Locality-dependent descending reflex motor activity in the anal canal--cholinergic and nitrergic contributions in the rat model.

AIM: Since the distal part of the intestine is targeted by a wide range of pathogens, the motility of the recto-anal region has been the object of many experimental and clinical observations. In this study, we investigated descending motor responses in the anal canal as a measure of the activation of autonomic reflex pathways underlying evacuatory recto-anal activity. METHODS: The partitioned organ bath method was used to register motor responses of the anal canal as induced by balloon distension of the rectum in isolated rat recto-anal preparations. RESULTS: Distension-induced descending responses of the anal canal comprised contractions (with distension at a distance of 15 mm), initial contractions and secondary relaxations (at 10 mm) and short contractions followed by deep relaxations (at 3-5 mm). Decreasing the distance between the distension stimulus and the anal canal resulted in a decreased contraction response and increased relaxation. Tetrodotoxin (0.1 micromol/L) inhibited these responses. Atropine (0.3 micromol/L) decreased contraction and did not change the relaxation response. N(G)-nitro-L-arginine (0.5 mmol/L) enhanced contraction in both the absence and presence of atropine. L-arginine (0.5 mmol/L) inhibited contraction and extended relaxation in atropine-pretreated preparations. The actions of N(G)-nitro-L-arginine and L-arginine were more pronounced in the aboral direction. ChAT-positive nerve fibers were observed in myenteric ganglia of the rectum and the anal canal. The density of NADPH-diaphorase-positive neurons was higher in the anal canal region. CONCLUSION: Our results suggest that locality-dependent activation of the descending reflex neuromuscular communications underlie evacuatory activity in the recto-anal region. This activation response involves long excitatory cholinergic and non-cholinergic pathways along the rectum and short inhibitory nitrergic pathways located predominantly in the anal canal region.

Ascending and descending reflex motor activity of recto-anal region-cholinergic and nitrergic implications in a rat model.

The implications of cholinergic and nitrergic transmissions in ascending and descending reflex motor pathways of recto-anal region in rat model were evaluated using: (i) electrical stimulation; (ii) triple organ bath; and (iii) morphological techniques. Electrical stimulation to anal canal induced simultaneous ascending contractile responses of longitudinal and circular muscles of proximal rectum, local contraction of anal canal or contraction followed by relaxation of internal anal sphincter when external sphincter was dissected off. The stimulation of proximal rectum elicited local contractions of both rectal layers and descending contractions of internal sphincter or anal canal. Tetrodotoxin (0.1 microM) prevented the electrically elicited events. The ascending excitatory responses and the local and ascending contractions of longitudinal muscle were more pronounced than those of circular muscle suggesting dominant role of ascending reflex pathways and of longitudinal muscle in rectal motor activity. Choline acetyltransferase (ChAT)-containing fibres and nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase-positive neurons were observed in myenteric ganglia of rectum and anal canal. NG-nitro-l-arginine (0.5mM) increased the contractile ascending and descending responses. During atropine (0.3 microM) treatment the ascending and descending contractions were suppressed but not abolished and a relaxation revealed in ascending response of circular muscle and in descending responses of internal anal sphincter and anal canal. The relaxation was decreased by NG-nitro-l-arginine and increased by l-arginine (0.5mM). The results suggest that cholinergic excitatory ascending and descending pathways and nitric oxide-dependent inhibitory ascending neurotransmission(s) to rectal circular muscle and inhibitory descending to internal anal sphincter and anal canal are involved in reflex circuitry controlling motor activity of recto-anal region.