Calretinin immunoreactivity in the brain of the zebrafish, Danio rerio:: Distribution and comparison with some neuropeptides and neurotransmitter-synthesizing enzymes.: II.: Midbrain, hindbrain, and rostral spinal cord

The distribution of calretinin (CR) in the brainstem and rostral spinal cord of the adult zebrafish was studied by using immunocytochemical techniques. For analysis of some brainstem nuclei and regions, CR distribution was compared with that of complementary markers (choline acetyltransferase, glutamic acid decarboxylase, tyrosine hydroxylase, neuropeptide Y). The results reveal that CR is a marker of various neuronal populations distributed throughout the brainstem, including numerous cells in the optic tectum, torus semicircularis, secondary gustatory nucleus, reticular formation, somatomotor column, gustatory lobes, octavolateral area, and inferior olive, as well as of characteristic tracts of fibers and neuropil. These results indicate that CR may prove useful for characterizing a number of neuronal subpopulations in zebrafish. Comparison of the distribution of CR observed in the brainstem of zebrafish with that reported in an advanced teleost (the gray mullet) revealed a number of similarities, and also some interesting differences. Our results indicate that many brainstem neuronal populations have maintained the CR phenotype in widely divergent teleost lines, so CR studies may prove very useful for comparative analysis.