Mini pump

Mice were anesthetized with a mixture of ketamine/xylazine as described in the previous sections and surgically implanted with bilateral NAc guide cannulae (Plastic One). Cannulae (Plastics One) were delivered into the NAc according to bregma coordinates (anteroposterior +1.6 mm, mediolateral +1.5 mm, dorsoventral −4.4 mm) and fixed to the skull with Loctite skull adhesive (Henkel). Saline or a total of 5 ng of IL-6 (diluted at 10 ng/mL in saline solution) was administered over 5 min (0.1 mL /min) using a mini-pump (Harvard Apparatus), followed by a 20-min rest, before subthreshold micro-defeat stress. SI test was conducted 24h later. Mice were then sacrificed and perfused as described above in the IHC section to confirm placement of cannula in the NAc.

Mefloquine hydrochloride, Lot #111M4707V, (Sigma-Aldrich, St. Louis, Missouri) was dissolved in dimethyl sulfoxide (DMSO) for a 38mg/mL stock solution. Intraperitoneal injections (drug: 20 mg/kg mefloquine or 5 mg/kg mefloquine in 0.9% saline, or vehicle: 5% DMSO in 0.9% saline) were administered 20 minutes prior to stress. Direct cannula microinfusions (150 µM mefloquine or 1% DMSO in artificial cerebrospinal fluid; see Electrophysiology methods) were performed using a minipump (Harvard Apparatus, Holliston, Massachusetts) and internal cannula (Plastics One, Roanoke, Virginia) at a rate of 0.1 mL/minute for 5 minutes followed by a 5 minute rest period with the cannula still in place. Drug dosing was based on the doses used for malaria treatment (20 mg/kg) and prophylaxis (5 mg/kg) in humans, as well as previous literature using mefloquine to block gap junctions in mice (12 (link), 13 (link)). Since mefloquine has a long elimination half-life of approximately two to three weeks (14 (link)), the drug was given only once as a pretreatment prior to subthreshold social defeat stress. Subsequent behavioral tests were performed without additional drug administrations.