Wild-type mice received a series of footshocks (0.5 mA for 2 s, ten times in 5 min; SMSCK, Kinder Scientific) and their activity was video-recorded for 15 min in the footshock chamber, in a novel environment or in the HC immediately after the footshock. For in vivo optogenetics experiments, mice were handled the 4 days preceding behavioural assessment. Blue light was delivered for 5 min (10 Hz, 10 ms pulse width, 15 mW; 473 nm); in LH stimulation experiments, 20 Hz was used. Yellow light (15 mW) was delivered continuously for 15 or 5 min. Behavioural video analysis was conducted by an individual blinded to subject treatment group using a macro in Microsoft Excel. Walking was noted as the animal changed its location or turned as long as the front paws moved. Freezing behaviour was noted if animal showed no movement for at least 3 s, except respiratory movements.
For c-Fos immunolabelling, animals were killed 2 h after light stimulation. For experiments with Arch3.0, after recovery mice were handled for 4 days and HAB to the experimental condition for 3 additional days. After a similar series of footshock, their behaviour was recorded in their HC under continuous yellow light (15 mW) for 15 min. For assessing the involvement of circulating CORT, metyrapone (75 mg per kg, Tocris Bioscience, dissolved in 50 μl polyethylene glycol) was administered i.p. 60 min before footshock. For circulating CORT level measurements, baseline blood samples were taken from the tail vein at least 2 h before light stimulation. Second sampling was done 15 min after the onset of light stimulation. CORT level was measured using an ELISA kit (Arbor Assays). To investigate social cues bedding was not replaced in the HC of mice for 10 days prior testing. Experiment subjects were at the age of 16 weeks while conspecific males were 7 weeks old.
For c-Fos immunolabelling, animals were killed 2 h after light stimulation. For experiments with Arch3.0, after recovery mice were handled for 4 days and HAB to the experimental condition for 3 additional days. After a similar series of footshock, their behaviour was recorded in their HC under continuous yellow light (15 mW) for 15 min. For assessing the involvement of circulating CORT, metyrapone (75 mg per kg, Tocris Bioscience, dissolved in 50 μl polyethylene glycol) was administered i.p. 60 min before footshock. For circulating CORT level measurements, baseline blood samples were taken from the tail vein at least 2 h before light stimulation. Second sampling was done 15 min after the onset of light stimulation. CORT level was measured using an ELISA kit (Arbor Assays). To investigate social cues bedding was not replaced in the HC of mice for 10 days prior testing. Experiment subjects were at the age of 16 weeks while conspecific males were 7 weeks old.
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