Reduced ovarian function and lordosis behavior following hypothalamic knife cuts

Abstract

Lordosis behavior (LQ) estrous cycles and ovarian status were studied in the same animals following either frontal (FC), frontolateral (FLC) or sham (S) surgical interruption of medial basal hypothalamic (MBH) neural connections made with a modified Halász knife (1.5 mm radius). LQ was studied in adult female rats at 7, 30, 105 and 180 day after FC, FLC or S and estrous cycles were monitored for 28 day after cuts. Vaginal cytology examined before and after S surgery indicated regular 4–5 day cycles, whereas after FC vaginal cytology became predominately cornified and after FLC it was variable. Ovarian weights and appearance at ovariectomy (OVX) supported cycle data: S ovaries had recent corpora lutea (CL); FC gonads were smaller with no recent CL and FLC gonads appeared atrophie. Multiple regression analysis of individual FC and FLC dimensions indicated that cut location and dimensions contributed significantly to the length of postoperative estrus periods. After OVX all animals were tested for LQ after estradiol benzoate (EB) and EB plus progesterone (P) priming. Although there were no group LQ differences after EB alone, S and FC animals showed an increase in LQ after EB plus P, whereas, FLC rats showed no change and this effect persisted for 180 day. Multiple regression analysis of FC and FLC coordinates indicated that the more posterior and lateral extending cuts were associated with lower LQ scores. Collectively, these data suggest a role for similar anterolateral MBH neural connections in (1) basal and cyclic gonadotrophin release and (2) EB plus P effects on lordosis behavior.