In vivo microdialysis

Microdialysis samples were collected and analyzed as previously described (Murnane et al. 2010, 2012). Briefly, all procedures were performed in fully conscious subjects while they sat in a primate chair (Primate Products) within a sound-attenuating testing chamber. After the subject was placed in the chamber, 28mm stainless steel microdialysis probes with 4mm membranes (CMA Microdialysis, Holliston, MA, USA) were inserted into the surgically implanted guide cannulae. For the cocaine studies, three subjects (RDn8, RHp8, RNb7) underwent the microdialysis protocol six times, such that each subject received vehicle and WAY (0.1 and 1.0 mg/kg, i.m.) pretreatments combined with subsequent saline or cocaine (1.0 mg/kg, i.v.) treatments. For the methamphetamine (1.0 mg/kg, i.v.) studies, the same protocol was conducted in four subjects (RDn8, RHp8, RNb7, RJs6). Experiments consisted of a 1h equilibrium period after which samples were collected every 10 min. Vehicle and WAY were administered 30 min after the sampling began and 30 min before saline, cocaine or methamphetamine administration and samples were collected over the next 2h. The viability of the sampling site was verified through retrodialysis of a potassium-enriched (100mm) solution otherwise ionically matched to artificial cerebrospinal fluid (aCSF). Dopamine concentrations within the dialysate were quantified using high-pressure liquid chromatography with electrochemical detection, as previously described (Murnane et al. 2010, 2012). The data were analyzed by comparison with standard concentration curves using Chromeleon 6.8 Chromatography Data System (Thermo Fisher Scientific, Waltham, MA, USA). The doses of cocaine and methamphetamine used in the microdialysis experiments were based on previous studies from our group (Kirkland Henry et al. 2009; Murnane et al. 2013; Berro et al. 2017). In vivo microdialysis sessions were performed no more frequently than every two weeks for each subject. A microdialysis session with either cocaine or methamphetamine following saline pretreatment was conducted between blocks of experiments to rule out the effects of non-specific site damage on the results, and data on different sessions were averaged for each animal. The order of vehicle and WAY doses was randomized and counterbalanced across subjects.