(A) Light pulse and injection regimen used to determine whether the inhibition of GABAA receptors during various phases between CT 14.5 and CT 21.5 would inhibit light-induced phase delays. All groups received a light pulse (15 min, 150 lux) at CT13.5 followed by 8 hourly intracranial injections containing either vehicle or bicuculline (0.9mM) into the SCN region between CT14.5 and CT21.5. Animals received one of 6 injection regimens (VEH = vehicle; BIC = bicuculline) (N’s: A=19, B=7, C=6, D=10, F=17. (B) Mean±SE of phase delays produced by the various injection regimens outlined in A.