In individual rats, em N /em -acetylcysteine also prevented the capacity of cocaine to produce a long-term reduction in extrasynaptic basal glutamate in the nucleus accumbens

In individual rats, em N /em -acetylcysteine also prevented the capacity of cocaine to produce a long-term reduction in extrasynaptic basal glutamate in the nucleus accumbens. HCl (100 mg/kg, i.p.; Fort Dodge Animal Health, Fort Dodge, IA) and xylazine (2 mg/kg, i.p.; Lloyd Laboratories, Shenandoah, IA) anesthesia. A silicon tubing catheter (Dow Corning, Midland, MI; 0.64 mm inner diameter; 1.19 mm outer diameter) was implanted such that it joined the jugular vein through the right posterior facial vein and terminated at the right atrium. The catheter was sutured to the vein at the entry point. The distal aspect of the catheter, which consisted of a 22-gauge guide cannula (Plastics One, Roanoke, VA) attached with dental acrylic to a piece of polypropylene monofilament surgical mesh (Atrium Medical, Hudson, NH), exited 2 cm posterior to the scapulae. Throughout the experiment, catheters were filled daily with a KPT276 heparin solution (83 i.u./ml; Elkins-Sinn, Cherry Hill, NJ) and capped when disconnected from the leash/delivery line assembly. Rats included in microdialysis studies were also implanted with indwelling bilateral guide cannulas (20 gauge, 14 mm; KPT276 Plastics One) using the following coordinates derived from Paxinos and Watson (1986): +0.9 mm anterior, 2.5 mm mediolateral to bregma, and ?4.4 mm from the surface of the skull at a 6 angle from vertical. The placement of the active region of the microdialysis probe, which began 2 mm beyond the ventral tip of the guide cannulas, was primarily in the nucleus accumbens core, although regions immediately dorsal and ventral to this were also likely Rabbit Polyclonal to SREBP-1 (phospho-Ser439) sampled. After surgery, rats were given at least 5 d to recover before testing. During this time, rats were provided acetaminophen (480 mg/L) in their drinking water and injected daily with a sterile cefazolin antibiotic solution (15 mg, i.v.; West-Ward Pharmaceutical, Eatontown, NJ). Self-administration training Self-administration occurred in operant chambers (ENV-008CT; MED-Associates, St. Albans, VT) housed in sound-attenuating cubicles (ENV-016M; MED-Associates) and equipped with two retractable levers, two stimulus lights, and a water bottle. At least 5 d after surgery, rats were food restricted for 18 h with water available = 19), = 10), salineCcocaine (= 18), and = 12). Escalation was evident as a statistically significant increase in the number of infusions obtained relative to the KPT276 first 6 h session. Experiment 2: impact of = 11), = 11), salineCcocaine (= 13), and = 15). Rats then remained in the home cage for a 21 d drug-free period (day 28 of the experiment), and were then challenged with saline or cocaine (15 mg/kg, i.p.) in the absence of = 14, = 6), salineCcocaine (= 14), and = 7). After self-administration, rats underwent extinction training and a subsequent microdialysis/reinstatement test day as described below. Extinction training. After completing 10 maintenance self-administration sessions, rats remained in their home cages for 7 d before extinction training. A 7 d delay was used to ensure an adequate drug-free period before reinstatement, even in rats that quickly extinguished responding. Extinction training involved placing rats into the operant chambers for 2 h/d as described above in the self-administration section except each active lever press now resulted in an infusion of saline. This continued until the mean number of lever presses was 15 responses across at least three sessions, at which point rats were tested for drug-primed reinstatement. Because the average number of extinction sessions needed to meet criteria (SEM) was 11.7 1.10, reinstatement testing occurred 18 d after the last self-administration session. microdialysis and reinstatement test day. On the night before the reinstatement test, microdialysis probes, constructed as previously described (Baker et al., 2003), were inserted into indwelling guide cannula. Rats were then housed overnight in the self-administration chambers. The next day, dialysis buffer (5 mm glucose, 140 mm NaCl, 1.4 mm CaCl2, 1.2 mm MgCl2, and 0.15% PBS, pH 7.4) was pumped through the probes at a rate of 2 l/min for at least 3 h to permit an adequate period of time for glutamate levels to stabilize. After this, basal glutamate levels were sampled over 60 min. Rats were then injected with cocaine (10 mg/kg, i.p.) and the levers were extended. Extracellular glutamate and operant responding were assessed over the next 120 min (= 6C14/group). Quantification of glutamate. The concentration of glutamate in dialysis samples was quantified by comparing peak heights from samples and external standards using HPLC coupled to fluorescence detection. Precolumn KPT276 derivatization of glutamate with opthaldehyde was performed using a Shimadzu LC10AD VP autosampler. The mobile phase consisted of 13% acetonitrile, 100 mm Na2HPO4, and 0.1 mm EDTA, pH 5.90. Glutamate was separated using a reversed-phase column (4 m; 140 6.0 mm; Phenomenex, Torrance, CA), and detected using a Shimadzu 10RF-AXL fluorescence detector with excitation and emission wavelengths of 320 and 400 nm, respectively. Histology. Rats included in the microdialysis studies were given an overdose of pentobarbital (60 mg/kg, i.p.),.