Blockade of Brain AdrenoreceptorsDelays Seizure Development during Hyperbaric Oxygen Breathing

The main prodromal sign of seizures developing when breathing hyperbaric oxygen is a high activity of sympathetic outflow, as manifested in altered external respiration, impaired cardiac and vascular activity. We tested the hypothesis that the brain adrenergic receptors, as part of the central adrenergic system, are involved in the development of sympathetic hyperactivity and generalized seizures during hyperbaric oxygen breathing. In experiments on rats, α- and β-adrenoreceptors were blocked by non-selective and selective antagonists (propranolol, atenolol, phentolamine and prazosin) injected into the cerebral ventricles. Reactions of the CNS and autonomic nervous system to oxygen breathing at 5 ATA were evaluated. We found that in animals with intact adrenoreceptors, hyperbaric oxygen caused convulsions preceded by biphasic reactions of the cardiovascular system, external respiration and cerebral blood flow. All antagonists used in experiments attenuated visceral reactions and the development of oxygen convulsions, although propranolol showed most pronounced antihypertensive and anticonvulsant properties. The data obtained indicate the involvement of brain adrenergic receptors in the ANS reactions to hyperoxia and in the mechanisms underlying the development of oxygen seizures during hyperbaric oxygen breathing. Our results can be used to develop new methods for the prevention of seizures under extreme hyperoxia and to ensure the safe use of hyperbaric oxygen in clinical practice and diving.