Changes in the Gonadotropin-Releasing Hormone (GnRH) Neuronal System during the Annual Reproductive Cycle of the Horseshoe Bat, Rhinolophus ferrumequinum

Abstract

Abstract Unique reproductive phenomena, such as delayed fertilization in females and asynchrony between spermatogenesis and mating behavior in males, are known in hibernating bats. The present study was undertaken to examine sex differences and seasonal changes in the gonadotropin-releasing hormone (GnRH)-immunoreactive (ir) neuronal system of Japanese bats, Rhinolophus ferrumequinum. GnRH-ir neurons were preferentially distributed in the medial preoptic area (POA) and medial basal hypothalamus (MBH). The number and immunoreactivity of GnRH-ir neurons decreased in summer (lactation period in females and spermatogenic period in males), whereas both increased dramatically in winter (hibernation period). The number and immunoreactivity of GnRH-ir neurons varied more in the MBH than in the POA throughout the annual reproductive cycle of both sexes. The changes in GnRH neurons in the MBH closely paralleled those of GnRH-ir fibers in the median eminence (ME), which is the release site for GnRH. In contrast, the...