Protein S100 immunoreactivity in glial cells and neurons of the Japanese quail brain.

In mammals, sparse data illustrated the neuronal expression of S100 protein in central and peripheral nervous system. Similar studies have not been performed in other vertebrate species, in particular in birds. We provide here a detailed description of the distribution of the calcium-binding protein S100 in neuronal and glial elements in the central nervous system of an avian species, the Japanese quail (Coturnix japonica) largely used for neuroanatomical and functional studies. The distribution of S100-like immunoreactivity was analyzed by three different antisera: a polyclonal, against S100 protein, and two monoclonals, against the beta-subunit (S100beta) and the alpha-subunit (S100alpha) of this protein. All sera showed glial positive elements, which were more abundant in the brainstem than in the prosencephalon. Moreover, the polyclonal and the monoclonal antibodies against the beta-subunit evidenced a neuronal population with a wide distribution, variable morphology and staining intensity. In the telencephalon and diencephalon a few S100-positive neurons were observed in basal ganglia, nucleus paraventricularis hypothalami, nucleus rotundus and nucleus geniculatus lateralis, pars ventralis. In the mesencephalon and pons a wide S100-immunoreactive neuronal population was detected in several regions, including motor and sensory nuclei of most cranial nerves (i.e. oculomotoris, abducens, trigeminus, cochlearis, trochlearis and vestibularis nuclei). This distribution appears very similar to that previously described in the rat hindbrain by both immunocytochemistry and in situ hybridization, as well as to sparse observations on different vertebrates. Therefore, our results suggest that the distribution pattern of this protein (both in glial and in neuronal elements) is highly conserved throughout the phylogeny.