Comparative study of the functions of the caudal neurosecretory system in dogfish and zebrafish

The hypothalamus-pituitary complex is the most well-known neuroendocrine system in vertebrates. In fish, a second neuroendocrine system has been identified, called the caudal neurosecretory system, because of its position at the caudal end of the spinal cord. Like the hypothalamic-pituitary complex, the caudal neurosecretory system consists of two components: a small population of secretory neurons called Dahlgren cells, and a highly vascularized ventral expansion of nerve tissue called the urophysis (literally meaning "caudal pituitary"), towards which the Dahlgren cells project their axons and release hormones, called urotensins. Although these hormones are known to exert various actions, notably in the control of water balance and stress, the functions of the caudal neurosecretory system are still poorly understood. Initially characterized in teleost fishes, the caudal neurosecretory system is also present in all actinopterygians as well as chondrichthyans, suggesting that it is an ancestral attribute of gnathostomes. Furthermore, the absence of this system in tetrapods suggests that it was lost at the latest at the base of this lineage. My PhD project aims to better understand the functions of the caudal neurosecretory system by using the dogfish Scyliorhinus canicula and the zebrafish Danio rerio as models.