The Role of the Dorsomedial-Ventromedial Area of the Hypothalamus in the Control of Prolactin Secretion Induced by Cervical Stimulation*

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Abstract
Cervical stimulation (CS) initiates daily nocturnal (N) and diurnal (D) surges of PRL, which persist for at least 10 days, in intact and ovariectomized (OVX) rats. To affect pituitary PRL release, CS probably acts through several areas of the hypothalamus. PRL regulation by one hypothalamic area, the dorsomedial-ventromedial nuclei (DMN-VMN), was investigated in the present study. Electrical stimulation of the DMNVMN of rats with intact ovaries produces both N and D PRL surges of the same magnitude, timing, and persistence as those initiated by CS. However, in long term OVX rats, stimulation of the DMN-VMN results in N surges which last only until day 6 and D surges present only through day 2. OVX rats receiving sc Silastic implants containing progesterone on the day after DMNVMN stimulation had larger N surges, which persisted only as long as those secreted by long term OVX untreated rats. The D surge was unaffected. Rats OVX immediately after DMN-VMN stimulation secreted N surges through day 10, but D surges only through day 6. CS of long term OVX rats bearing lesions or sham lesions within the DMN-VMN results in N surges persisting through day 10. However, D surges could not be initiated by CS in rats bearing DMN-VMN lesions. These results suggest that the DMN-VMN is one area which responds to CS by initiating N and D surges of PRL. Excitation of this area is a requirement for the initiation of D, but not N, surges of PRL. However, continuation of the N surge probably involves the excitation of other areas within the central nervous system.