Changes in NADPH-diaphorase neurons of the rat laterodorsal and pedunculopontine tegmental nuclei in aging.

The aim of the present study was to compare the morphological pattern and the quantitative parameters of nitric oxide (NO)-containing neurons in the laterodorsal (LTD) and pedunculopontine (PPN) tegmental nuclei of 3-, 12- and 26-month-old rats. NADPH-diaphorase (NADPH-d) histochemical reaction, as a marker of the cholinergic neurons in the two mesopontine nuclei, and computer-assisted image analysis were used. The relationships between the neurons stained for NADPH-d and choline acetyltransferase (ChAT) were examined using a double-labelling procedure. The results demonstrated only occasional ChAT positive somata that did not exhibit NADPH-d staining. The volume of the LTD and PPN and the number of NADPH-d neurons remained unaltered with advancing age. However, ANOVA demonstrated a significant effect of age and level on the cross-sectional areas, maximum diameters and staining intensity of NADPH-d somata in the LTD and PPN. The three parameters were reduced in 26-month-old rats compared to 3-month-old rats. The changes in the morphological appearance of NADPH-d somata and processes as well as the quantitative analysis pointed to age-related neuronal atrophy. It was accompanied by hypertrophy of some neighbouring neurons, suggesting a compensatory mechanism which would counteract the degenerative changes. The age-dependent alterations in the LTD and PPN were rather similar.