Mechanical ventilation triggers hippocampal apoptosis by vagal and dopaminergic pathways.

RATIONALE: Critically ill patients frequently develop neuropsychological disturbances including acute delirium or memory impairment. The need for mechanical ventilation is a risk factor for these adverse events, but a mechanism that links lung stretch and brain injury has not been identified.
OBJECTIVES: To identify the mechanisms that lead to brain dysfunction during mechanical ventilation.
METHODS: Brains from mechanically ventilated mice were harvested, and signals of apoptosis and alterations in the Akt survival pathway were studied. These measurements were repeated in vagotomized or haloperidol-treated mice, and in animals intracerebroventricularly injected with selective dopamine-receptor blockers. Hippocampal slices were cultured and treated with micromolar concentrations of dopamine, with or without dopamine receptor blockers. Last, levels of dysbindin, a regulator of the membrane availability of dopamine receptors, were assessed in the experimental model and in brain samples from ventilated patients.
MEASUREMENTS AND MAIN RESULTS: Mechanical ventilation triggers hippocampal apoptosis as a result of type 2 dopamine receptor activation in response to vagal signaling. Activation of these receptors blocks the Akt/GSK3β prosurvival pathway and activates the apoptotic cascade, as demonstrated in vivo and in vitro. Vagotomy, systemic haloperidol, or intracerebroventricular raclopride (a type 2 dopamine receptor blocker) ameliorated this effect. Moreover, ventilation induced a concomitant change in the expression of dysbindin-1C. These results were confirmed in brain samples from ventilated patients.
CONCLUSIONS: These results prove the existence of a pathogenic mechanism of lung stretch-induced hippocampal apoptosis that could explain the neurological changes in ventilated patients and may help to identify novel therapeutic approaches.