Immediate-early gene expression in the inferior mesenteric ganglion and colonic myenteric plexus of the guinea pig

Balloon passage induced c-fos and JunB in only a small subset of IMG neuron s and no myenteric neurons. However, balloon passage induced c-fos and JunB in IMG neurons (notably those containing somatostatin) and the myenteric p lexus of acetic acid-treated animals. After capsaicin treatment, c-fos and JunB induction by balloon passage was inhibited in the IMG, but there was e nhanced c-fos expression in the myenteric plexus. c-fos and JunB induction by balloon stimulation was also mimicked by acute activation of capsaicin-s ensitive nerves, These data suggest that colitis enhances reflex activity o f the IMG by a mechanism that involves activation of both primary afferent fibers and the myenteric plexus. Activation of neurons in the inferior mese nteric ganglion (IMG) was assessed using c-fos, JunB, and c-Jun expression in the guinea pig IMG and colonic myenteric plexus during mechanosensory st imulation and acute colitis in normal and capsaicin-treated animals. Intrac olonic saline or 2% acetic acid was administered, and mechanosensory stimul ation was performed by passage of a small (0.5 cm) balloon either 4 or 24 h r later. Lower doses of capsaicin or vehicle were used to activate primary afferent fibers during balloon passage, c-Jun did not respond to any of the stimuli in the study. c-fos and JunB were absent from the IMG and myenteri c plexus of untreated and saline-treated animals. Acetic acid induced acute colitis by 4 hr, which persisted for 24 hr, but c-fos was found only in en teric glia in the myenteric plexus and was absent from the IMG.