iDREADDs activation
Each behavioural condition was run both after an infusion of clozapine
and after an infusion of saline, which served as a within-subject
control. Clozapine was infused on two separate occasions per condition,
reflecting the potential for greater within-subject variability. The
infusion order was counterbalanced between the two cohorts (Figure 1).
There was always an added infusion-free test day between the two
clozapine infusions for Conditions 1-4, i.e., apart from the Dark
condition.
Animals were first habituated to the infusion procedure, using saline,
prior to the commencement of behavioural testing with clozapine. On
infusion days, the animals were taken to a separate room in pairs and
lightly anaesthetized with an isoflurane-oxygen mixture (5% induction,
1.5-2% maintenance). Double infusion injectors (33-gauge, PlasticsOne,
Virginia, USA) were inserted into the guide cannula and either 1µl of
sterile saline or 1µl of clozapine (1mg/ml) was infused over 1 minute
using an infusion pump (11 Plus, Harvard Apparatus, UK). The injector
was held in place for a further minute and the dummy cannula replaced.
The infusions lasted no more than 4 minutes per animal, and the animal
was returned to its home cage. Animals rested for 15-20 minutes prior to
behavioural testing.