Evidence That Androgen Acts Through NMDA Receptors to Affect Motoneurons in the Rat Spinal Nucleus of the Bulbocavernosus

In adult male rats, spinal nucleus of the bulbocavernosus (SNB) motoneurons shrink after castration and are restored in size after androgen treatment. Sixty-day-old Sprague Dawley males were castrated and implanted with SILASTIC capsules contain-ing testosterone (T) or nothing, and osmotic minipumps con-tinuously infusing MK-801, a noncompetitive NMDA receptor antagonist, or saline. Twenty-five days later, bulbocavernosus muscles were injected with the retrograde tracer cholera toxin-horseradish peroxidase conjugate (CT-HRP) to label SNB cells. As seen previously, among saline-treated rats, SNB somata of T-treated castrates were significantly larger than those of cas-trates receiving blank capsules ( p 0.0001). MK-801 treat-ment blocked this effect of T on the SNB. MK-801 had no effect on non-androgen-responsive spinal motoneurons in the neigh-boring retrodorsolateral nucleus (RDLN), nor did the drug affec