it depends on the animal, for mice you can start by 1mL/hour.

and increase slightly and gradually in case of need

How about, for example, amygdala or paraventricular thalamus? What is the maximal volume and rate for infusion?

Then you should know the rate of CSF production and that of CSF absorption and not exceed the difference when you infuse a fluid into the ventricles.

it varying animal to animal, for mice you can start by 20 microliter/min