Neurochemical parameters of the main neurotransmission systems in aging mice

The present work was designed to study the effect of aging on some parameters of the glutamatergic, aminergic and cholinergic neurotransmission, in the main brain areas of mice of the long-surviving BALB/c-nu strain. We have assayed: (1) the density of three ionotropic receptors for excitatory aminoacids (EAA) which selectively bind kainic acid (KA), N-methyl-d-aspartate (NMDA) and 2-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA); (2) the content of dopamine (DA), norepinephrine (NE) and serotonin (5-HT) and the levels of the DA metabolite dihydrophenylacetic acid (DOPAC) and the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA); (3) the level of the choline acetyltransferase (ChAT), the enzyme catalyzing the synthesis of acetylcholine. The parameters were measured in animals at the age of 6, 12, 18 and 24 months; the brain zones under test were the frontal cortex (FC), the corpus striatum (STR), the hippocampus (HIP), the medio-dorsal cortex (DC) and the cerebellum (CER). Significant age-related variations for the density of KA-type and NMDA-type receptors were found in STR and a decrease of the NMDA parameter was found in DC. Neither the monoamine and metabolite contents nor the ChAT levels showed any significant variation in all the tested areas. These findings suggest that an unbalance among different neurotransmission activities could take place with normal aging in rodents: it could be involved in the onset of the motor deficit which occurs in the elderly of these and other mammals.