PUTATIVE NEUROHEMAL AREAS IN THE PERIPHERAL NERVOUS-SYSTEM OF AN INSECT, GRYLLUS-BIMACULATUS, REVEALED BY IMMUNOCYTOCHEMISTRY

The morphology and position of putative neurohemal areas in the periph eral nervous system (ventral nerve cord and retrocerebral complex) of the cricket Gryllus bimaculatus are described. By using antisera to th e amines dopamine, histamine, octopamine, and serotonin, and the neuro peptides crustacean cardioactive peptide, FMRFamide, leucokinin 1, and proctolin, an extensive system of varicose fibers has been detected t hroughout the nerves of all neuromeres, except for nerve 2 of the prot horacic ganglion. Immunoreactive varicose fibers occur mainly in a sup erficial position at the neurilemma, indicating neurosecretory storage and release of neuroactive compounds. The varicose fibers are project ions from central or peripheral neurons that may extend over more than one segment. The peripheral fiber varicosities show segment-specific arrangements for each of the substances investigated. Immunoreactivity to histamine and octopamine is mainly found in the nerves of abdomina l segments, whereas serotonin immunoreactivity is concentrated in sube sophageal and terminal ganglion nerves. Immunoreactivity to FMRFamide and crustacean cardioactive peptide is widespread throughout all segme nts. Structures immunoreactive to leucokinin 1 are present in abdomina l nerves, and proctolin immunostaining is found in the terminal gangli on and thoracic nerves. Codistribution of peripheral varicose fiber pl exuses is regularly seen for amines and peptides, whereas the colocali zation of substances in neurons has not been detected for any of the n euroactive compounds investigated. The varicose fiber system is regard ed as complementary to the classical neurohemal organs.