Inhibition of male sexual behavior by intracranial implants of the protein synthesis inhibitor anisomycin into the medial preoptic area of the rat.

Castrated male rats received testosterone (T) via silastic capsules and bilateral implants of either anisomycin (ANI) in a cocoa butter/beeswax mixture or cocoa butter/beeswax alone as a control. Cannulae were placed directly into the medial preoptic area (MPOA) to determine if protein synthesis in this brain region is required for the expression of male sexual behavior. In the first experiment, using a restoration paradigm, it was found that a 25% mixture of ANI prevented restoration of male sexual behavior, whereas 4% ANI was only partially effective. In a second experiment, the ability of 25% ANI to suppress male sexual behavior in a maintenance paradigm was tested and found to be completely ineffective. In a third experiment, a 50% ANI dose was used and this dose significantly suppressed male sexual behavior by the fourth week. Sexual behavior returned following ANI discontinuation. Males receiving 50% ANI were also tested for sexual motivation (measured in a place preference test), as well as for scent marking and vocalizations. ANI implanted into the MPOA did not affect sexual motivation, as males in both ANI and control groups spent more time with a sexually receptive female than with a nonreceptive female. ANI in the MPOA did not affect scent marking, but significantly decreased ultrasonic vocalizations. These results suggest that, in rats, protein synthesis in the MPOA is required for the expression of male sexual behavior and vocalizations, but not for sexual preference or scent marking.