Immunoreactive gonadotropin-releasing hormone (GnRHir) is associated with vestibular structures in the green anole (Anolis carolinensis).

Abstract

The distribution of immunoreactive gonadotropin-releasing hormone (GnRHir) in relation to endocrine and behavioral pathways is not well established for lizards. To more completely understand the GnRHir distribution and its possible function in a lizard, we investigated the brain of Anolis carolinensis, a species whose visual courtship displays, mating postures and gonadal cycles are well known. Using antisera that recognize multiple GnRH forms, we observed no GnRHir cells or fibers in the forebrain. In the midbrain, however, GnRHir cells occurred along the medial border of the medial longitudinal fasciculus. These cells appeared to project GnRHir fibers to nuclei of cranial nerve III and IV. In the hindbrain, positive fibers were observed in the area of the vestibular nuclei and dorsal funiculus. These hindbrain fibers were followed to their terminals in the cerebellum. The GnRHir midbrain distribution suggests an association of GnRH with eye movements, whereas the hindbrain distribution suggests a GnRH-vestibular association. The lack of GnRHir in the forebrain of Anolis could reflect the minimal role of the vomeronasal system in mediating reproduction in this species. Thus, our study cannot verify hypothalamic GnRH control of the pituitary in A. carolinensis, but it does indicate GnRH control of oculomotor and vestibular nuclei, which might play a role in Anolis reproductive behaviors.