GAMMARUS-LACUSTRIS HARBORING POLYMORPHUS-PARADOXUS SHOW ALTERED PATTERNS OF SEROTONIN-LIKE IMMUNOREACTIVITY

The pattern of serotonin-like immunoreactivity in the central nervous system of individuals of the amphipod Gammarus lacustris harboring pol ymorphid cystacanths was compared to the pattern seen in individuals n ot infected with acanthocephalans. Ventral nerve cords from both paras itized and nonparasitized amphipods showed the same bilateral pair of immunoreactive cell bodies in the third thoracic ganglion. Significant differences were noted in the fine structure of these cell bodies, wi th nerve cords from Polymorphus paradoxus-parasitized amphipods showin g a greater number of bright spots or localized points of storage of s erotonin. The results of this study indicate that infection of G. lacu stris by cystacanths of P. paradoxus, but not P. marilis, is correlate d with changes in the anatomy of the serotonergic neurons of the amphi pod's central nervous system.