Effects of acute hypoxia on neonatal rat brain: regionally selective, long-term alterations in catecholamine levels and turnover.

Neonatal rats were exposed to 2 hr of hypoxia (7% O2) on the day after birth and examined for effects on development of noradrenergic and dopaminergic systems. Measurements were made of transmitter levels and turnover, the latter a biochemical index of neuronal activity. Hypoxia had a regionally selective effect, characterized by a long-lasting increase in turnover of norepinephrine and dopamine in midbrain and brainstem, with little or no effect in cerebral cortex or cerebellum. The effects of hypoxia were exacerbated when peripheral alpha-adrenergic receptors were blocked with phenoxybenzamine during the hypoxic exposure; in this case, the same abnormalities were then seen in the cerebral cortex as well. Thus, the release of peripheral catecholamines during the hypoxic insult, and their actions at alpha-adrenergic receptors, may play a role in protecting the neonatal nervous system from hypoxia-induced alterations.