Major species variation in the expression of galanin messenger ribonucleic acid in mammalian celiac ganglion.

To determine whether galanin may be a sympathetic neurotransmitter in the pancreas of primates and rats as well as dogs, the expression of the galanin gene was examined in the celiac ganglion of these species by in situ hybridization and RIA. Intense hybridization signal for galanin messenger RNA (mRNA) was observed in every neuronal cell body of the dog celiac ganglion. However, significant hybridization signal for galanin mRNA was seen in only 24 +/- 5% of celiac ganglion cell bodies in monkeys and was absent in rats. RIA of celiac ganglion extracts confirmed this species variation; galanin-like immunoreactivity was highest in dog celiac ganglion (158 +/- 13 pmol/g), present in monkeys (34 +/- 7 pmol/g), and undetectable in rats (< 0.8 pmol/g). In contrast, the celiac ganglia of all three species showed intense hybridization signal for neuropeptide-Y (NPY) mRNA in the majority of neuronal cell bodies (dog, 82 +/- 4%; monkey, 92 +/- 2%; rat, 91 +/- 3%), and the celiac ganglion NPY immunoreactivity content was high in all three species (dog, 1064 +/- 155 pmol/g; monkey, 3180 +/- 745 pmol/g; rat, 3412 +/- 347 pmol/g). Thus, there is a marked species variation in the expression of the galanin, but not the NPY, gene in the celiac ganglion of dogs, monkeys, and rats. These data suggest that galanin is an important sympathetic neurotransmitter in the pancreatic islets of dogs, but not those of primates or rats.