Influences of Hypothalamic Deafferentation on Pituitary FSH Release and Estrogen Feedback in Immature Female Parabiotic Rats

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Abstract
The hypothalamus was deafferented by Halász-knife cuts at two different levels in 23-day-old female rats The anterior frontal cut (AFC) along the caudal border of the optic chiasma severed the rostro-dorsal connections of the hypothalamus but left intact the anatomical links of the anterior hypothalamic area (AHA) with more posterior hypothalamic structures. The posterior frontal cut (PFC) behind the AHA interrupted its posterior connections with the rest of the hypothalamus. The rats were ovatiectomized on day 24 and joined in parabiosis with intact females of the same age on day 28. Daily injections of oil or estrogen to ovariectomized partners were started immediately following parabiosis and continued until autopsy on day 34. FSH activity was assessed by the augmentation of the ovarian response to HCG (20 IU/day) injected into intact partners during the last 3 days of the experiment. In the oil-treatment (non-estrogen) experiments, a significant decrease in ovarian weight was found in the PFC group when compared with sham-operated controls; however, no difference was observed in the AFC group. Small doses of estrogen (0.5 µg/day) that were ineffective in sham-operated controls produced a significant decrease in ovarian weight in the AFC group. Higher doses of estrogen (1 µg/day), however, were effective in reducing ovarian weight in both controls and AFC pairs. The results suggest that the separation of AHA from its posterior connections prevents the post-castration rise of FSH in the serum, whereas interruption of rostrodorsal connections of AHA allows the normal post-castration increase of FSH. However, anterior deafferentation of the hypothalamus appears to result in increased sensitivity to estrogen.

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