osmotic pumps are delivering a drug at a constant rate, are relatively small and if you don't have to infuse into the brain, their installation is rather easy. so I would say this would be the best choice. it may also depend on the type of experiment and stimulation you have to perform.

Hi there, its depend on your experiments, if you are trying to look at the effect of drug on behavior then most of the time antidepressants dissolved in drinking water for chronic treatments. If you are more interested on the molecular studies like receptor mediating binding sites of the drug without affecting the metabolic functions then direct infusion of these drug may be the other option by implanting the cannulae in the vein or directly in the part of the brain (some time the cannulae damage the brain, so choose small size). take a look at this article for the direct infusion of the drug.

http://jpet.aspetjournals.org/content/235/3/619.long

hope this help

good luck