Testosterone stimulation of the medial preoptic area and medial amygdala in the control of male hamster sexual behavior: redundancy without amplification

Receptors for gonadal steroids are present in an interconnected network of limbic nuclei. The existence of this network structure has important implic ations for how steroids control reproductive physiology and behavior. In 19 86, Cottingham and Pfaff proposed that properties of a steroid-responsive n eural network could include redundancy, amplification, stability and select ive filtering. The present study tested the concept of steroid amplificatio n, using male hamster sexual behavior as a model. In the male hamster, the medial amygdaloid nucleus (Me) and medial preoptic area (MPOA) are essentia l for mating behavior, and both nuclei transduce steroid cues to facilitate copulation. To determine if steroid action at multiple interconnected nucl ei amplifies mating, the present study compared sexual behavior in castrate d male hamsters bearing unilateral intracranial implants of testosterone in Me or MPOA with that of males with dual testosterone implants in Me and MP OA. Implants that stimulated androgen receptor-containing neurons in Me or MPOA stimulated copulatory behavior above castrate levels. However, behavio r of males with dual implants was not significantly different from that of males with single implants. This suggests that steroid action at either MPO A or Me is sufficient to facilitate mating, but dual stimulation of these r eciprocally-connected nuclei does not amplify sexual behavior. (C) 1999 Els evier Science B.V. All rights reserved.