Abstract
Levels of monoamines and indices of monoaminergic function were evaluated in basal forebrain nuclei [vertical diagonal band nucleus (vDB), horizontal diagonal band nucleus (hDB), nucleus basalis (nbM), medial septal nucleus (mS)] and in other brain areas of female young (3-month-old) and aged (24-month-old) Fischer 344 rats. Concentrations of norepinephrine (NE) decreased 25–60% in the vDB, nbM, mS, and locus coeruleus (LC) of aged rats as compared to young rats. Dopamine (DA) and serotonin (5-HT) levels were unchanged in basal forebrain nuclei of aged rats. Using α-methyl-<i>p</i>-tyrosine, an inhibitor of tyrosine hydroxylase, to evaluate catecholaminergic function showed that NE turnover, an index of NE release over time, decreased 66% in the nbM, 40% in the mS, and 83 % in the LC of aged rats. DA turnover decreased approximately 30% in the vDB, mS, and striatum of aged rats. In contrast, the activity of 5-HT endings, assessed by 5-hydroxyindole-acetic acid (5-HIAA) levels and 5-HIAA/5-HT ratios, increased in the hDB and nbM. These results raise the possibility that age-related decreases in catecholaminergic function within basal forebrain nuclei, which are critical for memory function, may contribute to age-related cognitive impairments.
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