Guide cannula

Rats were anesthetized with ketamine (100 mg/kg, i.p.) and xylazine (10 mg/kg, i.p. Sigma Aldrich, USA). First, we implanted a silastic catheter into the external jugular vein, as described by previously (Solecki et al., 2013 ). Second, we implanted an ethylene oxide sterilized polyethylene i.o. catheter that was anchored to the first molar and protruded dorsally through the skin between the ears. For additional, detailed i.o. surgical methodology, see (Wickham et al., 2015 ). Carprofen (5 mg/kg, s.c.) was administered prior to any surgical incision and was administered for three days post-surgery. In preparation for voltammetry experiments, a guide cannula (Bioanalytical Systems, West Lafayette, IL) was positioned above the NAc (AP +1.2 mm, ML −1.4 mm) and an Ag/AgCl reference electrode (previously baked at 120°C for 1 h) was implanted in the contralateral hemisphere (Wickham et al., 2015 ). Subsequently, a bipolar stimulating electrode was implanted in the VTA/substantia nigra (SN) (AP −5.2 mm, ML −0.5 to −1.5 mm, DV −8.0 to −9.0 mm). Dental cement (Dentsply, Milford, DE) and screws (Gexpro, High Point, NC) were used to secure the cannula and reference electrode to the skull.

On the surgery day, rats were anesthetized with isoflurane (induction 5%, maintenance 2%) and placed in a stereotaxic frame on a heated pad. A guide cannula (Bioanalytical Systems, West Lafayette, IN) was implanted above the NAc from bregma: (AP=+1.7 mm; ML=+1.8 mm; DV=−2.5 mm), and an Ag/AgCl reference electrode was implanted in the contralateral cortex. Finally, a bipolar stimulating electrode was implanted above the ventral tegmental area (AP=−5.2 mm; ML=+1.0 mm; DV=−8.6 mm). Animals received ibuprofen (15 mg/kg, PO) immediately after the surgery and once a day for the following two days.

Rats were anaesthetized with ketamine (80 mg/kg, i.p.) and xylazine (20 mg/kg, i.p.) and implanted with a chronic indwelling Silastic^® cannula (0.012 inches inner diameter and 0.025 inches outer diameter) into the right jugular vein (Calipari et al., 2013 (link)). The cannula exited the skin on the dorsal surface in the region of the scapulas. Immediately following catheterization, rats were immobilized in a stereotaxic frame and surgically prepared for freely moving FSCV recording as described previously (Aragona et al., 2008 (link); Sombers et al., 2009 (link)). A guide cannula (Bioanalytical Systems) for housing the microdrive for the carbon-fibre microelectrode was positioned above the NAc shell (+1.7 mm anterior, +0.8 mm lateral, −2.5 mm ventral relative to bregma) (Paxinos & Watson, 1998 ), and a combination bipolar stimulating electrode/guide cannula (26 gauge; Plastics One) was implanted ipsilaterally targeting the VTA (+5.4 mm posterior, +1.2 mm lateral, −7.8 mm ventral) at a 6° angle. An Ag/AgCl reference electrode was placed in the contralateral cortex. All components were permanently affixed with dental cement.

Rats were given a minimum of 2 days habituation to the facility post-transport before surgery. The surgical procedure was performed as described previously ^{53 (link)}, using flat skull stereotaxic coordinates obtained from a brain atlas ⁹⁰ . Briefly, rats were anesthetized with ketamine/xylazine (80–100mg/kg and 2–12mg/kg; i.p., respectively) and placed in a stereotaxic frame (Kopf Instrumentation; Tujunga, CA, USA). Deltaphase isothermal pads (Braintree Scientific, Braintree, MA, USA) were used to maintain body temperature. Bupivicaine was injected just under the skin and the skull was exposed to reveal bregma and lambda in order to level and drill the holes for electrode placement. For the electrochemical experiments, a combination bipolar stimulating electrode/infusion cannula (Plastics One, Roanoke, VA, USA) was placed above the posterior VTA (−5.9 AP, +0.8 ML, −8.8–9.0 DV). A guide cannula (Bioanalytical Systems, West Lafayette, IN, USA) for recording electrodes was positioned 2.5 mm deep into the brain over the shell subregion of the NAc (+1.2 AP, +0.8 ML). Reference electrodes were Ag/AgCl, and placed superficially in the contralateral cortex. For behavioral experiments, stainless steel guide cannulae (26 gauge, Plastics One) were bilaterally aimed at the VTA (−5.9 AP, +1.7 ML, −6.6 DV, relative to bregma) with a 10 degree angle.

Rats were anesthetized with isoflurane (5% induction, 2%
maintenance) and secured in a stereotaxic frame on a heated pad.
Anterior–posterior (AP), medial–lateral (ML), and
dorsal–ventral (DV) positions refer to bregma and coordinates were
obtained from a rat brain atlas (Paxinos and
Watson 1998). A guide cannula (Bioanalytical Systems, West Lafayette,
IN) was implanted above the NAc (AP +1.7 mm, ML +1.7 mm, DV -2.5
mm). An Ag/AgCl reference electrode was implanted in the contralateral cortex. A
bipolar stimulating electrode (Plastics One, Roanoke, VA, polished tips, 1 mm
apart) was implanted in the VTA (AP -5.2 mm, ML +1.4 mm, DV -8.5 mm).
Rats received ibuprofen (15 mg/kg, PO) immediately after surgery and for the
following two days.