Unbiased morphometrical measurements show loss of pigmented nigral neurones with ageing

This study used the dissector method to evaluate pigmented nigral neuronal loss in the substantia nigra pars compacta with age. Dissector counts can be used to estimate the absolute and accurate total neurone numbers. In addition, the area and diameter of the neuronal cell body was estimated by using a computerized morphometric analysis in a single section of the substantia nigra pars compacta. Brain samples from 26 people with an age range from 17 to 90 years were studied. A significant decrease in the total number of pigmented neurones (r=-0.83, P<0.001) and their density (r=-0.83, P<0.001) with age was found in the substantia nigra pars compacta. The number of pigmented neurones counted from a single section also showed an age-dependent decline (r=-0.76, P<0.001). According to the regression equations, the total number of pigmented neurones estimated by dissector counts decreased by 9.8% per decade and the neuronal density decreased by 7.4% per decade. The area of the neuronal cell body decreased by 3.2% per decade. This latter change corresponds to an approximate 4.4% decrease per decade in neuronal volume. These findings show that both the number of pigmented neurones and their size in the substantia nigra pars compacta decreases with age. However, the reductions in the total number of pigmented neurones are more dramatic than the reduction in neurone size with ageing.