Ž . Brain Research 829 1999 197–200 Short communication Ž . Anteroventral third ventricle AV3V lesions alter c-fos expression induced by salt loading Maria Jose A. Rocha a, ) , Terry G. Beltz b , Rita Cassia M. Dornelles a , Alan Kim Johnson b , ´ ´ Celso Rodrigues Franci a a Departamento de Fisiologia, Faculdade de Medicina de Ribeirao Preto, UniÕersidade de Sao Paulo, AÕ. Bandeirantes, 3900, CEP 14049-900, Ribeirao ˜ ˜ ˜ Preto, SP, Brazil b Departments of Psychology and Pharmacology and the CardioÕascular Center, UniÕersity of Iowa, Iowa City, IA 52242, USA Accepted 9 March 1999 Abstract Ž . Lesion of the anteroventral third-ventricle region AV3VX reduced saline consumption. Salt loading in AV3VX rats resulted in reduced but not completely abolished c-fos expression in the supraoptic and paraventricular nuclei. Intrinsic osmosensitivity of the magnocellular neurons, or input from other brain areas, such as the subfornical and median preoptic nuclei, may account for this residual c-fos expression. These regions showed c-fos expression following salt loading. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Fos-protein; Osmotic stimulus; Vasopressin; Oxytocin; Hypothalamus Neurons of the anteroventral region of the third ventri- Ž . cle AV3V project to the vasopressinergic and oxytociner- Ž . gic neurons of the supraoptic SO and paraventricular Ž . w x PVH nuclei of the hypothalamus 2,5,14 . Lesion of Ž . AV3V AV3VX causes chronic hypernatremia with an impairment to excrete sodium loads, attenuated experimen- tal hypertension, and impaired responses to experimental w x challenges that elicit drinking and hormone secretion 7,8 . In response to chronic salt consumption, AV3VX increases Ž . Ž . vasopressin VP and oxytocin OT mRNA in the SO or w x PVH, without affecting hormone secretion 13 . Thus, the neuroendocrine response requires input from the AV3V, but VP or OT expression apparently is stimulated by other pathways. Vasopressinergic and oxytocinergic neurons ex- hibit increased Fos-protein expression following an os- w x motic stimuli 3,4 . However, it is not yet clear whether there is a direct relationship between increased c-fos ex- pression, and VP and OT expression. The aim of this study was to investigate the consequences of AV3VX on c-fos expression in magnocellular neurons of the SO and PVH following osmotic stimulus. ) Corresponding author. E-mail: mjrocha@rfi.fmrp.usp.br Ž . Male Sprague–Dawley rats 250–350 g were anes- Ž . thetized with Equithesin 0.33 mlr100 g b.wt. and sub- Ž . jected to anodal electrolytic lesion 2.5 mA for 25 s in the Ž . AV3V region, or to sham-lesion, control with a 24-gauge nichrome wire. The stereotaxic coordinates of the midline lesion were: 0.0–0.2 mm posterior to bregma and 7.5 mm ventral to the midsagittal sinus. The animals were housed under controlled conditions with food and water ad libi- tum. Animals that drank less than 10 ml over a 24 h period following lesion were functionally regarded as lesioned. They received a 10% sucrose solution to drink in order to provide adequate hydration, and were gradually weaned from the sucrose to water by successively reducing the concentration of sucrose. At the time of the experiment, 3 weeks post surgery, the AV3VX and control groups con- sumed comparable amounts of water and food. Ž . Ž . Control n s 7 and AV3VX n s 4 groups received Ž tap water or 2% NaCl solution n s 6 and n s 5, respec- . tively to drink. An additional sham-lesion group was included in which salt intake was matched to that of Ž . AV3VX restricted control, n s 7 . After 3 days, the ani- mals were anesthetized and perfused transcardially with 50 Ž . ml of phosphate-buffered saline PBS, pH 7.4 and 500 ml of 4% paraformaldehyde in 0.1 M phosphate buffer. The 0006-8993r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0006-8993 99 01366-9