Age-related loss of galanin-immunoreactive cells in the rat septal area.

We have examined the distribution of galanin-like immunoreactive (LI) cell bodies in the medial septal nucleus (MS) and the nucleus of the diagonal band of Broca (nDBB) of young (3 months) and aged (25-30 months) rats, and assessed their respective contribution to the septohippocampal pathway. Immunohistochemical techniques were used alone or combined with the retrograde transport of a protein-gold complex injected into the dorsal hippocampus. In both groups, galanin-LI cells were observed in the MS and the nDBB. In aged rats, a significant decrease in both the staining intensity and the number of galanin-LI perikarya throughout the MS-nDBB complex was observed. Some immunoreactive cells appeared shrunken. The reduction in cell number ranged from 30 to 85%. There was also a decrease in the proportion of septohippocampal neurons containing galanin in aged rats (13% vs 20% in young animals) which however did not reach statistical significance. These results suggest that galanin-positive cells in the medial septal area undergo alterations with aging in the rat.