Dear Heba, I used 5% DMSO in the past as a maximum concentration for IV injections (not IP) in rodents in short duration tox studies to help dissolution of compounds with poor solubility but DMSO was only part of the vehicle used. I would therefore recommend you to work on a vehicle composition which includes DMSO and associate it with something else. And of course, the less concentrated in DMSO, the better it will be !

DMSO is definitly toxic. I don't know the objective of your study but don't forget to evaluate the effect of your vehicle alone (which will contain DMSO). you therefore have to include animals injected with saline (as an absolute control group), animals with your vehicle containing DMSO, and animals treated with rolipram...

Hope this will help you. 

DMSO: Many Uses, Much Controversy

Maya Muir

Abstract

Dimethyl sulfoxide (DMSO), a by-product of the wood industry, has been in use as a commercial solvent since 1953. It is also one of the most studied but least understood pharmaceutical agents of our time--at least in the United States. According to Stanley Jacob, MD, a former head of the organ transplant program at Oregon Health Sciences University in Portland, more than 40,000 articles on its chemistry have appeared in scientific journals, which, in conjunction with thousands of laboratory studies, provide strong evidence of a wide variety of properties. (See Major Properties Attributed to DMSO) Worldwide, some 11,000 articles have been written on its medical and clinical implications, and in 125 countries throughout the world, including Canada, Great Britain, Germany, and Japan, doctors prescribe it for a variety of ailments, including pain, inflammation, scleroderma, interstitial cystitis, and arthritis elevated intercranial pressure.

Yet in the United States, DMSO has Food and Drug Administration (FDA) approval only for use as a preservative of organs for transplant and for interstitial cystitis, a bladder disease. It has fallen out of the limelight and out of the mainstream of medical discourse, leading some to believe that it was discredited. The truth is more complicated.

http://www.dmso.org/articles/information/muir.htm