Cerebral cortical aquaporin-4 expression in brain edema following cardiac arrest in rats.
OBJECTIVE
Brain edema occurs following clinical as well as experimental cardiac arrest (CA) and predicts a poor neurologic outcome. The objective of this study was to determine the expression of cerebral cortex aquaporin (AQP)-4, a member of a family of membrane water-channel proteins, in brain edema formation following normothermic or hypothermic CA.


METHODS
Twenty-four rats were subjected to time-matched normothermic (N-Sham, 37.5 degrees C +/- 0.5 degrees C, n = 6) or hypothermic (H-Sham, 34 degrees C +/- 0.5 degrees C, n = 6) sham experiments and normothermic (N-CA, n = 6) or hypothermic (H-CA, n = 6) CA induced by asphyxiation for 8 minutes. Hypothermia was induced before CA. The animals were resuscitated with cardiopulmonary resuscitation, ventilation, and epinephrine administration. Brain edema was determined by brain wet-to-dry weight ratio at one hour of resuscitation. AQP4 immunoactivity in the cerebral cortex was determined using immunohistochemical staining and was semiquantified as an intensity of staining with an automated cell imaging system.


RESULTS
Mild hypothermia in the sham experiments did not alter cerebral cortex AQP4 immunoactivity (mean +/- SD) (55.0 +/- 3.7 in H-Sham vs. 53.3 +/- 1.7 in N-Sham, p > 0.05). N-CA resulted in a significant increase in AQP4 immunoactivity (61.8 +/- 4.5) compared with N-Sham (p = 0.01) and H-Sham (p = 0.03). H-CA attenuated AQP4 compared with N-CA (53.4 +/- 1.3, p = 0.01). Brain wet-to-dry weight ratios were 4.41 +/- 0.07 in N-Sham, 4.40 +/- 0.08 in H-Sham (p > 0.05 vs. N-Sham), 4.55 +/- 0.04 in N-CA (p = 0.004 vs. N-Sham; p = 0.005 vs. H-Sham), and 4.43 +/- 0.09 in H-CA (p = 0.02 vs. N-CA; p > 0.05 vs. N-Sham and H-Sham).


CONCLUSIONS
Cerebral cortical AQP4 expression is up-regulated after normothermic CA, which is attenuated by hypothermia induced before CA.
Department of Emergency Medicine, Louisiana State University Health Sciences Center, 1501 Kings Highway, Shreveport, LA 71130, USA. fxiao@lsuhsc.edu.
Feng
F
Xiao
Thomas C
TC
Arnold
Shu
S
Zhang
Carlos
C
Brown
J Steven
JS
Alexander
Donna L
DL
Carden
Steven A
SA
Conrad
D000818:Animals; D051401:Aquaporin 4; D020346:Aquaporins / Q000378:metabolism*; D001794:Blood Pressure; D001929:Brain Edema / Q000209:etiology* / Q000378:metabolism* / Q000473:pathology; D002540:Cerebral Cortex / Q000378:metabolism*; D004195:Disease Models, Animal; D006323:Heart Arrest / Q000150:complications*; D007036:Hypothermia, Induced; D009929:Organ Size; D051381:Rats
C496032:Aqp4 protein, rat; D051401:Aquaporin 4; D020346:Aquaporins