Trophic Effects of Androgen: Development and Hormonal Regulation of Neuron Number in a Sexually Dimorphic Vocal Motor Nucleus

ABSTRACT: In Xenopus laevis, the laryngeal mo-tor nucleus (n. of cranial nerves IX-X) is part of a sexually differentiated, androgen sensitive neuromuscu-lar system devoted to vocalization. Adult males have more n. IX-X neurons than females; however, during development of n. IX-X, the rate of neurogenesis does not appear to differ between the sexes. In this study, we explored the role of naturally occurring cell death in the development of this nucleus and asked whether cell death might be involved in establishing the sex differ-ence in neuron number. Counts of n. IX-X neurons reveal that at tadpole stage 56, males and females have similar numbers of n. IX-X neurons, but by stage 64 male neuron numbers are greater. This sex difference arises owing to a greater net loss of neurons in females