Electrical field stimulation (0.8 ms, 40 V, 2–5–10 Hz, 20 s) applied at the oral or the distal part of isolated segments of rat colon mounted in two-compartments organ bath was used to excite the nerve structures mediating the local or ascending responses of the circular muscle. To evaluate the neurotransmissions involved in the ascending reflex pathways the ascending motor responses were studied by cholinergic, tachykininergic and nitrergic-related drugs. The electrically-induced ascending responses of the colonic circular muscle were frequency-dependent contractions. Atropine (0.3 µM) added to the oral compartment of the bath converted the ascending contractions of the circular muscle induced by stimulation applied at a frequency of 5 Hz to motor responses consisting of an initial relaxation followed by a contraction (atropine-mediated contraction of 2.0±0.24 mN vs. control of 4.1±0.6 mN , p < 0.05). Spantide (0.3 µM), added in the presence of atropine reduced the contraction more without changing the relaxation indicating that besides cholinergic, the tachykininergic neurotransmission is presented in ascending stimulatory motor responses. L-NNA (0.5 mM ) reduced the relaxation and significantly restored the atropinedecreased contraction while L-Arginine (0.5 mM ) provoked a deep relaxation in atropine-pretreated colonic segments, thus suggesting modulation role of inhibitory nitrergic neuro
Key words: rat colon, neurotransmission, ascending motor responses
Topic: MEDICINE