In vitro motor activity of the lamprey ( Lampetra japonica) intestine

Abstract

The intestine of the lamprey (primitive vertebrate), was divided into four segments (SI-SIV) of about 4cm from oral to anal. The frequency and amplitude of their spontaneous motor activities (intraluminal pressure) were studied in vitro. Frequency gradient from oral SI (1.44 cycle/min) to anal SIV (0.26 cycle/min) was found. In contrast, the amplitude gradient (0.14–0.36 mmHg) was quite the reverse and SIV was the largest and SI was the smallest. Raising the temperature from 5 to 10–15°C almost linearly increased both frequency and amplitude in Arrhenius's plot. Acetylcholine (1–10 mM) and 5-HT (1–10 μM) directly induced the contractions of the longitudinal and circular smooth muscles in the presence of 1 μg/ml tetrodotoxin (TTX). Atropine (5–20 μM) shifted the dose-response curves of acetylcholine to the right but hardly affected the 5-HT responses. Spiperone and ketanserine (10–40 μM) shifted the dose-response curves of 5-HT to the right but hardly affected the acetylcholine responses. Stimulating the anal part of SIII and SIV by 3–9 g balance weights via hook and pulley induced the contractions (0.2–2 g) of both oral and anal site (26.5% of trial) or one side of oral (50.0%) or anal site (23.5%) about 2–6 mm apart from the stimulated point. Intrinsic reflex arcs seem to operate in the caudal lamprey intestine. The intrinsic reflex responses were suppressed by about 50% in the presence of 14–29 μg/ml curare and suppressed by 80–100% in the presence of 20 μM spiperone or ketanserine. Atropine 20 μM had almost no inhibitory effects on the reflex. It was suggested that lamprey intestinal smooth muscles seem to have separate receptors for acetylcholine and 5-HT. Intrinsic reflex may be mediated both by cholinergic and serotonergic interneurones and more probably by serotonergic motoneurones. These characteristics of the lamprey were discussed by comparison with those of other vertebrate intestines.