Galanin immunoreactive neurons in the medulla oblongata of rats.

The distribution of galanin-immunoreactive (-ir) neurons in the medulla oblongata was mapped with light microscopic immunohistochemistry. No immunopositive perikarya were seen in untreated rats. Two days after colchicine treatment, galanin immuno-positive neurons were localized in the following areas: 1) raphe nuclei (magnus, pallidus and obscurus); 2) in various parts of the reticular formation, mainly in the territory of the catecholaminergic groups and in the peritrigeminal subdivision of the lateral reticular nucleus; 3) vagal nuclei (nucleus of the solitary tract, nucleus ambiguous); 4) two cell groups at the ventral surface of the rostro-caudal middle portion of the medulla oblongata (they do not correspond to any known demarkated anatomical nuclei, but related to the chemosensitive medullary area); 5) in the gelatinous part of the spinal trigeminal nucleus. The wide distribution of galanin neurons in the medulla support data that had been reported on the role of this peptide in various viscerosensory and autonomic mechanisms. In addition to these, galanin seems to be an important factor in the restoration of lesioned neurons (nerve growth factor-like activity). An increased galanin mRNA expression can be seen in dorsal vagal or hypoglossal motor neurons after intracranial transections of vagal or hypoglossal nerves, respectively. Transections of the olivocerebellar tract induced galanin gene expression in neurons of the contralateral inferior olive. After brainstem hemisection, galanin immunopositivity was seen in cells of the nucleus of the solitary tract due to the transection of ascending projections of this primary autonomic center in the medulla oblongata.