Receptors quite readily remodel in response to external factors. It is one of the things antidepressants do.

To me it's kind of the biggest red flag here, if it's really about receptors then autism should be far more plastic than it is currently defined to be (which is kind of silly since at the moment any sign of plasticity puts you outside one of the hard criteria for an autism diagnosis - so almost definitionally, it can't be the answer).