Localization of pigment-dispersing hormone (PDH) immunoreactivity in the central nervous system of Carcinus maenas and Orconectes limosus (Crustacea), with reference to FMRFamide immunoreactivity in O. limosus.

By use of antisera raised against synthetic pigment-dispersing hormone (PDH) of Uca pugilator and FMRFamide, the distribution of immunoreactive structures in the central nervous system (CNS) of Carcinus maenas and Orconectes limosus was studied by light microscopy. In both species, a total of 10-12 PDH-positive perikarya occur amongst the anterior medial, dorsal lateral and angular somata of the cerebral ganglion (CG). In C. maenas, one PDH-perikaryon was found in each commissural ganglion (COG) and several more in the thoracic ganglion. In O. limosus, only four immunopositive perikarya could be demonstrated in the ventral nerve cord, i.e., two somata in the anterior and two in the posterior region of the suboesophageal ganglion (SOG). PDH-immunoreactive tracts and fiber plexuses were present in all central ganglia of both species, and individual axons were observed in the connectives. FMRFamide-immunoreactivity was studied in O. limosus only. Neurons of different morphological types were found throughout the entire CNS, including numerous perikarya in the anterior medial, anterior olfactory, dorsal lateral and posterior cell groups of the CG. Four perikarya were found in the COG, six large and numerous smaller ones in the SOG, and up to eight cells in each of the thoracic and abdominal ganglia. In each ganglion, the perikarya form fiber plexuses. Axons from neurons belonging to the CG could be traced into the ventral nerve cord; nerve fibers arising from perikarya in the SOG appeared to project to the posterior ganglia. In none of the structures examined colocalization of PDH- and FMRF-amide-immunoreactivity was observed.