Galanin immunoreactivity in the blowfly nervous system: Localization and chromatographic analysis
Authors: Lundquist C. Tomas , Rökaeus Åke , Nässel Dick R. 
Published: January 2005

In this study chromatographic, immunochemical, and immunocytochemical methods provide evidence of a galanin‐like peptide(s) in an invertebrate, the blowfly Phormia terraenovae. The major portion of the galanin‐like immunoreactivity (GAL‐LI) in fly heads was extractable in acetic acid but not in boiling water, which suggests that the peptide(s) may be highly basic in nature. GAL‐LI was present both in the head and body portion of the blowfly in roughly the same amounts. Initial gel filtration data, using a G‐50 Sephadex column and a weak phosphate‐buffer (pH 6.5) as eluent, suggested that a fly GAL‐LI peptide(s) from fly heads, eluting as an apparent single peak, was smaller than porcine GAL(1–29) and GAL(1–15). However, concomitant analysis using a G‐25 Sephadex column and acetic acid (0.2 M) as eluent, spread the immunoreactive material over a great portion of the chromatogram, although the main portion of the material eluted in the same size range as porcine GAL(1–29). Taken together, the gel filtration data thus suggest that fly GAL‐LI peptide(s) may be highly basic but presumably similar in size to vertebrate GAL(1–29). However, the hydrophobic properties of the fly GAL‐LI peptide(s) differ from that of porcine GAL as demonstrated by the presence of several immunoreactive components eluting both early as well as late in the chromatogram when using reverse‐phase high performance liquid chromatography (HPLC); early peaks may represent highly basic and/or possibly smaller GAL‐immunoreactive peptide(s), whereas later peaks may represent less basic and possibly elongated forms.

Immunocytochemistry indicated that GAL‐LI was present in the nervous system of the blowfly. About 160 GAL‐immunoreactive neurons were found in the brain and subesophageal ganglion, 26 in the fused thoracic ganglion and 30 in the fused abdominal ganglion. In the brain, GAL‐immunoreactive fibers supply specific subdivisions of the central body, optic lobe, superior protocerebrum, and tritocerebrum as well as neuropil in the subesophageal ganglia. In the thoracico‐abdominal ganglia, GAL‐immunoreactive neuron processes are found inside synaptic neuropil as well as in the neural sheath of the ganglia and several of the dorsal nerve roots. Many of the GAL‐immunoreactive neurons react also with an antiserum against porcine galanin message associated peptide, a peptide present in the preprogalanin protein. Immunocytochemical double‐labeling indicated that some GAL‐immunoreactive neurons also reacted with antisera against the molluscan peptides FMRFamide and SCPB, whereas no evidence could be found for colabeling with antisera against, tyrosine hydroxylase, substance P and physalaemin.

The GAL‐like peptide(s) may have diverse functions in the blowfly nervous system similar to findings in the mammalian nervous system. A role as a neuromodulator in the central nervous system and a neurohormone acting on peripheral targets such as skeletal and possibly visceral muscles and salivary glands may be suggested.