title: Sex differences in the motor nucleus of cranial nerve IX-X in Xenopus laevis: a quantitative Golgi study.
abstract: In the clawed frog (Xenopus laevis), motor neurons in cranial nerve nucleus IX-X control contraction of laryngeal muscles responsible for sexually dimorphic vocal behaviors. We examined sex differences in dendritic arbors of n.IX-X cells using the Golgi-Cox method. Three morphological classes of somal types (ovoid, triangular, and elongate) are present in similar frequencies in n.IX-X of both males and females. The male n.IX-X neuron is a more complex and hypertrophied version of the female n.IX-X cell. The number of primary dendrites is the same for both sexes, but males have more total dendritic segments. The overall dendritic length of male n.IX-X neurons is two to three times that of the female. Males have longer dendritic segments between all branch points. Male and female frogs differ in levels of circulating androgens; neurons of n.IX-X are targets for androgenic steroids. To determine if androgen can affect dendritic morphology in adult females, we examined Golgi-impregnated cells in n.IX-X from ovariectomized females treated with testosterone for 1 month. The total number of dendritic segments was reduced by androgen treatment due to reduction in the number of higher order dendritic segments; the number of primary dendritic segments was unchanged. Androgen treatment may induce resorption of higher order dendritic branches. The overall dendritic length of androgen-treated female n.IX-X neurons was unchanged, and dendritic segments were longer. Thus, although androgen can alter dendrites of n.IX-X cells in adult females, this short-term treatment does not produce a masculine dendritic architecture.
authors.affiliation: Department of Biological Sciences, Columbia University, New York, New York 10027.
authors.forename: D B
authors.initials: DB
authors.lastname: Kelley
authors.forename: S
authors.initials: S
authors.lastname: Fenstemaker
authors.forename: P
authors.initials: P
authors.lastname: Hannigan
authors.forename: S
authors.initials: S
authors.lastname: Shih
mesh_terms: D000818:Animals; D005260:Female; D005930:Glossopharyngeal Nerve / Q000166:cytology* / Q000502:physiology; D008297:Male; D009046:Motor Neurons / Q000166:cytology* / Q000502:physiology; D012737:Sex Factors; D013739:Testosterone / Q000494:pharmacology; D014630:Vagus Nerve / Q000166:cytology* / Q000502:physiology; D014828:Vocalization, Animal; D014982:Xenopus laevis / Q000033:anatomy & histology* / Q000502:physiology
chemical_list: D013739:Testosterone