Eric Kandel trained as a psychiatrist, sometime back in the Dark Ages.
Things are a bit different today, though. Biology is ultra-specialized, and you need a lot of training to get anywhere.
If you are interested in working with Aplysia, I would suggest you get a Ph.D., or at least some basic research training while you are in med school.
If you are interested in clinical psychiatry or psychology, I don't think you'll find much cellular/molecular biology there once you get out of school.