Age-associated changes in the number of neurons in the right atrium

1. It has been demonstrated that chronotropic responses differ in healthy elderly subjects compared to those in younger normal adults. To evaluate the involvement of the autonomic nervous system, we determined the number of neurons in right atrial strips from six elderly individuals (aged 77 +/- 3.4 years) five of whom had died as the result of extracardiac causes, and from younger adult controls (aged 44.0 +/- 6.0 years) who had died in traffic accidents. 2. There was a significant reduction in the number of neurons of the group of hearts from the elderly (3587 +/- 445, mean +/- SEM) compared with the control group (6412 +/- 377) of five hearts from younger adults (P less than 0.001). 3. It is suggested that this decrease in the number of neurons contributes to the reduced chronotropic responses in the aged. The mechanisms responsible for the neuronal depopulation was not determined.