NEUROCHEMICAL ALTERATIONS BUT NOT NERVE-CELL LOSS IN AGED RAT NEOSTRIATUM

Numerical changes in the overall neostriatal neuronal population have been investigated by morphometric analysis of Nissl-stained and glucoc orticoid receptor-immunoreactive neurons. Number and staining intensit y of various chemically-identified nerve cell populations were analyse d by means of immunocytochemistry coupled with computer-assisted image analysis. Three- and 24-month-old male Sprague-Dawley rats were used. No change in the number of Nissl-stained, glucocorticoid receptor-, d opamine and adenosine 3':5'-monophosphate-regulated phosphoprotein- an d enkephalin-immunoreactive neurons and a 50% decrease of neuropeptide Y-immunoreactive neurons were observed in the aged rat. In our prepar ations. the glucocorticoid receptor antibody stains around 90% of the neostriatal neurons, the dopamine and adenosine 3':5'-monophosphate-re gulated phosphoprotein and enkephalin antibodies label 25-35% and the neuropeptide Y- antibody stains only 1% of neostriatal neurons. In the same preparations a significant decrease in the intensity of immunost aining was observed for enkephalin-, dopamine and adenosine 3':5'-mono phosphate-regulated phosphoprotein- and neuropeptide Y-immunoreactive neuronal cell bodies and tyrosine hydroxylase-immunoreactive nerve ter minals in the aged rat. In the case of neuropeptide Y-, and dopamine a nd adenosine 3':5'-monophosphate-regulated phosphoprotein-immunoreacti ve neurons, the changes in the intensity of immunostaining were differ entially compartmentalized within neostriatum, suggesting selective vu lnerability of striatal subregions to ageing processes. In conclusion, these data indicate that no significant age-related neuronal cell los s occurs in neostriatum. On the other hand, a generalized decrease in the levels of peptide transmitters and molecules related to dopamine t ransmission is observed in aged rat neostriatum, possibly resulting in the known age-related deficits of neostriatally-controlled behaviours .