How best to dissolve CNO depends on what it is soluble in (and that depends on the particular polymorph)

I recently received the following question:

"My question is with regard to the use of CNO in drinking water (in mouse studies). Your recipe calls for the addition of a small amount of DMSO to dissolve CNO at a concentration of 5 mg in 200 mL. As we and others routinely dissolve CNO in 0.9% saline (no DMSO) at concentrations up to four times this amount, I am curious whether the addition of DMSO to CNO solutions for H2O drinking is critical, or whether the properties of CNO permit it's direct dissolution in H2O at concentrations from 5-20 mg per 200 mL. There appears to be no difficulty dissolving such concentrations in H2O in my hands, but I would prefer to hear your perspective. Is there a published reference for the solubility profile of CNO in H2O or 0.9% saline?"

It basically depends upon the source of the CNO.  CNO via the NIH RAID program (which is what we use) is not readily soluble in H20 while commercial CNO is.  Although we've verified that both sources are the same compound they likely represent distinct polymorph forms so that one is readily soluble in H20 and the other (e.g. NIH RAID CNO) not so much.

So if you can dissolve in H20 (and it is in solution and not in suspension) go ahead and do so.


  1. Hi, can you share with me where can we purchase the water soluble CNO? Thanks!

  2. Sigma chemical company

    Note that is says that CNO is a 5-HT2 antagonist which is incorrect


  3. Thanks so much Dr. Roth! The Sigma CNO was the one I was going to purchase but wasn't sure about water solubility. I'll get it then :-)

  4. Hi!
    I have a question regarding CNO solubility. We were using last year CNO from Tocris and was well dissolved in saline. We are using DREADD and injecting CNO ip to our mice to activate/inhibit specific neural circuits and then looking for anxiety in the open field or elevated plus maze). However we have received a letter this week from Tocris that says that CNO is no longer soluble in water due to reported precipitation in some cases and they have removed it from the "product information data sheet" and added instead: soluble in DMSO to 50 mM. I am thinking to add from now on DMSO in order to assure that CNO is well dissolved and not having to worry anymore. Since I have never used it with my experiments, I would like to know if there is any problem to change to DMSO+saline (would I be able to compare my previous data with only CNO dissolved in saline?) and if other people is experiencing the same problem and how are they dealing with it. I have been reading that the % of DMSO used to dissolved CNO is between 0.5-10%, which one is more recomended? Thank you very much!

  5. Go to here for detailed visual instructions:

  6. Thank you very much Dr. Roth. That was really helpful!

  7. Hi! I was trying to dissolve CNO as in the listed protocol (0.5 mg/ml in DMSO 0.5 %) but it is not dissolving. Maybe because our CNO is not from NIH but from Tocris... As I had to increase the % of DMSO to 1% to fully dissolve the CNO I have a question regarding the performance in anxiety tests. Has DMSO any effects in anxiety tests? I couldn't find anything in the literature and I think that it is inert but I wasn't not sure. Thank you!

  8. I would recommend doing a no-CNO control where the same amount of DMSO is administered to mice expressing DREADD as well as control (e.g. a 2 x 2 design).

    1. Thank you very much for your recomendation Dr. Roth!

  9. Has anyone else successfully kept CNO in solution for an extended period of time at body temperature? Does the solvent used (DMSO, DI Water, Saline, Ethanol) affect this?


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