Manually segmented hippocampal ROIs were used to conduct small volume correction in statistical analyses. Statistical analysis was performed in a factorial framework implemented in SPM5, with treatment group as the between subject factor and time as within subject factor. Small-volume correction was applied using the hippocampal ROI generated above. Family-wise error (FEW) multiple-comparison selleck chemical correction was applied to all statistical tests with a corrected height threshold of p = 0.05. Surface renderings of whole-brain and hippocampus ROIs
were generated in 3D Slicer (www.slicer.org) using a volume ray casting rendering equation. Maximum intensity projections of T- and F- statistic find protocol maps were rendered and overlaid onto the ROI isosurfaces using the volume render module in 3D Slicer. The glutamate biosensor (model 7004, Pinnacle Technologies) was established to be sensitive to micromolar concentrations of glutamate, able to detect rapid changes in extracellular glutamate efflux (<0.5 s response), selective for glutamate, and sufficiently small
(130 μM dimension sensing probe) to selectively measure changes within hippocampal subregions (see Hu et al., 1994). On the morning of the experiment, glutamate biosensors were calibrated against glutamic acid using a three-step concentration curve applied over 3 min. The selectivity of the biosensor response was then tested by administration of 125 mM aminophylline of ascorbic acid and tracing observed over an additional 3 min. After precalibration, the biosensors were rinsed in ultra-pure H2O and then immediately implanted via the arm of the stereotax for in vivo recording. Sensitivity of the biosensor response (at least 3 nA per 10 μM glutamic acid), stability of the response, as well as a nonresponse to ascorbic acid were required for the biosensor to be inserted for in vivo experiments. Mice were anesthetized with chloral hydrate (400 mg/kg) and placed in a stereotax with heating pad postinduction,
at which time a 0.6 mm i.p. catheter for drug delivery was inserted. Calibrated biosensors were then directly inserted into the ventral hippocampus and connected to the potentiostat for in vivo recording. Following baseline stabilization of extracellular glutamate signal over one hour, ketamine 30mg/kg or saline was administered via the i.p. catheter and extracellular glutamate response recorded from each hippocampal subregion location over the following 30 min (Bregma coordinates EC A-P 4.7, M-L 3.0, D-V 4.0; dentate gyrus A-P 3.4, M-L 2.7, D-V 3.8; CA1 subfield A-P 3.5, M-L 3.25, D-V 4.2; subiculum A-P 3.9, M-L 3.25, D-V 4.2.) Postexperiment, animals were removed from the stereotax, overdosed with chloral hydrate and euthanized by cervical dislocation.