Acute Effect of Neural Deafferentation on Timing of Gonadotropin Secretion Before Proestrus in the Female Rat

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An attempt was made to investigate a role of the brain on release of gonadotropin responsible for the events of proestrus and estrus in the 4-day cyclic rats. Rats were acutely deafferented at the level of anterior commissure (AC) with three kinds of the L-shaped knives at the different time of day, and autopsied to examine the uterine distension and ovulation on the days of expected proestrus or estrus. Serum and pituitary level of LH, FSH and prolactin in the deafferented rats were measured by radioimmunoassay. The results are as follows: 1) With an L-shaped knife of 2.5 mm of the horizontal blade (knife A) the fornix (Fx) and the stria terminalis (ST) were interrupted and simultaneously the tract of diagonal bundle of Broca (TDB), the bed nucleus of stria terminalis (BST), the nucleus of accumbens (ACC), the nucleus of anterior commissure (NAC) and parolfactory area were commonly damaged. The deafferentation at 20:00 on the day of diestrus I prevented vaginal cornification, uterine distension and ovulation on the expected estrous day. Full cornification was observed in all examined rats with transection after 10:00 on the day of diestrus II, while uterine distension was not observed in the rats with transection before 20:00 on the same day. None of rats bearing the transection ovulated on the day of estrus, even the transection was performed at 8:00 on the day of proestrus. 2) With an L-shaped knife of 1.4mm of the horizontal blade (knife B) the Fx were interrupted and the BAC and the TDB were commonly damaged, however, the ST, the BST and the ACC were only partially damaged. Most of results following to the neural transection with knife B were similar to those observed with knife A except for ovulation being observed in the rats transected at 8:00 on the day of proestrus. However, transection at the mid-thalamus (knife placed at 2mm caudal to the AC) did not interfere any normal cyclic changes. 3) Estrogen injection into the rats transected with knife B at 20:00 on the day of diestrus II resulted in inducing ovulation, while with knife A did not. 4) Transection either Fx or medial cortico-hypothalamic tract (CHT) with an L-shaped knife of 1.0 mm of the horizontal blade (knife C) on the day of diestrus I partially prevented the occurrence of events of proestrus and estrus. 5) Transection of the septal complex with knife B at 20:00 on the day of diestrus I prevented a rise of pituitary LH, pituitary prolactin and serum prolactin, which used to be observed in normal proestrus. Both Fx and CHT transection resulted in an increase of pituitary FSH. From the ovariectomy experiment the ovary of the our colonys rats must be in situ at 15:00 for vaginal cornification and at 24:00 for uterine distension. Thus, following facts are suggested 1) the septal complex or higher brain such as the limbic structure may be involved in the release of gonadotropin responsible for the events of proestrus and estrus, 2) timing of release of gonadotropin (folliculotropin) might occur preceding to the ovarian changes and it must start sometime before early morning of diestrus II.
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Acute Effect of Neural Deafferentation on Timing of Gonadotropin Secretion Before Proestrus in the Female Rat

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