SEROTONIN-IMMUNOREACTIVITY IN PERIPHERAL-TISSUES OF THE OPISTHOBRANCHMOLLUSKS PLEUROBRANCHAEA-CALIFORNICA AND TRITONIA-DIOMEDEA

The distribution of serotonin (5-HT)-immunoreactive elements in periph eral organs of the sea-slugs Pleurobranchaea californica and Tritonia diomedea was studied in cryostat sections. For Pleurobranchaea, 5-HT-i mmunoreactive (5-HT-IR) neuron cell bodies were found only in the cent ral nervous system (CNS); 5-HT-IR cell bodies were not observed in foo t, tentacles, rhinophores, oral veil, mouth, buccal mass, esophagus, g ills, salivary glands, skin, reproductive system, and acidic glands, n or in peripheral tentacle and rhinophore ganglia. However, 5-HT-IR neu ronal processes were widely distributed in these structures and the pa tterns of 5-HT-IR elements were characteristic for each particular per ipheral tissue. 5-HT-IR elements were most dense in the sole of the fo ot and the reproductive system, followed by rhinophores, tentacles, or al veil, mouth, buccal mass, and esophagus. The sensory epithelium of rhinophores, tentacles, and mouth showed a highly structured glomerula r organization of 5-HT-IR fibers, suggesting a role for 5-HT in sensor y signaling. A much lower density of 5-HT-IR innervation was observed in gills, skin, salivary, and acidic glands. 5-HT-IR was observed in n europil of tentacle and rhinophore ganglia with many transverse 5-HT-I R axons running to peripheral sensory areas. The distribution of 5-HT- IR elements in Tritonia was similar to that of Pleurobranchaea. A sign ificant suggestion of the data is that central serotonergic neurons ma y modulate afferent pathways from sensory epithelia at the periphery. (C) 1997 Wiley-Liss, Inc.