Immunohistochemical and biochemical detection of serotonin in the guinea pig celiac-superior mesenteric plexus.

Serotonin (5-HT) in the guinea pig celiac-superior mesenteric plexus was quantitatively measured by HPLC and visualized by an immunohistochemical method. Preincubation of the ganglia in a Krebs solution containing L-tryptophan and pargyline markedly elevated the content of 5-HT and K+ solution caused a release of 5-HT into the incubation medium. 5-HT immunoreactivity was localized to dense but unevenly distributed nerve fibers throughout the plexus and to small diameter cells commonly referred to as small intensely fluorescent cells. These findings provide evidence of an extensive network of 5-HT-containing neural elements in the guinea pig prevertebral ganglia.