3H-estradiol, 3H-testosterone and 3H-dihydrotestosterone localization in the brain of the lizard Anolis carolinensis: an autoradiographic study.

The presence and the neuroanatomical topography of sex hormone concentrating cells in the brain of the American chameleon, Anolis carolinensis have been demonstrated by these experiments. After 3H-estradiol administration large numbers of hormone concentrating cells were found in the amygdala, septum, medial preoptic area, anterior hypothalamic area, the ventromedial and periventricular nuclei of the hypothalamus, and anterior pituitary. In addition, labelled cells were found in the torus semicircularis, in and around the nucleus isthmus pars parvocellularis. A small number of labelled cells could also be found in the rostral pallium, motor nucleus of the fifth cranial nerve, the raphé nuclei, and the spinal cord. After 3H-testosterone or 3H-dihydrotestosterone administration the neuroanatomical pattern was very similar to that found after 3H-estradiol; however, fewer labelled cells were seen after the androgens were given. Two exceptions to the similarity of pattern were in a caudal part of the pallium and in the mesencephalic tegmental area. Hormone-concentrating cells were found after 3H-testosterone or 3H-dihydrotestosterone administration, while labelled cells in these two areas after 3H-estradiol administration were extremely rare. The pattern of hormone-concentrating cells was the same in male and female brains, for each of the hormones. The preoptic area, hypothalamus, and anterior pituitary have been demonstrated in reptiles to be involved in neuroendocrine regulation and in the control of sex behaviors. The presence and neuroanatomical pattern of sex steroid binding cells in the brains of a wide variety of vertebrates have been documented. Large numbers of hormone-concentrating cells were found in all of these species in the medial preoptic area, tuberal hypothalamus, specific limbic structures, the mesencephalon deep to the tectum, and the anterior pituitary. Most hormone-concentrating cells in the brain of A. carolinensis were found in these same brain regions, thus indicating a vertebrate-wide stable core of hormone-concentrating cells in neuroanatomically defined regions.