Asphyxia, cardiac arrest and resuscitation in rats. II. Long term behavioral changes.

This study in 53 rats was conducted to investigate a mild insult, sensitive parameter model in contrast to a severe insult, severe damage model of brain resuscitation. Up to now, the latter approach, which causes neuropathologic changes and neurological abnormalities, has not provided unequivocal data on pharmacological measures to ameliorate post-anoxic brain damage, because of logistical difficulties and many extracranial complicating factors. As tracheotomy and oral intubation in rats proved impractical in studies on recovery from asphyxia, transtracheal jet ventilation was tested in 14 rats as a measure for effective prolonged and reversible control of airway and ventilation. Subsequently, in 37 other rats we studied, during the first post-insult week, the effects of anesthesia, with or without 6 min asphyxia, on behavior, i.e. unrestrained spontaneous locomotor activity and two sessions of one-trial passive avoidance. Transtracheal jet ventilation proved a reliable method for reversible and prolonged controlled ventilation in rats. Spontaneous locomotor activity was affected for at least 48 h after anesthesia and differently so after asphyxia. Passive avoidance was affected only after asphyxia. The recovery of behavior was delayed for days, whereas the recovery of neurologic deficits was only delayed for several post-asphyxia hours. The asphyxiated rats showed hyper-excitability for at least 2 weeks. The existence of abnormal behavior during recovery from mild anoxic-ischemic insults to the brain provides parameters for evaluation of therapies of the post-resuscitation disease in a model without the difficulties encountered in models with severe insults, which made post-insult intensive care necessary. The mild insult, sensitive parameter model is promising and further work in this direction is indicated.