Estrogen implants in the lateral habenular nucleus do not stimulate the onset of maternal behavior in female rats

The natural onset of maternal behavior in the rat is hormonally mediated. E strogen, progesterone, and prolactin administered to ovariectomized females in amounts and sequences that produce circulating levels similar to those found during pregnancy stimulate the onset of maternal behavior. In fact, m aternal behavior can be stimulated by estrogen alone, administered either p eripherally or by implant in the central nervous system. The lateral habenu la (Lhb), which is a necessary component in the neural circuit that support s maternal behavior, contains a subset of neurons with estrogen receptors. The present study investigated whether estradiol implants directly in the L hb are sufficient to stimulate maternal behavior. Female rats, hysterectomi zed and ovariectomized on day 16 of pregnancy, received estrogen implants i n the Lhb or, as a positive control, in the medial preoptic area (MPOA). An additional control group received cholesterol implants in the Lhb. All fem ales were tested for pup retrieval, nest building, crouching behavior, loco motor activity, and carrying behavior. Estradiol implants into the Lhb did not stimulate the onset of maternal behavior. Females with estrogen implant s in the Lhb scored significantly lower in pup retrieval and crouching beha vior compared to females with implants in the MPOA and were not significant ly different from females with cholesterol implants in the Lhb. There were also no significant differences in overall activity or carrying behavior am ong the groups. (C) 1999 Academic Press.