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

Age-related spatial reference and working memory deficits assessed in the water maze

Aged rats have spatial memory deficits relative to young rats. The extent of these deficits in intermediate-aged rats is not well established. The present study examined the pattern of age-related changes in spatial reference and working memory in four ages of Fischer-344 rats. Place discrimination (PD) in the Morris water maze measured spatial reference memory. Repeated acquisition (RA), a discrimination in which the escape platform location varied from session to session, measured spatial working memory. Fischer-344 rats, 4 months, 11 months, 17 months, and 24 months of age, were tested. Compared to 4-month-olds, 24-month-olds were significantly impaired on all six PD measures of performance, 17 months were significantly impaired on five PD measures, and 11 months were significantly impaired on only one PD measure. Only 24-month-olds had a significant working memory impairment in RA relative to 4 months. Reference and working memory measures were distinct as assessed by a principal components analysis. The results indicate a nonlinear age-related spatial memory decline in Fischer-344 rats from 4 to 24 months of age.

Dynamic morphology of the synaptic junctional areas during aging: the effect of chronic acetyl-L-carnitine administration

The ultrastructural features of hippocampal synaptic contact zones have been investigated by means of computer-assisted morphometry in rats of 6, 12 and 22 months of age and in age-matched animals chronically treated with ALCAR at a daily dose of 50 mg/100 g body weight from the age of 1 month up to the day of sacrifice. The number of synapses/microns 3 (Nv), the average size of the junctional areas (S) and the total area of the synaptic contact zones/microns 3 (Sv) were measured in tissue samples stained by means of the ethanol phosphotungstic acid (E-PTA) preferential technique for synaptic membranes. 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; Sv was unchanged between 6 and 12 months, but it decreased significantly in the old animals. In ALCAR treated rats Nv increased and S decreased significantly vs. Age-matched controls. Sv showed a lifespan constancy among the groups of age analysed. In ALCAR treated rats the number of contact areas smaller than 0.08 micron 2 increased by 18, 9 and 10% at 6, 12 and 22 months of age, respectively. ALCAR administration resulted in a lifespan modulation of synaptic structural dynamics. A proper metabolism at nerve terminals is accounted to play a crucial role in synaptic remodelling potential: on the basis of current research data, it is suggested that ALCAR may improve neuronal bioenergetic mechanisms.

Membrane arachidonic acid concentration correlates with age and induction of long-term potentiation in the dentate gyrus in the rat

We examined the induction and maintenance of long-term potentiation (LTP) in vivo in the dentate gyrus of 4-month-old and 22-month-old urethane-anaesthetized rats. High-frequency stimulation of the perforant path induced an immediate increase in the slope of the population excitatory postsynaptic potential (EPSP), which was sustained in the 4-month-old animals for the duration of the experiment (45 min post-tetanus). In the 22-month-old group, the mean slope of the population EPSP decreased almost to baseline by the end of the experiment. Examination of the individual records indicated that LTP was sustained for the duration of the experiment in half of the 22-month-old animals, while in the others only post-tetanic potentiation was observed. Membrane arachidonic acid concentration was reduced in aged compared with young animals and was lowest in the subgroup of aged animals which failed to sustain LTP. Potassium-stimulated, calcium-dependent release of glutamate was also decreased in aged compared with young animals, but LTP was associated with an increase in glutamate release in the 4-month-old group and 22-month-old subgroup in which LTP was successfully sustained; no change was observed in the 22-month-old group in which LTP was not sustained. The results indicate a correlation between membrane arachidonic acid concentration, glutamate release and ability to sustain LTP in aged animals.

The function of the NMDA-receptor during normal brain aging

Age-related changes of N-methyl-D-aspartate (NMDA) receptors have been found in cortical areas and in the hippocampus of many species. On the basis of a variety of experimental observations it has been suggested that the decrease of NMDA-receptor density might be one of the causative factors of the cognitive decline with aging. Based on these findings several strategies have been developed to improve cognition by compensating the NMDA-receptor deficits in aging. The most promising approaches are the indirect activation of glutamatergic neurotransmission by agonists of the glycine site or the restoration of the age-related deficit of receptor density by several nootropics.

Glutamatergic treatment strategies for age-related memory disorders

Age-related changes of N-methyl-D-aspartate (NMDA) receptors have been found in cortical areas and in the hippocampus of many species. On the basis of a variety of experimental observations it has been suggested that the decrease of NMDA receptor density might be one of the causative factors of the cognitive decline with aging. Based on these findings several strategies have been developed to improve cognition by compensating the NMDA receptor deficits in aging. The most promising approaches are the indirect activation of glutamatergic neurotransmission by agonists of the glycine site or the restoration of the age-related deficit of receptor density by several nootropics.