Stress-induced reinstatement of Fix-C and Esc-C CPP

Stress-induced reinstatement was assessed using the forced swim test (FST). The
FST is a common behavioral paradigm used to model stress-induced relapse to drug use
(Kreibich & Blendy, 2004). Twenty-four hours after a test for CPP extinction, mice were
exposed to FST. Thirty minutes prior to FST mice were injected with either a) MK-801
(0.3mg/kg), b) ifenprodil (10mg/kg), c) 7-NI (25mg/kg), d) antalarmin (10mg/kg) or e)
vehicle. Doses for MK-801, ifenprodil and 7-NI were chosen based on their effectiveness
at disrupting reconsolidation of Fix-C and Esc-C memory (Liddie & Itzhak, 2014,
Chapter 2). A dose of 10mg/kg antalarmin was chosen because this dose was effective at
attenuating swim-induced reinstatement of place preference developed using a fixed dose
schedule of cocaine (McReynolds et al., 2014). For the FST, mice were placed in a
beaker (15cm wide x 19 cm deep) filled to 11cm with water (26±1°C) for 6 min. The
beaker was filled with enough water to avoid tails touching the bottom. After 4min
recovery and drying under a heat lamp in their home cage, CPP was measured for 20min.
Because we found a significant effect of 7-NI on suppressing stress-induced
reinstatement, we also investigated the amount of time mice spent floating/immobile in
each of five separate FST trials during a period of one month following a single
administration of 7-NI or vehicle. Immobility during FST is often interpreted as
depression-like behavior. Thus drugs that reduce immobility during FST are considered
to possess antidepressant properties (Petit-Demouliere et al., 2005).

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