Neuroendocrine Regulation of Behavioral Differences

Michigan State University, East Lansing MI

Investigators

Abstract

Gender and seasonal differences in reproductive behaviors are often paralleled by differences in the morphology of structures controlling them. Although such dimorphisms are fundamental characteristics of numerous vertebrates, the mechanisms involved appear to vary. Steroid hormones often mediate both anatomy and function, but organisms differ in which hormone is important and critical age and in which sex it acts. Some of these differences may reflect constraints imposed by the animals or their environments, but others may reflect the type of system (e.g., courtship or copulatory). The proposed experiments investigate two neuromuscular systems required to coordinate a suite of masculine reproductive behaviors in green anole lizards. Males extend a throat fan (dewlap) to court females, and the motoneurons and muscles controlling this display have several male-biased characteristics. The hypothesis that steroid hormones regulate differentiation of these structures will be tested, and hormones specifically involved will be identified, thus determining when and where they act. Males also use one of two hemipenes during copulation, which are controlled by two pairs of muscles. Adult females do not have these structures. Relevant spinal motoneurons are larger and more numerous in males. Unlike the dewlap system, which appears stable in adulthood, preliminary results suggest that at least the copulatory muscles are plastic in adult males. Experiments will investigate whether the copulatory muscles and motoneurons change morphologically between the breeding and non-breeding seasons, and whether these changes can be induced by testosterone. Then, as for the dewlap system, the role of gonadal hormones in sexual differentiation of the copulatory neuromuscular structures will be assessed. The courtship system differentiates in juveniles, whereas the copulatory system is sexually dimorphic at hatching. This proposal will address the important question, "Why do some systems loose their responsiveness to gonadal hormones while others remain plastic during development and into adulthood ?".The broader impacts of the proposed work involve advancing scientific discovery by increasing the understanding of mechanisms involved in sculpting the structure of the nervous system and muscles, both in developmental organization and adult plasticity. At the same time teaching, training, and learning will be promoted, the participation of underrepresented groups in lab work will be encouraged, scientific result will be disseminated in a timely fashion, and the infrastructure for neuroendocrine research at this university will be enhanced