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MODULATION OF ELECTRICALLY EVOKED RESPONSES IN RAT DUODENUM BY ACTIVATION OF NICOTINIC CHOLINOCEPTORS
Author(s) -
Sotirov Emil S,
Itzev Dimitar E,
Papasova Maria P
Publication year - 1998
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.1998.tb02359.x
Subject(s) - chemistry , neuroscience , acetylcholine , duodenum , nicotinic agonist , modulation (music) , cholinergic , parasympatholytic , endocrinology , medicine , biology , muscarinic acetylcholine receptor , receptor , physics , acoustics
SUMMARY 1. The effect of activation of nicotinic cholinoceptors in rat duodenal segments following electrical field stimulation (EFS) was investigated. 2. Electrical field stimulation elicited a two‐component response: transient relaxation followed by contraction. The EFS‐evoked response was tetrodotoxin (TTX; 1 μmol/L) sensitive. The relaxation component was NG‐nitro‐L‐arginine (L‐NNA; 100 μmol/L) sensitive, while the contractile response was atropine (1 μmol/L) sensitive. 3. 1,1‐Dimethyl‐4‐phenyl‐piperazinium iodide (DMPP; 20 μmol/L) induced relaxation of spontaneously active preparations that was L‐NNA sensitive. L‐Arginine (1mmol/L) reversed the effects of L‐NNA on DMPP‐induced relaxation. 4. When EFS was applied, DMPP increased the amplitude of the relaxation component of the response and reduced the contractile component. 5. In the presence of L‐NNA, the effect of DMPP on the relaxation component of the response to EFS was reduced, but the contractile response was not affected. L‐Arginine partly reduced this effect of l‐NNA. 6. Neither propranolol (1 μmol/L) nor yohimbine (1 μmol/L) had any effect on the actions of DMPP on EFS‐evoked responses, but prazosin (1 μmol/L) strongly reduced the effect of DMPP on the contractile component of the response to EFS and slightly reduced the effect of DMPP on the relaxation response. 7. Histochemical studies demonstrated that, in the myenteric plexus of the rat duodenum, there are many reduced nicotinamide adenine dinucleotide phosphate‐diaphorase (N ADPH‐d)‐positive neurons and that their number decreased after treatment with L‐NNA. In the presence of L‐arginine and L‐NNA, the number of NADPH‐d‐positive neurons was similar to that found in control samples. 8. The data suggest that activation of nicotinic cholinoceptors modulates EFS‐evoked responses in the rat duodenum as a result of the potentiation of nitrergic and adrenergic neurotransmission.