Catecholamine-containing, serotonin-like and neuropeptide FMRFamide-like immunoreactive cells and processes in the nervous system of the pilidium larva (Nemertini)

Abstract

Pilidium larvae at different developmental stages have been investigated for the occurrence of glyoxylic acid induced fluorescence in catecholamines (CA), and serotonin-like (5-HT) and neuropeptide FMRFamide-like (FMRFamide) immunoreactivity (ir). The distribution of CA, 5-HT-ir and FMRFamide-ir cells and processes was compared with the location of nerve processes as found by transmission electron microscopy (TEM). In the pilidium larvae the marginal and oral nerves contain CA and 5-HT-ir processes and 5-HT-ir unipolar cells. The posterior suboral nerve contain CA and 5-HT-ir processes, whereas in the anterior suboral nerve neither CA nor 5-HT-ir and FMRFamide-ir were observed. The lateral helmet nerve contains FMRFamide-ir processes and unipolar cells. In the epidermis CA and 5-HT-ir multipolar cells were found. The juvenile “worm” that develops inside the pilidium larva was found to contain only 5-HT-ir. A pair of lateral cords extent the whole length of the juvenile and anteriorly they form the anterior ventral cerebral commissure. Also, from the anterior part of the lateral cords projects a pair of circumrhynchodeal processes which dorsally form the dorsal cerebral commissure. A pair of proboscis processes originate from the circumrhynchodeal processes and extend the whole length of the probosics. From the dorsal cerebral commissure cephalic processes project rostrally and ventrally. Only unipolar 5-HT-ir cells were observed, and they were located along the lateral cords into which their processes extend.