Ultrastructural examination of the targets of serotoninn immunoreactive descending interneurons in the guinea pig small intestine

Abstract

Serotonin neurons are descending interneurons in the myenteric plexus of the guinea pig small intestine. Preembedding single‐ and double‐label immunocytochemistries at the ultrastructural level were used to identify the targets of these serotonin interneurons. Serial ultrathin sections were taken through a myenteric ganglion that had been processed for serotonin immunocytochemistry. The ganglion contained the cell bodies of 69 neurons, including 2 serotonin neurons and 6 neurons with the ultrastructural features of Dogiel type II cells. For each cell body in the ganglion, the number of serotonin inputs (synapses and close contacts) was determined. About 50% of the cell bodies did not receive..