Figure 1.

Extrasynaptic GABA_ARs contribute to the acute effects of GABA in the SCN during the subjective night but not during the subjective day. The nonselective GABA_A-PHASIC/GABA_A-TONIC agonist muscimol (2.2 nmol) phase advanced the pacemaker at CT6, whereas the GABA_A-TONIC receptor superagonist THIP (22 nmol) had no effect (A). Both agonists were effective in blocking the phase shifting effects of a 15-min 150 lux light pulse during the subjective night (CT13.5 and CT19; B, C, respectively). THIP was more effective than muscimol at blocking photic phase delays at CT13.5 (B). In the absence of a light pulse, animals treated with THIP showed a small phase delay compared with those treated with muscimol at CT13.5 (B). Neither muscimol nor THIP had an effect on phase in the absence of a light pulse during the late subjective night (C). NP, no light pulse; LP, light pulse (150 lux, 15 min), *p ≤ 0.05. Statistics for all analyses in Table 1.