Unbiased estimation of neuronal numbers in the human nucleus coeruleus during aging.

The total number of the neuromelanin-containing neurons of the nucleus coeruleus was determined by means of a newly developed unbiased stereological counting scheme and a low-cost apparative set-up. The individuals (n = 20, age from 49-98 years) included in this study were carefully examined for absence of neurological or psychiatric disorders. However, minor Alzheimer's disease-related neurofibrillary changes occurred in some of the individuals of higher age and these changes were staged. The mean number of neurons per side of the nucleus coeruleus was 15,731 +/- 3,408 SD with a range from 11,737 to 25,319. In three individuals, we compared the left and right nuclei and did not observe significant side differences between the numbers of neurons. There was no correlation between the age of the individuals and the cell number. Also, no correlation was detected between the cell number and the staged occurrence of minor neurofibrillary changes of the Alzheimer type. Due to the novel counting method, the determination of the total cell number took less than 2 h per case.