Confounding effects of volatile anesthesia on CBV assessment in rodent forebrain following ethanol challenge

PURPOSE: To compare and contrast the pattern and characteristics of the cerebral blood volume (CBV) response to ethanol (EtOH) in rats under awake and anesthetized conditions. MATERIALS AND METHODS: Acute EtOH (0.75 g/kg) challenge-induced CBV changes were measured using a contrast-enhanced functional MRI CBV method in 15 male Sprague Dawley rats under three experimental conditions: 1.0% to 1.2% isoflurane (N = 5); 0.8% halothane (N = 5); and awake with no anesthetic (N = 5). Physiological parameters were collected from bench settings in nine rats from the above different conditions. Four parameters: 1) area under the curve (AUC%); 2) the maximum signal change (Max%); 3) EtOH absorption rate (alpha(2)); and 4) EtOH elimination rate (alpha(1)) were employed to compare EtOH-induced MRI signals between the awake and anesthetized groups. RESULTS: Both awake and anesthetized animals responded with an increase in CBV to EtOH challenge. However, the presence of anesthesia promoted a significant preferential flow to subcortical areas not seen in the awake condition. CONCLUSION: Unclear mechanisms of anesthesia add a layer of uncertainty to the already complex interpretation of EtOH's influence on neuronal activity, cellular metabolism, and hemodynamic coupling.