Convergence of noncholinergic afferent neurons in the inferior mesenteric ganglion of the guinea pig

The pattern of noncholinergic innervation of principal ganglionic neurons from the lumbar colonic nerve (LCN) and lumbar splanchnic nerve (LSN) in the inferior mesenteric ganglion (IMG) of the guinea pig was studied with intracellular techniques. Simultaneous stimulation of the LCN and LSN at maximum frequency (20 Hz) and submaximal stimulus voltages (2-4 V) led to summation of slow excitatory postsynaptic potential (EPSPs) indicating convergence of neural input. Summation was observed with submaximal (but not maximal) stimulation parameters in cells with either large or small amplitude maximum slow EPSPs suggesting that each neuron has an individual maximum capacity to depolarize in response to non-cholinergic transmitter substances. The study indicates that neurons originating at both peripheral and central sites converge onto principal ganglionic neurons, thus these ganglionic neurons must perform a significant integrative function in the IMG.