KNEBEL, Stephanie M.; SAWYER, Sara; KRAJNIAK, Kevin G.; Southern Illinois Univ. Edwardsville: Investigation of serotonergic activity in the gizzard of Lumbricus terrestris: Serotonergic immunohistochemical localization

Serotonin is a biogenic amine that modulates smooth muscle contractions of the crop and gizzard of the earthworm, Lumbricus terrestris. Investigations into the nature of the serotonin receptor in the earthworm crop-gizzard suggest that the receptor is pharmacologically related to the mammalian type 2 receptor. The presence of serotonin in the worm central nervous system has been confirmed by immunohistochemistry, however its occurrence in the periphery has not been examined. In this study we investigated the immunohistochemical localization of this biogenic amine in the gizzard. Cryostat sections of gizzard were stained with an anti-serotonin antiserum and double stained with the nuclear stain Hoeschst. Serotonin immunoreactivity was seen in the circular and longitudinal muscle layers of the gizzard. The greatest intensity of staining was observed in the circular muscle layer, but this was also where the highest concentration of cell bodies was seen, as confirmed by nuclear staining. Thus we conclude that serotonin is present in both the longitudinal and circular smooth muscles. These data along with the pharmacological data suggest that serotonin is involved in the control of the earthworm digestive tract motility.