Fig. 9. Dependence of glutamate release on light and dark adaptation. (a) Xenopus eyecups were treated to remove neural layers, leaving a layer of intact photoreceptors. These “reduced” retinas were maintained for 5 hours in white light, then dark-adapted for 5 hours. Dark and light periods are indicated by the horizontal bar. Each data point represents the glutamate content of 10-minute samples of superfusate (n = 12, mean ± SE). Data are normalized to the average of the light samples. Glutamate release increased markedly within the first 30 minutes of dark adaptation and slightly within the subsequent 4.5 hours. (b) Reduced retinas were dark-adapted overnight, stimulated by white light for 2 hours, then dark-adapted for 1 hour (n = 7). Data are normalized to the average of the first four dark samples. White light reduced release by about 50%. When the light was extinguished, the release rate increased about twofold. (Schmitz Y, Witkovsky P: Glutamate release by the intact light-responsive photoreceptor layer of the Xenopus retina. J Neurosci Meth 68:55, 1996, with permission of the authors and Elsevier Science B.V.)