactation. Twenty-five minutes of bilateral electrical stimulation (100-Hz voltage pulses, 0.2 ms width, 10 s on/5 s off) of the MPOA significantly reduced the magnitude of the proestrous and estrous afternoon levels of prolactin (Prl) in cycling rats, the nocturnal and diurnal levels of Prl in pregnant rats as well as Prl secretion during suckling in lactating rats. These data demonstrate that the MPO exerts dominant inhibitory control over all known surges of Prl secretion in female rats and may be considered as ‘antisurge key control center’ for Prl secretion. A functional role of the sexually dimorphic nucleus in the control of Prl secretion is suggested.