Circadian activity of the GABAergic system in the golden hamster retina

Daily changes in gamma -aminobutyric acid (GABA) turnover rate were studied in the golden hamster retina. This parameter showed significant variations throughout the light-dark cycle, with minimal values during the day. Retin al glutamic acid decarboxylase (GAD) activity was higher at midnight than a t noon. Moreover, [[H-3]GABA binding significantly varied throughout the 24 -h cycle, with maximal values during the day. Saturation studies performed at 12:00 and 24:00 h indicated that the maximal concentration of [H-3]GABA binding sites (B-max) was significantly higher at noon, whereas the dissoci ation constant (K-d) remained unchanged. High K+-induced GABA release was s ignificantly higher at midnight than at midday. Daily variations in retinal GABA turnover rate, GABA release, and in its specific binding persisted in golden hamsters exposed to constant darkness. In summary, these results su pport the idea of a circadian clock-controlled GABAergic activity in the ha mster retina. (C) 2001 Elsevier Science B.V. All rights reserved.