Influence of long-term treatment with L-deprenyl on the age-dependent changes in rat brain microanatomy

The present study was designed to assess whether treatment with the monoamine oxidase-B (MAO-B) inhibitor L-deprenyl, which has been documented to increase both mean and maximum survival in aged rats as well as sexual performance and cognitive function, has any effect on the age-related microanatomical changes occurring in the rat brain. Male Sprague-Dawley rats received a subcutaneous injection of 0.25 mg/kg L-deprenyl every other day from the 19th to the 24th month of age. Age-matched control rats were injected with saline, whereas 11-month-old untreated rats were used as an adult reference group. Both body and brain weight were increased as a function of age, and they were unaffected by treatment with L-deprenyl. The density of nerve cell profiles in the frontal cortex, in the CA-1 and CA-3 subfields of the hippocampus, in the dentate gyrus and in the cerebellar cortex were decreased in aged rats in comparison with adult rats. The density of nerve cell profiles in the above brain areas of L-deprenyl-treated rats was not significantly higher in comparison with age-matched control animals with the exception of Purkinje neuron profiles. The intensity of Nissl's staining, which may be related to the protein synthetic capabilities of nerve cells, is reduced within pyramidal neurons of the hippocampus and Purkinje neurons of the cerebellar cortex of aged rats. The intensity of Nissl's staining in L-deprenyl-treated rats was not different from adult rats. Lipofuscin deposition was significantly increased within the cytoplasm of pyramidal neurons of the frontal cortex, of the CA-3 subfield of the hippocampus and of Purkinje neurons of the cerebellar cortex. L-Deprenyl administration decreased lipofuscin accumulation within the cytoplasm of the above mentioned nerve cell types. The density of sulphide-silver staining in the intrahippocampal pathway of mossy fibres, which participate in the elaboration of passive avoidance responses, is decreased in aged rats. Treatment with L-deprenyl counters this age-related reduction. The above results suggest that long-term treatment with L-deprenyl is able to counter the expression of some microanatomical changes typical of aging brain.