Acetylcarnitine modulation of the morphology of rat hippocampal synapses

OBJECTIVE: To measure the effect of chronic administration of acetylcarnitine (ALCAR) on the morphologic plasticity of rat hippocampal synapses. STUDY DESIGN: Computer-assisted morphometry was carried out on the ultrastructure of hippocampal synapses in 6-, 12- and 22-month-old rats and in age-matched animals chronically treated with ALCAR from the age of 1 month up to when they were killed. Synaptic numeric (Nv) and surface (Sv) densities as well as the synaptic average area (S) were measured in the dentate gyrus supragranular layer. RESULTS: In control animals, Nv was constant between 6 and 12 months of age but significantly decreased in 22-month-old rats, S did not show significant differences due to age and Sv was unchanged between 6 and 12 months but decreased significantly in the old animals. In ALCAR-treated rats, Nv increased and S decreased significantly vs. age-matched controls. Sv showed lifespan constancy among the age groups analyzed. In ALCAR-treated rats the number of synapses smaller than 0.08 microns 2 increased by 18%, 9% and 10% at 6, 12 and 22 months of age, respectively. CONCLUSION: We interpret these findings to represent positive modulation of the synaptic structural dynamics in ALCAR-treated animals through improvements in energy provision at nerve terminals.