Testosterone uptake in the brainstem of a sound-producing fish.

Three nuclear areas in the medulla were implicated in the control of sound production in the oyster toadfish Opsanus tau. The sonic motor nucleus was labeled by retrograde transport of horseradish peroxidase injected into swimbladder sonic muscles, and an adjacent ventrolateral and a more anterior periventricular nucleus of the medulla were revealed by autoradiography with 3H-labeled testosterone. These androgen uptake sites occur in brainstem areas corresponding to areas predicted to contain the neural centers controlling the duration and fundamental frequency of the toadfish mating call.