CHARACTERIZATION OF MYENTERIC INTERNEURONS WITH SOMATOSTATIN IMMUNOREACTIVITY IN THE GUINEA-PIG SMALL-INTESTINE

The projections, connections, morphology and electrophysiological feat ures of the myenteric interneurons with somatostatin immunoreactivity in the guinea-pig small intestine have been established using retrogra de tracing immunohistochemistry, confocal microscopy and intracellular recording. After application of the fluorescent dye, 1,1'-didodecyl-3 ,3,3',3'-tetramethyl indocarbocyanine perchlorate (DiI), to the myente ric plexus, up to 900 nerve cell bodies were labelled in each preparat ion. Somatostatin-immunoreactive neurons accounted for 13% of all retr ogradely labelled cells and were located up to 70 mm orally. When DiI was applied to the submucous ganglia, many myenteric neurons were labe lled and 8% of all retrogradely labelled cells were somatostatin immun oreactive and were located up to 60 mm oral to the DiI application sit es. These neurons had ovoid cell bodies, a single axon, several long f ilamentous dendrites and received close contacts from 40-200 somatosta tin-immunoreactive varicosities. Intracellular recordings revealed tha t these cells had Features of both S (i.e. with Synaptic inputs) and A H (i.e. neurons with After Hyperpolarization) cells, receiving fast ex citatory synaptic inputs, having characteristic ''sag'' in their respo nse to hyperpolarizing current pulses and sometimes a long afterhyperp olarization following soma action potentials. It is concluded that som atostatin-immunoreactive neurons have distinct electrophysiological fe atures and form very long anally directed interneuronal chains that co nnect with both myenteric and submucous neurons. (C) 1997 IBRO. Publis hed by Elsevier Science Ltd.