Carbogen inhalation opens the blood-brain barrier in rats without causing long-term metabolic or neurological deficit.

The blood-brain barrier (BBB) prevents many drugs from entering the brain. Yet, conventional methods that open the BBB are technically demanding, poorly reversible, and can be associated with long-term adverse effects. In comparison, carbogen, which is introduced nearly a century ago as a treatment for psychiatric disorders, is easy to administer and readily available to many labs and hospitals. Here, we show that carbogen inhalation opened the BBB in rats, as indicated by the extravasation of an intravenous protein tracer. When the tracer was injected immediately or hours after carbogen inhalation, less tracer was detected in the rat brains, suggesting at least partial reversibility of this response after carbogen exhalation. Despite marked increase in BBB permeability, inhalation of carbogen for 30-90 min had no acute effect on the level of neuroinflammation or apoptosis in the brain, and had no long-term effect on body weight, food intake, locomotor activity, or learning and memory performance. Our study demonstrated that carbogen inhalation is a safe method to open the BBB.