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CO Jaliffa, LD Tesler, MI Keller Sarmient, RE Rosenstein; Circadian Activity of the GABAergic System in the Golden Hamster Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1360.
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Purpose: Dopamine and γ-aminobutyric acid (GABA) are the most studied retinal neurotransmitters regarding responsiveness to light and circadian rhythmicity. In contrast to dopamine, no information is available about time-dependent variations of retinal GABAergic activity. In this context, the aim of the present work was to study the circadian activity of the GABAergic system in the golden hamster retina. Methods: Retinal GABA content and turnover were assessed by a radioreceptor assay, whereas glutamic acid decarboxylase (GAD) activity was determined by the release of 14CO2 from 14C-L-glutamic acid. GABA binding and high K+-induced GABA release were measured using 3H-GABA as a radioligand. These parameters were assessed in the retina of hamsters kept under a light-dark photoperiod as well as in hamsters exposed to constant darkness for 48 h before the experiment. Results: GABA turnover rate showed significant variations throughout the light-dark cycle, with minimal values during the day. Retinal GAD activity was higher at midnight than at noon. Moreover, 3H-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 3H-GABA binding sites (Bmax) was significantly higher at noon. High K+-induced GABA release was significantly 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. Conclusion: In summary, these results support the idea of a circadian clock-controlled GABAergic activity in the hamster retina.
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