Choline acetyltransferase immunoreactive sympathetic ganglion cells in a teleost, Stephanolepis cirrhifer

The present study showed neurons immunoreactive for choline acetyltransferase (ChAT) in the cranial sympathetic ganglia lying close to the trigeminal–facial nerve complex of the filefish. In these ganglia, less than 1% of ganglion cells were positive for choline acetyltransferase. Choline acetyltransferase-positive neurons were significantly larger than the randomly sampled neurons in this ganglion. The majority of choline acetyltransferase-positive neurons were negative for tyrosine hydroxylase, but many of them were positive for galanin (GAL). Some neurons were positive for both choline acetyltransferase and tyrosine hydroxylase, but these neurons were rarely immunoreactive for dopamine β hydroxylase, suggesting that they are not adrenergic. In the cranial sympathetic ganglia and the celiac ganglia, many nerve fibers immunoreactive for galanin were seen, and varicose terminals were in contact selectively with neurons negative for both choline acetyltransferase and tyrosine hydroxylase, but not with those positive for choline acetyltransferase or tyrosine hydroxylase. Nerve fibers immunoreactive for choline acetyltransferase were found to be present in contact with the deep layer of chromatophores, which was observed only in the labial region. These results suggest that cholinergic postganglionic neurons are present in the filefish cranial sympathetic ganglia, and that they also contain galanin. As few cholinergic sympathetic neurons express tyrosine hydroxylase and none express dopamine β hydroxylase, they are unlikely to synthesize noradrenaline or adrenaline.