Sexual steroids in Salamandra salamandra (L.) during ontogeny

Targeted expression of androgen receptors in tooth-forming tissues of a neotropical salamander (Bolitoglossa schizodactyla) enables region-specific formation of dimorphic types of teeth in the male

Bicuspid teeth are a morphological characteristic in adult metamorphosed urodeles. However, during the mating season the males of many species of plethodontid salamanders (Urodela, Plethodontidae) from northern America bear large monocuspid teeth on their jaws. Since androgen levels are elevated during the mating season, it is likely that the formation of monocuspid teeth is controlled by androgens. However, many plethodontid salamanders from southern Central America live in habitats which lack significant seasonal changes and therefore are no seasonal breeders. These males constantly bear monocuspid teeth, however their presence is restricted to the premaxillary bone, which forms the most frontal element of the upper jaw. Teeth of all other dentigerous bones are bicuspid. This study is based on an immunohistochemical localisation of androgen receptors and reveals a differential expression of androgen receptors in the three separate dental laminae of the upper jaw of Bolitoglossa schizodactyla (Urodela, Plethodontidae) from western Panama. Our findings suggest that the restriction of androgen receptor expression to the premaxillary dental lamina of the male and its absence in all other tooth-forming tissues leads to the differences in tooth morphogenesis. In conclusion, a differential and cell-specific expression of androgen receptors in urodeles-similar to the situation in mammalian species-allows a selective response of differentiating tissues to the hormonal status of the animal.

Ovarian steroid levels in Salamandra salamandra infraimmaculata during the reproductive cycle

Gonadal steroid levels were determined in the ovary of Salamandra salamandra infraimmaculata during the reproductive cycle in populations from a xeric region in northern Israel. Varying proportions of previtellogenic and vitellogenic oocytes were present throughout the year, and mature oocytes were present in winter and spring. The numbers of mature oocytes were greater between December and April, after parturition. The levels of 17 beta-estradiol and testosterone rose during oocyte vitellogenesis and maturation. Levels of progesterone and 17 alpha-hydroxy progesterone appeared to be related to the level of vitellogenesis. Gravid females contained greater quantities of all four steroids than did nongravid females.

Steroid-neuropeptide interactions that control reproductive behaviors in an amphibian

Investigations into the neuroendocrine regulation of reproductive behaviors in an amphibian (Taricha granulosa) reveal the same basic repertoire of chemical messengers as regulators of male behaviors in other vertebrates. These studies have identified seasonal neural interactions between gonadal steroids and neuropeptides that facilitate male courtship behavior. In addition, this species has served to elucidate how stress-induced suppression of courtship is mediated by corticosterone action through a neuronal membrane receptor and subsequent, rapid neurophysiological effects. These findings indicate that a principal mechanism by which steroids and neuropeptides control male reproductive behavior is the modulation of neural processing of specific sensory stimuli.