Endogenous GABA concentration in cortical synaptosomes from young and aged rats

Abstract

The objective of this study are threefold: (1) to compare the γ-aminobutyric acid (GABA) concentration of a preparation of cortical snaptosomes from young male rats to that of aged rats; (2) to compare the GABA concentration in synaptosomes retained by Millipore filtration for young and aged rats; and (3) to compare the GABA concentration in the synaptosomal preparation to that in synaptosomes retained by Millipore filtration for young and aged rats. The GABA concentration is measured in cortical synaptosomes from Long-Evans rats at 2 months and 30 months of age. Concentration of the synaptosomal preparation declined significantly from 2.97 mM in 2-month animals to 2.68 mM in 30-month animals. In order to compare the results with previous studies of GABA transport, in which Millipore filters are used to separate synaptosomes from incubation medium, the GABA concentration is also measured following placement of synaptosomes on 0.65μ pore size Millipore filters. For both young and aged animals, this population of synaptosomes is found to contain GABA at a concentration more than triple that in the overall population. This is the expected result if the filtration process reduce the non-synaptosomal component of the total preparation, since GABA uptake is known to be a function of the nerve-ending component. Comparison of 2-month and 30-month synaptosomes reveals that the GABA concentration of those synaptosomes retained by the filtration process declined to a greater extent in the aged group than did the content of the overall population (from 9.33mM to 8.37mM). The results are consistent with previous studies of the aging of the GABA transporter in this preparation, in which it was found that the GABA transport capacity declined in the 30-month age group.