Synthesis of nitric oxide in the paraventricular nucleus of the hypothalamus and in the dorsal motor nucleus of the vagus mediates the acid inhibitory effects of centrally administered bombesin

Abstract

general and inflammatory bowel disease (IBD) in particular has not been well characterised. We have recently reported a significant increase in the level of enteric PACAP and the presence of immune cells containing the peptide in the serosa layer of ileum of Crohn's patients (Belai et al., Gut, 1997 40:767774). The aim of the present study was to determine the involvement of PACAP and its receptor (PACAP-R) in the inflammatory responses known to occur in the distal colon of TNB-colitis rat model. Methods: Colitis was induced in fasted female Lewis rats by intracolonic administration of 2,4,6,trinitrobenzensulfonic acid (TNB=80 mg/Kg, in 50% ethanol) and the animals were sacrificed 7 days after induction of colitis. Control rats received identical volume of vehicle (50% ethanol). Segments of control and inflamed distal colon were processed for immunohistochemical localisation using specific antibodies against PACAP, PACAP-R and CD4 +. The percentage of PACAP-R positive immune cells which are immunoreactive to both CD4 ÷ PACAP was determined using co-localisation studies. Results: TNB induced severe inflammation in the distal colon and there was extensive infiltration of mucosal and muscular coat of the lesioned colon by inflammatory cells, which was not seen in the vehicle-treated controls. A large proportions (>80%) of the inflammatory cells were found to express PACAP-Rs. The density of the inflammatory cells was scored as very high at the epithelial layer (region 1), high at the submucosa layer (region 2), and moderate at the outer muscular coat layers (region 3) of the lesioned colon. The immune cells were quantified and taking the number of inflammatory cells that express PACAP-R as 100% (n=5), the percentage of PACAP-R positive cells that are PACAP27or CD4 + -immunoreactive was determined.