Hello
We are not getting good responses to either CPP (conditioned place preference) or von Frey with CD-1 mice. We are using morphine at 10mg/kg in 100µL as the positive conditioning but the mice are not developing a preference for the associated chamber. Any ideas out there?
We are using a dorsal paw injection of a 50% dilution of CFA in 20µL (0.5mg/mL). Unfortunately we are not seeing an increase in sensitivity in the affected paw. In some cases, there is not response at all to the von Frey filament.
We seriously need ideas. Be advised that the ACC here is not a fan of plantar injections in mice, so I would rather try something else.
Hi Heidi, can you share more about your experiment(s)? Are these two different experiments: (1) Morphine (10 mg/kg, i.p.?) CPP and (2) CFA-induced von Frey hypersensitivity?
If so, what sort of chambers are you using for the morphine CPP? Are the chambers discriminable? Is it biased or non-biased? Does the apparatus work for some positive control drug like cocaine? Why is the injection volume (100 ul) so low for i.p. injections? How long after morphine are they placed in the chambers and how long are they conditioned for each day? How many pairings? Are there any odors?
For the CFA experiment, how long post-CFA are you testing the mice? Sometimes mechanical hyperalgesia takes a few days to reach peak onset. Have you tested the mice with another stimulus like heat? Do the paws swell and look inflamed to match the expectation of CFA injection? If you are not limited to CFA, there are plenty of other manipulations out there that can induce hypersensitivity. Is the von Frey experiment just for hypersensitivity or are you combining this with CPP somehow? The 50% dilution and 20 ul matches convention, are you sure the product is within expiry date and that you are agitating the sediments in the vial prior to mixing with saline and administering?
Hello Justin
It's 2 experiments for the same project. The morphine is to develop a preference for (at present) visually differentiated chambers. Currently we have 25 x 25 cm square chambers with walls 25 cm high with either horizontal or vertical black and white stripes. Today we added mesh to the floor of one chamber but the mice seem to have a preference for that over the smoother plastic waffle board floor. The injections are subQ rather than IP with the morphine, and that seems to be about what everyone uses. We are trying to keep odours to a minimum, along with changes in light levels, noise, etc. The mice were tested naive for innate preference and then paired chamber + saline in the am, with paired opposite chamber + morphine in the afternoon. Morphine is 10mg/kg. Conditioning is for 30 minutes each time, each day for 3 days, then checked to see if a preference developed. Unfortunately, it didn't. I do the injections and place the mouse immediately in the chamber.
For the CFA experiment, the mice were still partially anesthetized when placed in the von Frey, tested at 30, 60, and 120 minutes after injection on the first day, and then tested in a similar time frame for 7 days. The day after the injection, some of the mice showed some swelling of the injected paw, but not as much inflammation as I had expected to see. The mice had usually normal responses on the contralateral side, but frequently no response on the ipsilateral side at all. And the more swelling, the less the response. This week we are trying with a Hargreaves unit, after some practice to make sure we are getting it right.
Eventually, the idea is to test drug candidates, and learn more about mGluR5 receptors.