Acetyl-L-carnitine: behavioral, electrophysiological, and neurochemical effects.

Aged rats were chronically administered acetyl-L-carnitine (AC) for 10 months. During this period they were tested on learning and sensorimotor tasks and were then subsequently tested electrophysiologically to assess induction and decay rates of long-term synaptic enhancement (LTE) in the hippocampus. Four groups were tested: young controls (4 mo-con), middle-aged controls (16 mo-con), old controls (24 mo-con), and old AC-treated rats (24 mo-AC). After completion of electrophysiological testing, each rat was sacrificed and investigated for age- or drug-related changes in three neurotransmitter markers; including, NMDA-sensitive glutamate receptors, high affinity choline uptake, and adenosine receptor number in the neocortex, hippocampus or caudate nucleus. Aging impaired spatial learning and there was a robust positive correlation between NMDA receptors in the hippocampus and acquisition of the spatial learning task. Induction of hippocampal LTE was reduced in 24 mo-AC rats and NMDA receptor number and high-affinity choline uptake in the frontal cortex was increased. Several suggestions are offered to explain the action of AC on these neurobiological parameters in old rats.