GALANIN IMMUNOREACTIVE NEURONS IN THE MEDULLA-OBLONGATA OF RATS

The distribution of galanin-immunoreactive (-ir) neurons in the medull a oblongata was mapped with light microscopic immunohistochemistry. No immunopositive perikarya were seen in untreated rats. Two days after colchicine treatment, galanin immunopositive 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 territo ry of the catecholaminergic groups and in the peritrigeminal subdivisi on of the lateral reticular nucleus; 3) vagal nuclei (nucleus of the s olitary tract, nucleus ambiguous); 4) two cell groups at the ventral s urface of the rostro-caudal middle portion of the medulla oblongata (t hey do not correspond to any known demarkated anatomical nuclei, but r elated to the chemosensitive medullary area); 5) in the gelatinous par t of the spinal trigeminal nucleus. The wide distribution of galanin n eurons 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 res toration of lesioned neurons (nerve growth factor-like activity). An i ncreased galanin mRNA expression can be seen in dorsal vagal or hypogl ossal motor neurons after intracranial transections of vagal or hypogl ossal nerves, respectively. Transections of the olivocerebellar tract induced galanin gene expression in neurons of the contralateral inferi or olive. After brainstem hemisection, galanin immunopositivity was se en in cells of the nucleus of the solitary tract due to the transectio n of ascending projections of this primary autonomic center in the med ulla oblongata.