An internet article I received contained this:

A study published in the May 10, 2006 issue of the European Journal of
Pharmacology (http://www.sciencedirect.com/science/journal/00142999) found
that diabetic rats given the antioxidants vitamin E or melatonin
experienced less impairment of memory and learning compared to untreated
diabetic rats. The finding provides support for the theory that oxidative
stress is a culprit in cognitive impairment that occurs with diabetes.

My question is: what do the researchers do to "produce" diabetic rats?