Age-related changes in sulfide-silver stainable fibres in the rat cerebral cortex

The present study was designed to assess the age-dependent changes in sulfide-silver stainable fibres in frontal, parietal and occipital cortex areas of the rat cerebral cortex. Male Sprague-Dawley rats of 2 months (young), 12 months (adult) and 24 months (aged) were used. Sulfide-silver stainable fibres, which represent predominantly zinc-containing associational fibres arising from local cortical interneurons, were visualized using the neo-Timm histochemical technique. The density of sulfide-silver stainable fibres within the neuropil of laminae I-III (upper zone) and of lamina V (lower zone) of the different cerebral cortex areas was assessed microdensitometrically. In the frontal and parietal cortices the density of sulfide-silver stainable fibres was higher in adult and in aged than in young rats both in the upper and in the lower zones. No significant differences were noticeable in the density of sulfide-silver stainable fibres between adult and old rats. In the occipital cortex the density of sulfide-silver stainable fibres was similar in young or adult rats. but was remarkably increased in old animals. The possibility that the increase in the density of sulfide-silver stainable fibres represents a compensatory mechanism in the cerebral cortex area showing the most consistent nerve cell loss is discussed.