Ageing has a differential effect on nitric oxide synthase-containing and catecholaminergic amacrine cells in the human and rat retina.

In this study, we assessed the effects of normal ageing on the number, distribution, and somal area of nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-positive (NADPHd+) and tyrosine hydroxylase-immunoreactive (TH-IR) amacrine cells in human and rat retina. By using a double-labelling immunohistochemical technique, we have shown that these two enzymes are located in separate amacrine cell populations in the human retina. In normal human retinas from organ donors, we have shown that there was no change in the number, somal area, or retinal distribution of NADPHd+ neurons over an age range of 19-89 years. In contrast, there was a significant decrease (P < 0.05) of 52% in the total number of TH-IR neurons in the group aged 65-89 years compared with the group aged 19-64 years. CA1 and CA2 TH-IR neurons were reduced by 44% and 55%, respectively. In young (3 months) and old (2 years) rats, the number of NADPHd+ neurons did not decrease with ageing, but the number of TH-IR neurons was significantly reduced by 21% (P < 0.05). In a companion study on monkey retina, we have shown that a postmortem delay of 12.5 hours between death and fixation results in a decrease of 33% in the number of both NADPHd+ and TH-IR neurons in the retina compared with the number in retinas fixed immediately after death. The findings of this study on the two subsets of amacrine cells, therefore, are likely to demonstrate the consequences of ageing in the retina and might contribute to visual impairment in the elderly.