Localization and release of FMRFamide-like immunoreactivity in the cerebral neuroendocrine system of Manduca sexta

The distribution of FMRFamide-like immunoreactivity (FLI) in the cerebral neuroendocrine system of the moth, Manduca sexta, is described and evidence is provided for calcium-dependent release of FLI from the neurohaemal organs. FLI was detected by indirect immunofluorescence in approximately 25 bilaterally symmetrical pairs of somata in the pupal protocerebrum. In addition, FLI was observed in neurites in the brain, as well as in axons of the nervi corporis cardiaci and nervi corporis allati, and in terminals in the neurohaemal corpora cardiaca (CC) and corpora allata (CA). All immunocytochemical staining was blocked by preabsorption of the anti-FMRFamide antiserum with synthetic FMRFamide. We localized FLI to identified protocerebral neurosecretory cells (NSCs) by combining intracellular injection of Lucifer Yellow and indirect immunofluorescence. Among the NSCs in each hemisphere, FLI was observed in both group IIa (lateral) cells, in most group IIb (lateral) cells, and in two cells of group Ib (medial). FLI was extracted from the brain and neurohaemal organs and measured using radioimmunoassay (RIA). Calcium-dependent release of FLI was evoked from isolated CC-CA by high potassium depolarization in vitro and was quantified by RIA of the bathing medium. These results suggest that FLI may have a neurohormonal or neurotransmitter function in Manduca.