Some are noting that this is "in mice", but a recently approved new drug for schizophrenia suggests that a connection between mucins and brain function in humans is more than speculative: https://en.wikipedia.org/wiki/Xanomeline/trospium_chloride

Brand name Cobenfy, this drug is a combination of a muscarinic agonist and a muscarinic antagonist. Notably its therapeutic component was initially developed as an alzheimer's treatment, and IIRC showed positive results in the few trials that were performed in the 90's before the drug was abandoned due to side effects (until now).