Region-specific alterations of neuronal nitric oxide synthase (nNOS) expression in the amygdala of the aged rats

Although many amygdalar functions are altered by aging, little is known about their mechanisms. As these functions are related with nitric oxide (NO), we examined neuronal nitric oxide synthase (nNOS) expression in the amygdala of the aged rats via immunohistochemical technique. We found that nNOS immunoreactive neurons are decreased in almost all amygdalar areas of the aged rats, while nNOS immunoreactivity of the neuropil is significantly increased in the amygdalar nuclei related with main and accessory olfactory system. These suggest altered levels of NO might provide region-specific mechanisms of many physiological and behavioral deficits of the amygdala developed by aging. However, exact effects of these changes require further elucidation.