Glutamate-glutamine cycle and aging in striatum of the awake rat: Effects of a glutamate transporter blocker

This study investigated the effects of aging on the actions of a specific g lutamate reuptake blocker, L-trans-pyrrolidine-2, 4-dicarboxylic acid (PDC) , in extracellular glutamate and glutamine in striatum of the awake rat. Mi crodialysis experiments were performed on young (2-3 months), middle-aged ( 12-14 months), aged (27-32 months) and very aged (37 months) male Wistar ra ts. Local infusion of PDC (1-4 mM) in striatum increased the dialysate conc entration of glutamate and decreased dialysate concentration of glutamine i n all the age-groups. In young rats, decreases of dialysate glutamine were correlated with increases of dialysate glutamate. The same profile glutamin e/glutamate as in young rats was found in middle-aged, aged and very aged r ats, which suggests that the action of glutamate on the glutamate-glutamine cycle in striatum of the awake rat is not modified as a consequence of agi ng. We also found a significant correlation between the increases of glutam ate produced by PDC and the basal dialysate concentration of glutamine, a r elationship that did show a significant change with age. Although the signi ficance of this latter finding remains to be elucidated, it may be importan t to understand the changes in glutamate-glutamine cycle during aging.