C-FOS EXPRESSION IN SPECIFIC RAT-BRAIN NUCLEI AFTER INTESTINAL ANAPHYLAXIS - INVOLVEMENT OF 5-HT3 RECEPTORS AND VAGAL AFFERENT-FIBERS

The c-fos immediate-early gene is acutely induced in brain after vario us stimuli from the digestive tract. 5-HT3 receptors and vagal afferen ts have been found involved in intestinal motor disturbances induced b y intestinal anaphylaxis. Our aim was to determine whether intestinal anaphylaxis activates brain structures, using c-fos expression, and to evaluate the modulation of c-fos induction by 5-HT3 receptors and vag al afferents. The effects of antigen challenge on intestinal motility were evaluated in ovalbumin-sensitized Hooded Lister rats chronically fitted with NiCr electrodes in the jejunal wall. Intestinal motility w as assessed in conscious rats pretreated or not by perivagal capsaicin or a 5-HT3 antagonist (ondansetron). In sensitized rats, ovalbumin di srupted for 62.4 +/- 9.5 min the jejunal migrating motor complexes (MM C) and an important c-fos expression was detected in the nucleus tract us solitarius (NTS), lateral parabrachial nucleus (LPB) and paraventri cular nucleus of the hypothalamus (PVN). Intraperitoneal administratio n of ondansetron or perivagal capsaicin treatment significantly reduce d the duration of MMC disruption and attenuated markedly c-fos stainin g in the 3 brain sites. In contrast, intracerebroventricular administr ation of ondansetron significantly reduced jejunal motor alterations b ut did not diminish the c-fos expression, suggesting a role of central 5-HT3 receptors in the efferent control of the intestinal disturbance s. Blockade of both c-fos expression and MMC disruption by systemic on dansetron and by perivagal capsaicin indicates that some brainstem nuc lei are involved in digestive disturbances after intestinal anaphylaxi s, and reflects an involvement of peripheral 5-HT3 receptors on vagal afferents. The reduction of c-fos staining in NTS as well as in LPB an d PVN after perivagal capsaicin suggests that the NTS is the primary r elay in the activation of the central nervous system during intestinal allergic challenge.