Modular and functionally-different descending recto-anal motor pathways in a rat model |
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Authors: | Galya Stavreva Neli Nedialkova Negrin Negrev Dimitar Maslarov Radomir Radomirov |
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Institution: | 1.Department of Experimental and Clinical Pharmacology,Medical University,Pleven,Bulgaria;2.Institute of Neurobiology,Bulgarian Academy of Sciences,Sofia,Bulgaria;3.Department of Physiology and Pathophysiology,Medical University,Varna,Bulgaria;4.Neurology Clinic,First Hospital for Active Treatments,Sofia,Bulgaria |
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Abstract: | We evaluated the motor responses in recto-anal preparations obtained from rats, in terms of the excitation displayed by modules
of nerve networks and descending distally directed pathways, when subjected to the mechanographic on-line technique, a partitioned
organ bath, electrical stimulation (EFS, 0.8 ms, 5 Hz) and distension. EFS elicited modular contractions, which increased
in amplitude distally, in circular muscle rings isolated from the proximal, middle or distal rectum. The modular responses
of the internal anal sphincter or anal canal were relaxation or contraction, respectively. The application of EFS to the distal
rectum induced a descending contractile response in the anal canal (5.24±0.34 mN), while distension by balloon evoked a descending
response consisting of contraction (1.72±0.20 mN) followed by relaxation (3.42±0.24 mN). The responses were sensitive to tetrodotoxin.
Atropine considerably depressed the contractions in all preparations. Whether or not atropine was present, L-NNA increased
the excitatory responses, while L-arginine decreased the contractions and extended the relaxation of internal anal sphincter
and anal canal. The results suggest that excitatory neurotransmission(s) expressed in the distal rectum dominate modular nerve
networks. Functionally-different descending pathways are involved in the motor activity of the anal canal. Stimulatory cholinergic
pathways are dependent on the electrically-induced excitation, and inhibitory nitrergic pathways are sensitive to distension
of rectal wall. |
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