Morphological evidence for effects of the aging on the serotoninergic neurons in the rat brainstem nuclei

The effects of age on the 5-hydroxytryptamine-immunoreactive (5-HT-IR) neurons in raphe and extrarapheal nuclei of rats were examined using morphometry. Quantitative parameters of the neuronal density and cross-sectional areas of the cell bodies as well as of the length and numbers of the processes of the 5-HT-IR neurons were analyzed in 3-, 12- and 26-month-old-rats. The results showed that aging affected the 5-HT-IR neurons in the rat brainstem nuclei. The age-related changes in the immunostaining pattern and quantitative parameters were more or less pronounced and earlier or later developed depending on the nucleus studied. It is most probably connected with specific functions and projections of each raphe nucleus.