FMRFAMIDE-LIKE AND ALLATOSTATIN-LIKE IMMUNOREACTIVITY IN THE LATERAL HEART NERVE OF PERIPLANETA-AMERICANA - COLOCALIZATION AT THE ELECTRON-MICROSCOPIC LEVEL

Both allatostatin immunoreactivity (AS-IR) and FMRFamide immunoreactiv ity (FMRFa-IR) have been demonstrated light-microscopically in the lat eral heart nerve of Periplaneta americana. The identical labeling of s ome fibers suggests the coexistence of the two antigens. Electron-micr oscopically, six granule types in the peripheral part of the lateral h eart nerve can be distinguished according to their size and density (t ypes 1-6). These granule types can be subdivided immuno-cytochemically by means of a new mirror-section technique. Granules of types 4 and 5 always exclusively show FMRFa-IR. In the populations of fibers contai ning granules of types 1 and 6, axon profiles can be found that contai n granules colocalizing FMRFa-IR and AS-IR. Other axon profiles of the se populations only contain immunonegative granules of the same ultras tructure. Granules of type 2 can be differentiated immunocytochemicall y in three forms in the same section: In some fibers, they are nonreac tive; in other fibers of the same section, they show FMRFa-IR, whereas in a third fiber type, granules show AS - IR. Finally, granules of ty pe 3 can be observed with FMRFa-IR. In other fibers, they occur with t he same ultrastructure but exhibit no immunoreactivity. Two soma types occur in the lateral heart nerve. Soma type I is characterized by the production of electron-dense granules that show FMRFa-IR. Type II is in close contact with various fibers, forming different types of axoso matic synapses, hitherto unknown in In-secta.