title: Effects of repeated brain ischemia induced by rapid lower body negative pressure on brain water and Na+,K+-ATPase activity in rats.
abstract: BACKGROUND
  It has been demonstrated that during +Gz exposure cerebral blood flow is significantly reduced resulting in brain ischemia. Animal centrifuge models are commonly used to investigate the mechanisms of +Gz-induced loss of consciousness (G-LOC) and their pathophysiological effects on the brain. These dynamic models are limited because we currently are unable to obtain accurate measures of membrane ion flux or single cell electrophysiological responses from animals under centrifugation.
  
  
  OBJECTIVE
  The aim of the present study was to develop a non-centrifuge animal model of short-term, repeatable and complete brain ischemia using a rodent lower body negative pressure (LBNP), and to investigate the effects of repeated complete brain ischemia induced by LBNP on brain Na+,K+-ATPase activity, Na+, K+ and water contents in rats.
  
  
  METHODS
  Eight anesthetized rats were exposed randomly to LBNP of -2.67 kPa, -4.00 kPa, and -5.33 kPa, respectively, at the rate of -0.67 kPa x s(-1). The pressure rapidly returned to control level when EEG became isoelectric (flat). The mean arterial BP (MAP), EEG and ECG were recorded. Twenty-one rats were divided randomly into control, single LBNP exposure, and three LBNP exposures groups (n = 7 in each group). Brain samples were analyzed for Na+,K+-ATPase activity, Na+, K+ and water contents 1 h after single and three 2-min LBNP exposures (-4.00 kPa at a rate of 0.67 kPa x s(-1)), respectively.
  
  
  RESULTS
  MAP decreased rapidly during LBNP exposure. The mean time to isoelectric EEG was 41.33 +/- 11.48, 30.67 +/- 3.88 and 25.67 +/- 3.45 s during -2.67, -4.00 and -5.33 kPa LBNP, respectively. Heart rate (HR) significantly decreased when EEG became isoelectric. MAP, HR and EEG rapidly returned after releasing LBNP. The brain Na+,K-ATPase activity decreased significantly after single LBNP exposure and decreased further after three LBNP exposures. The brain K+, Na+ and water contents increased significantly after three LBNP exposures.
  
  
  CONCLUSIONS
  A rat model of short-term, repeatable brain ischemia was developed using rapid LBNP. Three -4.00 kPa LBNP exposures (2 min each) cause a significant reduction in brain Na+,K+-ATPase activity and brain edema in rats.
authors.affiliation: Department of Aerospace Biodynamics, Faculty of Aerospace Medicine, Fourth Military Medical University, Xi'an, PR China. kyxhd@fmmu.edu.cn
authors.forename: Xi-Qing
authors.initials: XQ
authors.lastname: Sun
authors.forename: Li-Fan
authors.initials: LF
authors.lastname: Zhang
authors.forename: Xing-Yu
authors.initials: XY
authors.lastname: Wu
authors.forename: Shi-Zhong
authors.initials: SZ
authors.lastname: Jiang
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002545:Brain Ischemia / Q000378:metabolism*; D002498:Centrifugation; D004562:Electrocardiography; D004569:Electroencephalography; D006339:Heart Rate; D008150:Lower Body Negative Pressure; D023421:Models, Animal; D011188:Potassium / Q000378:metabolism; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012008:Recurrence; D012964:Sodium / Q000378:metabolism
chemical_list: D012964:Sodium; D000251:Adenosine Triphosphatases; D011188:Potassium