Calretinin expression in specific neuronal systems in the brain of an advanced teleost, the grey mullet (Chelon labrosus).

Abstract

The distribution of calretinin (CR) in the brain of an "advanced" teleost, the grey mullet, was studied by using immunoblotting and immunocytochemical techniques. In immunoblots of protein extracts of rat and mullet brains, the CR antibody stained a single band of about 29 kDa. CR immunoreactivity was observed in specific neuronal populations of all brain regions. The primary olfactory system, the optic nerve fibers, and some sensory fibers of other cranial nerves exhibited strong CR immunoreactivity. In the forebrain, the CR-immunoreactive (CR-ir) populations were scarce in the telencephalon and hypophysiotrofic hypothalamus, but numerous in many specialized nuclei of the diencephalon (preglomerulosus complex, nucleus glomerulosus, anterior glomerular nucleus, nucleus diffusus) and pretectum (parvocellular and magnocellular superficial pretectal nuclei, central pretectal nucleus), which are related to sensory systems. The two main forebrain bundles, medial and lateral, contained numerous CR-ir fibers. The midbrain sensory centers (optic tectum and torus semicircularis) exhibited numerous CR-ir cells and fibers. Likewise, the secondary gustatory nucleus of the isthmus is one of the nuclei exhibiting more intense CR immunoreactivity. Characteristically, the efferent cerebellar system (eurydendroid cells and brachium conjunctivum) and some afferent cerebellar fibers were CR-ir. In the medulla oblongata, a number of reticular cells, the inferior olive, and the magnocellular octaval nucleus exhibited CR immunoreactivity. CR-ir motoneurons were also observed in the spinal cord and in the oculomotor nucleus. Together with results obtained in other vertebrates, present results suggest that neural systems using calretinin to maintain intracellular calcium concentration have been rather well conserved during vertebrate evolution.