Introduction. The role of neurotransmitter systems in the motor activity of longitudinal or circular muscles in autonomic regulation of the motility of the colon by the nervous system is unclear.
The aim of the study was to investigate the neu-rotransmitter implications in descending motility of longitudinal and circular muscles in rat colon.
Methods. Electrically-induced (2, 5 or 10 Hz, 0.8 ms, 40 V, 20 s) local or descending motor responses of lon-gitudinal and circular muscles in isolated preparations and drugs were used to define the neurotransmitters’ role in colonic motility.
Results. The spontaneous activity of the distal part of preparations manifested as high-amplitude irregu-lar contractions more expressed in the longitudinal muscles. The electrically -induced local responses dif-fered considerably in the two muscles: in longitudinal muscle there were frequency-dependent contractions, while initial relaxation followed by contraction was observed in circular muscle. The descending motor response resembled the pattern of the local responses, but the amplitudes were significantly less expressed, as compared to the respective local responses. In atropine-pretreated (0.3 μ M) preparations, the contrac-tions of longitudinal and circular muscle significantly decreased, and initial relaxation preceded the contrac-tions of the longitudinal muscle. In the presence of atropine, spantide (0.1 μM) reduced more noticeably the contractile components of responses in both mus-cles. L-NNA (0.5 mM) restored to a great extent the de-scending contractions of the longitudinal and circular muscles, while L-Arginine (0.5 mM) strongly depressed the contractions and more significantly increased the relaxation in circular muscle.
Conclusions. The present results suggest the implica-tion of both cholinergic and tachykininergic systems as excitatory neurotransmissions in the colonic descend-ing reflex pathways and the involvement of nitrergic neurotransmitter systems in the descending inhibito-ry neuromuscular signalization predominantly serving the circular muscle.
Keywords: atropine, L-arginine, NG-nitro-L-arginine, spantide, descending reflex pathways, rat colon.
CM – circular muscle
EFS –electrical field stimulation
L-NNA – NG-nitro-L-arginine
LM –longitudinal muscle
NO – nitric oxideFull text sources