The Dose-dependent Effect Of Naloxone On The Outcome Of Severe Fluid-percussion Brain Injury In Rats And Its Protective Mechanism

The abnormal increase of endogenous opioid peptide concentration in brain tissue and plasm may cause delayed injury after traumatic brain injury (TBI) has been found in recent years. Nonspecific opiate antagonist naloxone showed effective protection in TBI. The outcome were different for the dose of naloxone used in animal test and clinic varied greatly(0.01-30mg/kg). We try to investigate the dose-dependent effect of naloxone on the outcome of severe fluid-percussion brain injury in rats. Male Sprague-dawley rats (n=150), weighing300-350 gm each, were trained for beam walking test, beam balance test, memory test before experiment. 4 hours prior to trauma, animals were surgically prepared for fluid-percussion brain injury under intraperitoneal sodium pentobarbital anesthesia (54 mg/kg) by attaching a hollow injury tube (2.6 mm inside diameter) epidurally over a trephined hole on the sagittal suture midway between the lambda and bregma. A fluid percussion device offered by medical department of Virginia commonwealth University U.S.A. was used to produce severe brain injury (pressure pluse 2.0-2.1 atm). Rats showed neurological signs of areflexia, coma, and stupor more than 10 minutes. 104 survived animals 20 minutes afterinjury were randomly divided into four groups, Saline (control-group), 0.03mg/Kg (low dose-group), 0.3mg/Kg (moderate dose-group), 3mg/Kg (high dose-group) of naloxone were injected intraperitoneally once every day for 7 days after injury. Beam walking test, beam balance test, memory test were performed every day after injury to evaluate neurologic functions. 8 rats were decapitated 48 hours after injury in each group. Wet and dry weights(100℃,24hours) of cerebral hemisphere were measured on electronic balance to calculate the contents of brain tissue water by formula Elliot. 2 rats were sacrificed to take out hippocampus for pathological slice and electronic microscope to observe the neurons change in each group at 48 hours and 15 days after injury. Side-effects were observed , including skin eruption, lesions of heart, lung, liver, kidney. Pathological slices were performed with heart, lung, liver, kidney30 days after injury. All data were assessed by repeated measurement of analysis of variance of SPSS. Results: Neurobehavioral outcome: Moderate and high dose of naloxone group showed significant improvement compared to low dose and control group in beam walking test, beam balance test, memory test (P<0.05). The contents of brain tissue water in moderate and high dose of naloxone group significantly decreased (P<0.05). Pathological changes: In low dose and control group, part of hippocampus had unreversible changes. acidophilus neurons had decreased size, nissl body disappeared, mitochondrionvacuolated, chromatin dissolved in nucleus. In moderate and high dose group, organell had less swelling, endoplasmic reticulum, ribosome mitochondrial cristae, chromatin remained. Conclusion: Early application of moderate to high dose (0.3-3mg/kg) of naloxone is effective to improve the outcome of traumatic brain injury, which provides significant evidence for clinical use of naloxone.