Intraischemic Nitrous Oxide Alters Neither Neurologic Nor Histologic Outcome: A Comparison with Dizocilpine

Abstract

N-Methyl-D-aspartate receptor antagonism contributes to the anesthetic action of nitrous oxide (N(2)O). We examined the effects of the N-methyl-D-aspartate antagonists N(2)O and dizocilpine on outcome from filament occlusion of the middle cerebral artery (MCAO). Rats breathed 70% nitrogen/30% oxygen or 70% N(2)O/30% oxygen during MCAO. A third group breathed 70% nitrogen/30% oxygen and was given dizocilpine (0.25 mg/kg IV). After 75 min of MCAO, the rats recovered for 3 or 14 days. Pericranial temperature was maintained at 37.5 degrees C +/- 0.2 degrees C during ischemia and for 20 h postischemia. N(2)O did not alter neurologic scores at 3 days (N(2)O, 21 +/- 6; nitrogen, 22 +/- 8; P = 0.95; 0 = normal; 48 = maximal deficit; mean +/- sd; n = 15) or 14 days (N(2)O, 13 +/- 6; nitrogen, 12 +/- 6; P = 0.93; n = 15-16) postischemia. N(2)O had no effect on infarct size at 3 days (N(2)O, 162 +/- 45 mm(3); nitrogen, 162 +/- 61 mm(3); P > 0.99) or 14 days (N(2)O, 147 +/- 56 mm(3); nitrogen, 151 +/- 62 mm(3); P = 0.99) postischemia. Dizocilpine treatment caused smaller infarcts (3 days: 66 +/- 49 mm(3), P < 0.0001 versus nitrogen; 14 days: 84 +/- 50 mm(3), P < 0.006 versus nitrogen) and reduced the neurologic deficit (3 days: 10 +/- 10, P = 0.002 versus nitrogen; 14 days: 6 +/- 7, P = 0.006 versus nitrogen). N(2)O (70%) had no effect on either behavioral or histologic outcome from transient focal cerebral ischemia when compared with results in rats breathing 70% nitrogen. These results indicate that normobaric N(2)O does not alter the response of rat brain to a focal ischemic insult.

Video training and certification program improves reliability of postischemic neurologic deficit measurement in the rat

“…Other untested systems (e.g. Supplemental Table 4) may be as good or better than that of Yokoo et al 14 Further, inspection of neurologic score data for animals with large infarcts (e.g. >250 mm…”

“…SD: standard deviation. *P < 0.0001, paired t-test the Yokoo et al system 14 had the highest point estimate for the correlation with infarct size and was therefore selected for use in our video training program.…”

“…In conclusion, a VTCP program was developed and shown to improve inter-rater agreement in assessing neurologic function in rats subjected to MCAO when using two different scoring systems (Garcia et al 13 and Yokoo et al 14 ). Based on these findings, a VTCP program is likely to be valuable within laboratories and in multi-institutional preclinical trials of stroke therapeutics by improving inter-rater reliability and potentially decreasing the number of animals required for robust efficacy analysis.…”

“…13 The Yokoo system incorporates elements of both the Bederson and Garcia systems but offers a more diverse scoring range (0-48 total points) derived from 14 categories. 14 Fourteen days post-MCAO, three independent expert raters, each having >four years experience scoring post-MCAO neurologic function using all elements of the three systems, simultaneously scored neurologic function in the 16 rats using the three systems while observing each rat being handled by a fourth expert rater. All expert raters were masked to ischemia durations and did not confer with the other expert raters during the scoring process.…”

“…A video segment was collected reflecting all 14 scoring categories in each rat. The trainee raters were provided with copies of the published scoring criteria 14 and a score sheet for each rat (Supplemental Figure 1). Upon completion of the Certification Video, a single investigator (HT) checked the newly trained raters' scores.…”