Use of targetable gfp-tagged neuropeptide for visualizing neuropeptide release following execution of a behavior.

Previous work has shown that a transgene consisting of a fusion between the rat atrial natriuretic peptide and a green fluorescent protein reporter (ANF-gfp) is processed, localized, and released, as would be an endogenous neuropeptide when it is expressed in the nervous system of Drosophila melanogaster using the GAL4/UAS expression system. Here we have tested the utility of this targetable transgene for detecting neuropeptide release following the execution of a peptide-controlled behavior. For the behavior we used ecdysis, the behavior expressed by insects to shed their old cuticle at the end of the molt. We found that larval ecdysis was accompanied by a readily detectable reduction in gfp fluorescence from relevant secretory cells in the periphery and peptidergic neurons in the CNS. We also found that expression of the ANF-gfp products did not have detrimental effects on larval ecdysis or adult circadian rhythmicity, when the transgene was expressed in peptidergic cells that are known to control these behaviors. Finally, we used a broadly expressed GAL4 driver to show that the UAS-ANF-gfp transgene could be used to identify axons that show a reduction in gfp fluorescence following the expression of ecdysis behavior. These findings, coupled with the availability of an increasing number of strains bearing different GAL4 drivers, suggest that this transgene will be a useful tool for identifying peptidergic neurons and secretory cells (and, eventually, their secretory product) that release their peptide content during the occurrence, in the intact animal, of a developmental, physiological or behavioral process of interest.