Excitatory synaptic inputs on myenteric Dogiel type II neurones of the pigileum

The synaptic input on myenteric Dogiel type II neurones (n = 63) obtained f rom the ileum of 17 pigs was studied by intracellular recording. In 77% of the neurones, electrical stimulation of a fibre tract evoked fast excitator y postsynaptic potentials (fEPSPs) with an amplitude of 6 +/- 5 mV (mean +/ - S.D.) and lasting 49 +/- 29 ms. The nicotinic nature of the fEPSPs was de monstrated by superfusing hexamethonium (20 muM). High-frequency stimulatio n (up to 20 Hz, 3 seconds) did not result in a rundown of the fEPSPs, and d id not evoke slow excitatory or inhibitory postsynaptic potentials. The eff ects of neurotransmitters, possibly involved in these excitatory responses, were investigated. Pressure microejection of acetylcholine (10 mM in pipet te) resulted in a fast nicotinic depolarisation in 67%(18/27) of the neuron es (13 +/- 9 mV, duration 7.0 +/- 7.2 seconds) as did 1,1-dimethyl-4-phenyl piperazinium iodide (DMPP) application (10 mM; 14 +/- 10 mV, duration 4.1 /- 2.8 seconds) in 76%of the cells. The fast nicotinic response to acetylch oline was sometimes (6/27) followed by a slow muscarinic depolarisation (8 +/- 4 mV; duration 38.7 +/- 10.8 seconds). Immunostaining revealed 5-hydrox ytryptamine hydrochloride (5-HT)- and calcitonin gene-related peptide (CGRP )-positive neuronal baskets distributed around and in close vicinity to Dog iel type II neuronal cell bodies. Microejection of 5-HT (10 mM) resulted in a fast nicotinic-like depolarisation (12 +/- 6 mV, duration 3.0 +/- 1.3 se conds) in 4 of 8 neurones tested, whereas microejection of CGRP (20 mM) gav e rise to a slow muscarinic-like depolarisation (6 +/- 2 mV, duration 56.0 +/- 27.5 seconds) in 8 of 12 neurones tested. In conclusion, myenteric Dogi el type II neurones in the porcine ileum receive diverse synaptic input. Ma inly with regard to the prominent presence of nicotinic responses, these ne urones behave contrary to their guinea pig counterparts. J. Comp. Neurol. 4 32:137-154, 2001. (C) 2001 Wiley-Liss, Inc.