Profile of the Ovulatory Surge of LH During Stimulation of Median Raphe Neurons in Conscious, Freely Moving Rats

• Published in: Biology of reproduction Vol. 23; no. 4; pp. 710 - 719
• Main Authors: Barofsky, A L, Harney, J W
• Format: Journal Article
• Language: English
• Published: United States Society for the Study of Reproduction 01.11.1980
• Subjects: Animals; Brain Stem - physiology; Electric Stimulation; Female; Hypothalamus - physiology; Luteinizing Hormone - metabolism; Neurons - physiology; Ovulation; Pregnancy; Proestrus; Raphe Nuclei - physiology; Rats
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1095/biolreprod23.4.710

The present study was designed to test the hypothesis that neurons that project from the median raphe (MR) nucleus to the hypothalamus inhibit the ovulatory surge of LH. Concentric bipolar stainless steel electrodes were stereotaxically implanted in the MR nucleus of female rats, and an intravascular cannula was placed into either the right jugular vein or the abdominal aorta. Individual unanesthetized animals were subjected to the following procedures on successive proestrous (PE) days for as long as the cannula remained patent and cycles followed a regular 4 day sequence. On PE afternoon animals were either 1) Bled Only in the animal quarters, 2) placed into a Plexiglas "stimulation chamber" for a 1 h adaptation period followed by a 1 h Sham stimulation period (equipment activated, no current passed), or 3) stimulated in the MR nucleus (MR Stim) with matched pairs of biphasic 1 msec pulses (10 Hz, 1 mA peak-to-peak, 30 sec on-off for 1 h). Hourly blood samples were collected via the cannula from 1400-2000 h on PE, and plasma LH was measured by radloimmunoassay. Neither the cannulation procedure nor the MR implant altered the time of onset or the profile of the LH surge. However, the sham stimulation procedure, as expected from previous observations, delayed both the onset and peak of the LH surge by 1 h. Stimulation of a circumscribed area in the anterior MR nucleus further delayed and attenuated the LH surge when compared with the profile of LH release following sham stimulation in the same individuals on alternate PE days. The effect of stimulation within an individual was remarkably consistent and dependent upon the precise location of the electrode tip. This study supports the notion that the LH surge mechanism is extremely sensitive to alteration by nonspecific experimental manipulation and suggests that some units in the anterior MR nucleus have the ability to delay the LH surge.