Venous mechanoreceptor input to neurones in the inferior mesenteric ganglion of the guinea-pig.

Intracellular recordings were made in vitro from neurones of guinea-pig inferior mesenteric ganglia (i.m.g.) attached to the mesenteric vasculature of the distal colon region. The inferior mesenteric vein was cannulated for distension. Non-evoked continuous excitatory post-synaptic potentials (e.p.s.p.s) and action potentials were recorded from 38% of neurones in the absence of the colon or any imposed perturbation. Continuous e.p.s.p.s were blocked by hexamethonium, tetrodotoxin and by transection of the lumbar colonic nerves. Distension of the inferior mesenteric vein altered the frequency of continuous activity in 23% of cells which exhibited continuous activity. Venous distension was associated with a depolarization in 31% of cells tested. The depolarization averaged 2.8 mV and in 89% of these was associated with an increase in membrane resistance. A further 14% of cells exhibited an increase in membrane resistance in the absence of depolarization. Venous distension increased the amplitude of fast e.p.s.p.s generated by stimulation of the lumbar splanchnic nerve or the intermesenteric nerve in 38% of cells tested. The results of this study demonstrate the existence of a mechanosensory pathway from the venous bed of the distal mesenteric region to the i.m.g. of the guinea-pig and suggest that distension may enhance neural transmission by increasing the excitability of ganglionic cells.