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DEVELOPMENT OF THE BLOOD‐BRAIN BARRIER FOR 6‐HYDROXYDOPAMINE

The postnatal development of the blood‐brain barrier for the neurotoxic action of 6‐hydroxydopamine on central noradrenaline neurons has been investigated by recording the in vitro uptake of [3H]noradrenaline in slices from cerebral cortex, hypothalamus and spinal cord in rats treated with large doses of 6‐hydroxydopamine at different ages. The [3H]noradranaline uptake was permanently and markedly reduced in all regions when the animals were treated at birth, certainly related to degeneration of noradrenaline neurons, caused by 6‐OH‐DA. In the cerebral cortex and hypothalamus an efficient protection against the effects of 6‐OH‐DA on [3H]noradrenaline uptake developed postnatally, while in the spinal cord this protection was never seen to become complete. The results obtained indicate a rapid formation of a blood‐brain barrier for 6‐OH‐DA in the cerebral cortex between the 7th and 9th day after birth. In the hypothalamus the development of this barrier seemed to have a more gradual time‐course, but appeared to be fully developed already at day 5 postnatally. Also in the spinal cord the barrier developed more gradually from birth to the adult age. It was observed, however, that both in the cerebral cortex and in the spinal cord, the blood‐brain barrier developed, could not completely protect the central noradrenaline neurons from the neurotoxic actions of large doses of 6‐OH‐DA administered systemically to adult rats. Furthermore, the results obtained support the view that 6‐OH‐DA does not seem to apparently affect the outgrowth of remaining NA neurons which have not been destroyed by the 6‐OH‐DA treatment.