Sodium intake and changes in c‐fos expression in forebrain and hindbrain areas induced by baclofen into the lateral parabrachial nucleus

In the present study, we investigated the effects of baclofen (GABA B receptor agonist) injected bilaterally into the lateral parabrachial nucleus (LPBN) on 1.8% NaCl, water and food intake and on c‐fos expression in forebrain and hindbrain areas in rats. Satiated and normovolemic male Holtzman rats (280–320 g) received bilateral injections of baclofen (0.5 nmol/0.2 μl) into LPBN and had immediate access to water, 1.8% NaCl and food for 4 h to test the ingestion or were maintained in the absence of water, NaCl or food and killed 2 h later for the study of c‐fos protein expression. Baclofen into the LPBN induced 1.8% NaCl (18±8 ml vs. saline: 1±1 ml/4 h), but not water or food intake. Baclofen injected into LPBN increased c‐fos expression in the comissural nucleus of tractus solitarius (cNTS) (1915±376 vs. saline: 198±79 positive cells/mm 2 ) and reduced c‐fos expression in the ventral median preoptic nucleus (vMnPO) (225±61 vs. saline: 1225±361 positive cells/mm 2 ), with no changes in the area postrema, organum vasculosum of the lamina terminalis, subfornical organ, amigdaloid complex, dorsal median preoptic nucleus, paraventricular nucleus of the hypothalamus and supraoptic nucleus. The results show a natriorexigenic effect of baclofen injected into the LPBN, together with the activation of cNTS and deactivation of vMnPO neurons. Financial support: FAPESP, CAPES, CNPq, PRONEX.