Median Raphe Stimulation and Sham Procedures Inhibit the LH Surge

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Abstract
Acute electrolytic stimulation of the median raphe (MR) nucleus (MR Stim) between 1300 and 1600 h on proestrus blocked ovulation in 10 of the 21 rats tested, whereas all sham-treated (MR Sham, no current) animals ovulated normally (n = 12). MR Stim at 1600 h on proestrus in individual cannulated rats turned off the luteinizing hormone (LH) surge in all animals tested. MR Sham treatment also abruptly inhibited the LH surge, although all animals ovulated. Manipulations associated with acute surgical procedures (puncture of the dura mater, ether anesthesia alone) inhibited the LH surge, with the magnitude of LH inhibition directly related to the severity of the operative procedures performed (P < 0.025). Inhibition of ovulation following MR stimulation probably can be attributed to a response to stress qualitatively similar but more severe than that experienced by the MR sham group and inhibitory inputs to the ovulatory LH release mechanism cannot be studied using acute surgical procedures.