Substance P Binding Sites in Guinea-Pig Enteric Ganglia

There is convincing evidence that substance P (SP) is an excitatory neurotransmitter to the muscle of the mammalian gastrointestinal tract [1]. SP also promotes water and electrolyte secretion across the mucosa of the small intestine of the guinea-pig, in vitro, and this effect is largely due to excitation of the secretomotor neurons in the submucosa [2]. Submucous neurons are surrounded by SP immunoreactive varicosities [3]. Many of these neurons are depolarized by SP via a mechanism similar to that responsible for the slow excitatory synaptic potentials that can be evoked in the same neurons by electrical stimulation of the internodal strands [4,5]. These results have led to the suggestion that SP mediates the slow excitatory synaptic potentials [4].