Sexual dimorphisms in the brainstem of the green anole lizard.

Male green anoles (Anolis carolinensis) court females by extending a bright red throat fan, called a dewlap. The dewlap is larger in males than in females who do not display the structure in the context of courtship. The ceratohyoid muscle and second ceratobranchial cartilage which control dewlap extension are significantly larger in male than in female anoles. Neurons innervating the ceratohyoid muscle were retrogradely labeled by injecting the muscle with fast blue and were found to be located in the vagal portion of nucleus ambiguus (Amb X), as well as in the region containing the glossopharyngeal portion of nucleus ambiguus (Amb IX) and the ventral portion of the motor nucleus of the facial nerve (nVIImv). Cells in both areas were larger in males than in females. These parallels between structure and function provide the opportunity to study mechanisms of sexual differentiation of brain and behavior.