Sexual behavior and neural degeneration following hypothalamic knife cuts

Abstract

Frontal (FC), frontal lateral (FLC) or sham deafferentations were performed on adult ovariectomized (OVX) female rats. Cuts were produced retrochiasmatically with a modified Halasz knife equipped with an extrudable blade (1.5 mm radius). At 60 days after surgery each animal was tested for lordosis behavior (LQ) following either 3 daily injections of estradiol benzoate (EB) alone or with progesterone (P). Male sex behavior was tested 5 times at 4 day intervals during a 21 day regime of daily treatment with testosterone propionate. Additional FC and FLC rats were sacrificed at 10 and 14 days after surgery and degeneration patterns were studied using the Fink-Heimer method. Brains were removed and prepared for histological examination of cut location and dimensions in each rat. Behavioral effects of knife cuts were analyzed by 2 methods: (1) grouping based on common areas of glial scars; (2) a multiple regression analysis of cut morphometrics with sex behavior. No group differences were found when LQ of FC and FLC rats were compared with Sham animals after EB alone. The expected increase in LQ which follows EB and P treatment was not observed in FLC rats when means were compared. In male sex behavior tests FC and FLC groups showed more total mounts than Sham rats, however, the differences were not statistically significant. Multiple regression analysis of individual cut location and width with behavior indicated that more anterior and lateral the cut location (FC and FLC) the greater the decrement in female sex behavior. Fink-Heimer studies revealed that both FC and FLC cuts produced degeneration bilaterally in the stria medullares, habenula, fasciculus retroflexus, in addition to arcuate, ventromedial and periventricular hypothalamic nuclei. FLC cuts also resulted in bilateral degeneration in the zona incerta, the cerebral peduncles and in the medial forebrain bundle. Collectively these data indicate the complete interruption of anterior and lateral connections of the anterior hypothalamic area and mediobasal hypothalamus with the remainder of the brain in the female rat reduced lordosis behavior.