Suppression of sexual receptivity in the female hamster: neuroanatomical projections from preoptic and anterior hypothalamic electrode sites.

Electrical stimulation (ES) through fine-wire electrodes chronically implanted in the preoptic area and anterior hypothalamus suppressed the lordosis response in freely moving hormone-primed female hamsters. ES at these sites never induced or facilitated lordosis. When behavioral testing was completed small lesions were made at the tips of the electrodes, and the Fink-Heimer method was used to trace degenerating axons away from the sites of ES. This was done in an effort to determine the neural pathways important for the modulation of this behavior. The hypothalamic distribution of the stria terminalis was also charted for the hamster and was found to be similar to that in the rat, including projections to both the shell and core of the ventromedial nucleus (VMN). No single pattern of degeneration was common to all females showing ES-produced lordosis suppression. These data demonstrate that stimulation of several different pathways can produce behavioral states that are incompatible with the lordosis response. We suggest that ES in the medial preoptic-medial anterior hypothalamic continuum suppresses sexual receptivity by influencing neurons in the VMN region, while ES through more laterally placed electrodes suppresses receptivity by producing an incompatible state of behavioral activation, without directly influencing VMN region neural activity.