Effect of acetyl-L-carnitine on the dopaminergic system in aging brain.

We studied the effect of acetyl-L-carnitine (ALCAR) on dopamine release and the effect of long-term acetyl-L-carnitine treatment on age-related changes in striatal dopamine receptors and brain amino acid levels. In striatal tissue that had been incubated with [3H]dopamine, acetyl-L-carnitine increased the release of [3H]dopamine evoked by electrical stimulation. In striatal tissue from aged mice administered acetyl-L-carnitine for 3 months, the release of [3H]dopamine evoked by electrical stimulation was higher than that of its aged control; the release after a second stimulation was similar in the two groups. There was a significant decline in the number of D1 striatal dopamine receptors with age. The Bmax was 51% lower in 1.5-year-old mice than in 4-month-old animals. Administration of acetyl-L-carnitine for 3 months diminished the reduction in the binding of [3H]SCH-23390. [3H]Spiperone binding to D2 receptors was not decreased with age and was not affected by acetyl-L-carnitine treatment. Age-related decreases in levels of several amino acids were observed in several brain regions. Acetyl-L-carnitine lessened the reduction in the level of taurine only in the striatum. The findings confirm the multiple effects of acetyl-L-carnitine in brain, and suggest that its administration can have a positive effect on age-related changes in the dopaminergic system.