Effects of Progesterone and Other Gonadal Hormones on Glutamatergic Circuits in the Retina

Background: Gonadal hormones function in the retina; however, their targets have not yet been identi-fied. Therefore, the present study examined the effects of progesterone and other gonadal hormones on glutamatergic circuits in the retina. Methods: Extracellular glutamate concentrations, which correspond to the amount of glutamate re-leased, were examined using an enzyme-linked fluorescent assay system. The activity of glutamatergic synapses between bipolar cells and ganglion cells was investigated using a patch clamp technique. Changes in retinal thickness during pregnancy were assessed using optical coherence tomography (OCT) images. Results: Progesterone and pregnenolone sulfate increased extracellular glutamate concentrations, whereas estrogen and testosterone did not. Progesterone increased the activity of glutamatergic synapses between bipolar cells and ganglion cells. A temporal decrease in the thickness of the peripheral retina was observed in the 1^st trimester. Conclusions: Progesterone, but not estrogen or testosterone, activated glutamate release in the mouse retina. Increases in the concentration of progesterone during pregnancy did not induce any detectable change in retinal thickness.