NEUROENDOCRINE AND AUTONOMOUS MECHANISMS UNDERLYING THERMOREGULATION IN COLD ENVIRONMENT

This review focuses on the central regulation of thermoregulatory resp onses with special attention to the participation of thyrotropin-relea sing hormone (TRH) in both autonomous and endocrine responses to a col d environment. Besides a direct projection of TRH neurons from paraven tricular nuclei (PVN) to the median eminence, and the subsequent activ ation of the thyroid axis, there are direct projections from the PVN t o the autonomic preganglionic neurons controlling autonomous responses . These projections convey information to peripheral targets involved in thermogenesis through the dorsal vagal complex and the spinal cord, for parasympathetic and sympathetic neurotransmissions respectively. Furthermore, cold exposure increases TRH mRNA levels in the PVN but al so in dorsal motor and caudal raphe nuclei, thus providing strong evid ence for a functional link between autonomous and neuroendocrine syste ms involved in thermoregulation. The review also focuses on neuroendoc rine regulation of cold-induced TRH/TSH release associated with modifi cations in somatostatin release, with special reference to the partici pation of several central neurotransmitters (catecholamines, serotonin or GABA) or the influence of sex steroids.