Decline of GABA uptake in the hamster preoptic area following light offset

The uptake of gamma-aminobutyric acid (GABA) was studied in homogenates of the accumbens-preoptic region (APR) of the hamster brain. Aggressive and non-aggressive female hamsters, maintained under a reversed 10-h dark and 14-h light cycle were sacrificed at various times after light offset. Aliquots of the APR homogenates were incubated with a series of [3H]GABA concentrations to obtain values for Vmax and Km. In both groups Vmax values declined sharply after light offset. The reduction in GABA uptake from early to later dark phase parallels the routine diminution in the aggressive activity of rodents from its peak in the early dark phase; the increase in GABAergic inhibition which presumably results from the reduced uptake may contribute to this change in aggressive activity.