a tight BBB only allows certain drugs thru..mostly a function of
lipid solubility. For example, alcohol and anesthetics pass the
easiest.

In the case of the Zonulin channels, these would allow bacteria thru, and large water soluble substances and peptides. This would be the CNS version of "leaky gut syndrome". Leaky gut was always pooh poohed by doctors and now with the new information, that is no longer that controversial.

Some drugs like H2 antagonists, Zantac and Pepcid, pass the BBB more often in the elderly. They cause a delirium when that happens. That is one example of how the BBB changes with age.