Age-related changes in parvalbumin- and GABA-immunoreactive cells in the rat septum.

The calcium binding protein parvalbumin is present in GABAergic neurons of the medial septum-diagonal band of Broca (MS-DBB) region that project to the hippocampal formation. We examined the distribution pattern, the number, and the morphological features of the parvalbumin-containing cells (parv+) in the MS-DBB region of 2- to 3-, 8- to 9-, 15- to 16-, and 26- to 27-month-old Sprague-Dawley rats. A significant reduction in the number of parv+ cells was observed as a function of age. The mean somal area of the parv+ cells was significantly reduced in the 26- to 27-month-old rats. A significant reduction in the number of parv+ cells was also observed in the 26- to 27-month-old rats in the cingulate cortex, but not in the striatum or the hippocampal formation. No significant age-related changes were observed in the number of the GABA-immunoreactive cells in the MS-DBB region nor in the cingulate cortex. In conclusion, there is an age-related decrease in the number of parv+ cells, with no change in the number of GABA-immunoreactive cells in the MS-DBB region of the rat. Because GABA and parvalbumin are colocalized in the MS-DBB neurons, the results suggest that the level of parvalbumin is decreased, but that the cells are not lost.