Deepak Subramanian recommendation is indeed a great direction, brainslicemethods.com offer serval ways to deal with this, deppending on the research question.
The simplest way that you could try is by using modified aCSF where NaCl is replaced by the same amount of Choline Chloride (I personally used approx. 125 mM) in the same way that you would use the non-modified aCSF as your cutting medium. Make sure that cutting solutions are ice-cold and of a sorbet consistency and you might be even able to skip the perfusion. If that works out in your hands, you might consider lowering the Choline concentration by dilluting it with non-modified aCSF (NaCl containing aCSF).