J Comp Physiol B (2008) 178:57–66 DOI 10.1007/s00360-007-0199-7 123 ORIGINAL PAPER Hypothalamic activity during altered salt and water balance in the snake Bothrops jararaca Leonardo Zambotti-Villela · Camila Eduardo Marinho · Rafaela Fadoni Alponti · Paulo Flavio Silveira Received: 25 April 2007 / Revised: 20 July 2007 / Accepted: 28 July 2007 / Published online: 17 August 2007  Springer-Verlag 2007 Abstract The eVects of water and salt overload on the activities of the supraoptic and paraventricular nuclei and the adjacent periventricular zone of the hypothalamus of the snake Bothrops jararaca were investigated by measure- ments of Fos-like immunoreactivity (Fos-ir). Both water and salt overload resulted in changes in body mass, plasma osmolality, and plasma concentrations of sodium, potas- sium, and chloride. Hyper-osmolality increased Fos immu- noreactivity in the rostral supraoptic nucleus (SON), the paraventricular nucleus (PVN), and adjacent periventricular areas. Both hyper- and hypo-osmolality increased Fos immunoreactivity in the intermediate SON, but not in other areas of the hypothalamus. Immunostaining was abundant in cerebrospinal Xuid (CSF)-contacting tanycyte-like cells in the ependymal layer of the third ventricle. These data highlight some features of regional distribution of Fos immunoreactivity that are consistent with vasotocin func- tioning as a hormone, and support the role of hypothalamic structures in the response to disruption of salt and water balance in this snake. Keywords Fos · Body Xuid and electrolyte homeostasis · Hypothalamus · Supraoptic nucleus · Paraventricular nucleus · CSF-contacting cells Abbreviations AC Anterior commissure C Control group CSF Cerebrospinal Xuid Fos-ir Fos-like immunoreactivity OC Optic chiasma OD Optical density OT Optic tract PD Population density PeV Periventricular areas along the rostrocaudal extent of PVN and SON adjacent to these nuclei PVN Paraventricular nucleus R1 Region located caudally at 3,200 m from the ros- tral end of the olfactory bulb R2 Region located caudally at 200 m from R1 R3 Region located caudally at 560 m from R1 R4 Region located caudally at 780 m from R1 RCN Suprachiasmatic nucleus SL Salt-overloaded group SON Supraoptic nucleus WL Water-overloaded group Introduction Hypothalamo-neurohypophysial system is a major compo- nent of the neuroendocrine regulation of hydrodynamic bal- ance in all vertebrates, which consists of neurones and glial cells located in the paraventricular (PVN) and supraoptic (SON) nuclei (Rodríguez 1984). In mammals, these neuro- nes synthesize the peptides arginine vasopressin and oxyto- cin and release them into the blood circulation (Ludwig et al. 1997) and the extracellular space of hypothalamic tissue, whereas glial cells regulate the extracellular environ- ment of these neurones (Walz and Hertz 1983). Communicated by I.D. Hume. L. Zambotti-Villela · C. E. Marinho · R. F. Alponti · P. F. Silveira (&) Laboratory of Pharmacology, Instituto Butantan, Av. Vital Brazil, 1500, São Paulo, 05503-900 SP, Brazil e-mail: pefesil@butantan.gov.br