Plasticity of neuroendocrine mechanisms regulating seasonal reproduction in sheep

Abstract : The sheep is not only a valuable animal model in which to investigate the mechanisms underlying seasonality, it is a commercially important species where reproduction of many breeds is profoundly seasonal. This chapter will describe how studies in sheep have revealed plasticity in the hypothalamus that likely underlies seasonal changes in neuroendocrine function. This includes changes in the kisspeptin neuronal system that provides a key drive to the gonadotrophin-releasing hormone (GnRH) secretory system, seasonal fluctuations in neurogenesis, and cell fate in the hypothalamus, morphological reorganizations as revealed by changes in polysialylated neural cell adhesion molecule immunoreactivity, and changes in permeability of the blood-brain barrier