Effects of hypothalamic deafferentation on hormonal facilitation of lordosis in ovariectomized rats

Lordosis response in estradiol benzoate (EB)-progesterone (P) primed castrated female rats was studied after 4 types of deafferentation of the medial hypothalamus. Tests were started 4-5 weeks after the brain surgery and ovariectomy. Anterior deafferentation (half-dome cut) at the level behind the suprachiasmatic nucleus (AD-I) and island isolation of the medial basal hypothalamus (MBH island) were highly effective to suppress lordosis response in EB-P primed females. However, the cuts placed dorsal (AD-II) or posterior (AD-III) to the AD-I were without apparent suppressive effect on the EB-P induced display of lordosis. These results suggest that the anterolateral fiber connection with the MBH may participate in lordosis facilitatory mechanisms in EB-P primed females. When reserpine (R) was injected instead of P to EB-primed rats, R effectively facilitated lordosis response in rats with or without the deafferentation (AD-I or MBH island). This suggests that the MBH is not necessary to facilitate lordosis in EB-R primed rats. The site of action of R in the central nervous system for facilitating lordosis may not be the same as that of P.