Surgical implantation of guide tubes for microdialysis.

Humane procedures for implantation of intracranial guide tubes, placement of microdialysis probes, and in vivo microdialysis (Coleman et al. 2006; Van Dort et al. 2009; Wathen et al. 2012) have been described in detail and are outlined below. All anesthetic inductions used loss of righting response as a surrogate measure for loss of consciousness (Vanini et al. 2014). Mice were placed in an induction chamber, and isoflurane (2.5%) was delivered in 100% oxygen at a flow rate of 1 L/min. When the mouse stopped moving, the chamber was gently tipped to turn the mouse on its side and to determine whether the mouse would right itself. When the mouse did not right itself, the mouse was removed from the induction chamber and isoflurane was delivered using a nose cone while the mouse was shaved and scrubbed for surgery. Antinociception was assessed using paw withdrawal in response to pinch of a hindlimb footpad. The mouse was then moved to a stereotaxic frame (David Kopf Instruments; model 962) equipped with a mouse adaptor (model 962) and a mouse anesthesia mask (model 907). Delivered isoflurane concentration was reduced to 1.5% at a flow rate of 0.6 L/min and was measured continuously by spectrophotometry (Cardiocap/5; Datex-Ohmeda). During surgical implantation of a microdialysis guide cannula (CMA 7), core body temperature was held at 36–37°C by use of a circulating hot water pump (TP400 T/Pump heat therapy system; Gaymar) connected to a water-filled heating pad. Delivered isoflurane concentration, core body temperature, and breathing rate were recorded every 10 min. A CMA 7 guide cannula was implanted 1 mm above the targeted dialysis site, which was 3 mm anterior, 1.6 mm lateral, and 2 mm ventral to bregma (Paxinos and Franklin 2018). At the conclusion of the guide cannula implantation surgery, isoflurane delivery was terminated and the mouse was placed on its back in a heated recovery chamber. When the mouse righted itself, it was again placed on its back and a second successful righting response was confirmed. When the mouse ambulated normally, it was returned to its home cage. Mice were given at least 1 wk of recovery from the guide tube implantation surgery before they were used for a microdialysis experiment.