Gene expression of catecholamine biosynthetic enzymes following exercise: modulation by age

Both age and exercise training are associated with tissue specific alterations in the catecholaminergic system. We examined the effect of short-term exercise training on tyrosine hydroxylase and dopamine beta-hydroxylase gene expression in adrenals and specific brain regions with aging. In addition, we examined activator protein-1 and cyclic AMP response element transcription factor binding activity in the adrenal medulla. Male, six- and 24-month-old F-344 rats were exercised by treadmill running for five consecutive days. One group was killed immediately and a second group was killed 2h after the last training session. Exercise significantly elevated tyrosine hydroxylase messenger RNA equally in adrenals of both young and old rats. Training had no effect on dopamine beta-hydroxylase messenger RNA in adrenals of young, but levels were elevated in old rats. Binding activities of both activator protein-1 and cyclic AMP response element binding protein were diminished with age in the adrenal medulla. Exercise training had no significant effect on the binding activity of cyclic AMP response element binding protein in either young or old animals, whereas activator protein-1 binding activity increased equally in young and old animals. Exercise training revealed divergent changes in tyrosine hydroxylase messenger RNA in brain catecholaminergic neurons. In the locus coeruleus and the ventral tegmental areas, training elevated tyrosine hydroxylase messenger RNA levels only in young rats. In the substantia nigra, there was no change in young, but a 45% increase in tyrosine hydroxylase messenger RNA in old rats. In the ventral tegmental area, training increased tyrosine hydroxylase gene expression 80% in young but not in old rats. These results indicate that short-term exercise training increases tyrosine hydroxylase messenger RNA levels in young animals in the adrenals, the locus coeruleus and the ventral tegmental area. The responses for exercise training of aged animals differed from the young in brain noradrenergic and dopaminergic nuclei, especially in the substantia nigra, and to some extent in the locus coeruleus and the ventral tegmental area.