Dopamine itself can't cross the blood-brain barrier, but its precursor levodopa can, and once in the brain, levodopa is converted to dopamine by dopa decarboxylase, most importantly within the remaining nigrostriatal neurons.

多巴胺本身不能通过血脑屏障，但它的旋多巴可以，一旦入脑中，旋多巴多巴脱羧酶转换为多巴胺，尤其是在残存的黑质纹状神经元内。

I don't have to keep saying nigrostriatal and mesocortical.

我不必一直说黑质纹状和中皮质。