title: Locality-dependent descending reflex motor activity in the anal canal--cholinergic and nitrergic contributions in the rat model.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Institute of Neurobiology, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria. radomir@bio.bas.bg
authors.forename: Radomir
authors.initials: R
authors.lastname: Radomirov
authors.forename: Christina
authors.initials: C
authors.lastname: Ivancheva
authors.forename: Dimitar
authors.initials: D
authors.lastname: Itzev
authors.forename: Polina
authors.initials: P
authors.lastname: Petkova-Kirova
mesh_terms: D001003:Anal Canal / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D018678:Cholinergic Agents / Q000494:pharmacology*; D002799:Cholinergic Fibers / Q000187:drug effects; D005769:Gastrointestinal Motility / Q000187:drug effects* / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D026602:Nitrergic Neurons / Q000187:drug effects; D019335:Nitroarginine / Q000494:pharmacology; D009924:Organ Culture Techniques; D010276:Parasympatholytics / Q000494:pharmacology; D051381:Rats; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D018678:Cholinergic Agents; D010276:Parasympatholytics; D026941:Sodium Channel Blockers; D019335:Nitroarginine; D013779:Tetrodotoxin; D001285:Atropine; D001120:Arginine
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