Tachykinin-related neuropeptide in the crayfish olfactory midbrain

Immunoreactivity indicative of tachykinin-related peptide (TRP) was detecte d in the olfactory midbrain of the crayfish Pacifastacus leniusculus when u sing an antiserum to the insect neuropeptide locustatachykinin I (Lom-TK-I) . A monoclonal antibody to the mammalian tachykinin substance P was shown i n double-labeling experiments to label structures in the crayfish brain ide ntical to those labeled with the LomTK antiserum. Within the midbrain LomTK -like immunoreactive (LomTK-LI) material was observed in a limited populati on of neuronal somata and their varicose processes. A single pair of large interneurons gave rise to numerous varicose LomTK-LI processes innervating a cluster of cell bodies (cluster 10) as well as the olfactory neuropils. T he latter neuropil was also innervated by a population of LomTK-LI globuli cells with cell bodies in cluster 9. Radioimmunoassay (RIA), utilizing the LomTK antiserum, and reverse-phase high-performance liquid chromatography ( HPLC) were used to partially characterize the immunoreactive material in ex tract of the portion of the midbrain that houses the olfactory (OL) and acc essory (AL) lobes and cell clusters 9 and 10 on the one hand, and in extrac t of the remaining parts of the brain on the other. Approximately the same amounts of LomTK-LI material were observed for the two extracts. RIA showed that the immunoreactive material of both extracts diluted roughly in paral lel to synthetic LomTK-I and HPLC analysis of the extracts revealed immunor eactive material in both tissues which eluted with retention times in the r ange of synthetic LomTK-I and LomTK-II. These results suggest that TRPs sim ilar to LomTKs are present in the olfactory midbrain of Pacifastacus. The d istribution of immunolabeled neuronal structures suggests that in the crayf ish, peptide(s) closely related to insect TRPs may act as a neuroactive sub stance released from nerve fibers in olfactory neuropil areas and at certai n neuronal cell bodies.