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Journal of Biological Rhythms
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Retinal GABAA Receptors Participate in the Regulation of Circadian Responses to Light

Valeria Della Maggiore

Martin R. Ralph

Department of Psychology, University of Toronto, 100 Saint George Street, M5S 3G3, Toronto, Ontario, Canada

A role for retinal [.gamma]-aminobutyric acid Type A (GABAA) receptors in the regulation of circadian responses to light was examined. Intraocular injections of the GABAA antagonist, bicuculline, were performed during the early (Circadian Time [CT] 13.5) and late subjective night (CT 20), followed by a light pulse. Bicuculline significantly decreased the magnitude of phase delays induced by light to 65%, whereas it had no effect on phase advances. To explore the nature of the inhibition elicited by bicuculline, an intensity-response curve was performed. Intraocular injections of bicuculline inhibited phase delays only when induced by high-saturating light illuminances (20 and 100 lux). No effect was observed at light intensities [.lessequal] 5 lux. These results suggest that retinal GABAAreceptors modulate the responsivity of the circadian system to light.

Key Words: GABA • GABAA receptors • circadian rhythms • photoentrainment • retina • bicuculline

Journal of Biological Rhythms, Vol. 14, No. 1, 47-53 (1999)
DOI: 10.1177/074873049901400107
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