GABA uptake is inhibited by thyroid hormones: implications for depression.

Studies of the effects of thyroid hormones on the uptake of neurotransmitters by homogenates of rat cerebral cortex have revealed a significant competitive inhibition of neuronal uptake of [3H]GABA by thyroid hormones (T3 greater than T4 greater than rT3). The IC50 for inhibition of GABA uptake by T3 was estimated at 4 microM and that of T4 at 11 microns. GABA uptake in homogenates of cerebral cortex from hypothyroid rats was significantly enhanced over that of controls; however, uptake in tissues from hyperthyroid rats was not significantly diminished.