THE DISTRIBUTION OF NEUROACTIVE SUBSTANCES WITHIN THE CERCARIA OF SANGUINICOLA-INERMIS

The serotoninergic and peptidergic components of the nervous system of the cercaria of Sanguinicola inermis (Digenea: Sanguinicolidae) were examined using whole-mount immunocytochemistry and a plan of the nervo us system has been described. Antibodies to serotonin (5-hydroxytrypta mine, 5-HT) and the neuropeptides, FMRFamide, GFNSALMFamide (S1) and S GPYSFNSGLTFamide (S2) were used in the study. Immunoreactivity (IR) wa s demonstrated to all but the S2 antisera and showed a similar fundame ntal distribution. IR was found in paired cerebral ganglia located ant eriorly within the body and connected by a cerebral commissure. From t he ganglia paired ventral and dorsal longitudinal nerve cords extend a nteriorly into the cephalic organ and into the body. There is no appar ent connection with the tail. Several transverse commissures connect t he longitudinal nerve cords throughout the body and several associated cell bodies have been located. A double-stranded dorsal and ventral l ongitudinal nerve cord extends the length of the tail and six cell bod ies are associated with these cords, uniquely demonstrating either FMR Famide and S1, or 5-HT-like IR. Only 5-HT-like IR was found to extend into the posterior tail furcae and there appears to be a lack of any p eripheral tegumental innervation. Double-labelling experiments suggest that the serotoninergic and peptidergic components of the cercarial n ervous system are distinct.