LESS STRESS, FOR MICE AND OPERATOR: Testing is carried out in Topcat’s unique and patented one-dimensional runs which maximise access to the plantar area, because the mice can sit comfortably and sideways to the operator. The force is then applied by rotating the transducer via the black handles, which is comfortable for the operator with the elbows supported on the bench.
THE MAXIMUM FORCE IS LIMITED to 7 grams by the design of the probe. We consider one quarter of the body weight to be a realistic maximum force to apply for a threshold response. Above this, you are probably just lifting the leg, so the MouseMet probe buckles (like a filament) above this force and an over-range light glows on the transducer, telling the operator to stop, allow the mouse to settle, and then to try again.
HOT and COLD THRESHOLD TESTING can also be carried out in the same runs, using MouseMet Hot and MouseMet COLD. This saves time and reduces stress, compared with a hotplate or tail flick test, because the mice do not need to re-acclimate.
“Mousemet EvF provided our behavioral endpoint to quantify tactile allodynia and its attenuation in this mouse CIN model. It is a terrific piece of instrumentation that has led us to a novel approach for treating CIN.” Dr K Sufka, Professor of Psychology, Pharmacology & Philosophy, University of Mississippi.
PRICES for MouseMet EvF start at £2350 for a complete system with two runs (expandable later).
BACKGROUND: Mechanical threshold testing on mice and rats is usually carried out using von Frey filaments. They are simple to use and, as long as they are in good condition, will apply the force reliably. But the process is time consuming, requiring several readings to produce one result and some analysis to extract the threshold force from the data. The data are also non-parametric: the threshold forces that result from the popular up-down” method are a discrete range of values and this should be taken into account when analysing the results statistically.
Not surprisingly, several companies have produced “electronic von frey systems” in an attempt to replace the use of several von Frey filaments with a single, analog test consisting of a force ramp to threshold and a peak-hold of the value reached. These electronic force transducers, while useful for larger animals, have not yet gained wide acceptance for mechanical threshold testing in mice (or rats). Click here for a discussion of the tradeoffs.
MouseMet is the only system with a force range (0.1-7gf) entirely suited to mice, mechanical and thermal modalities with transducers that compensate for hand tremor in all three axes and a one-dimensional run system that encourages the mice to sit in the right direction for the test.
MOUSEMET’S ONE DIMENSIONAL RUNS are wide enough for the mouse to feel comfortable in, thereby ensuring natural behaviour, but not wide enough to turn round in without standing up. So, for the vast majority of the test session (after the initial exploratory behaviour), the mouse will be pointing left to right (or right to left).
THE RUNS HAVE BARS which are sized and spaced specifically for the mouse’s paws, allowing him to grip comfortably with his toes but allowing the maximum plantar area for testing with both the mechanical and the thermal probe.
MOUSEMET IS SUPPLIED WITH TWO RUNS and a height adjustable stand. Additional runs and stands may be purchased to save more time; the next two or four mice can be exploring while you test the current four. RatMet is supplied with a run and stand for one rat. All the runs and stands are suitable for laboratory sterilisation procedures.
THE STANDS ARE ADJUSTABLE, in 2cm click steps, so that, when you are sitting at the bench with your elbows on the table, the bars of the run will be at eye level. The sides of the run are transparent, so you have a clear view of the mouse’s paws and the probe. It also means that your hands will be at the right height to operate any of the MouseMet transducers.
All three, Hot, Cold and Mechanical use the same design with different measurement arms. This reduces training time as, once you have familiarised themselves with one transducer, you can easily operate the other. The innovative design makes it insensitive to slight hand tremor; MouseMet EVF can apply forces down to 0.1g without any difficulty while Mousemet HOT and COLD both have application forces at the probe tip of less than 1g.
For all three stimulii, the instrument is held with the probe arm horizontal, the probe tip is touched onto the plantar surface, and the black handles rotated. This is intrinsically easy and comfortable with the forearms supported on the bench and gives full control over the placement of the probe tip. Click here for the data sheet for all three systems.
Hand tremor in the horizontal plane (front to back or side to side) can also affect a reading because it can lead to the probe tip sliding sideways or scratching across the plantar surface, especially at touch-on. This is not problem with von Frey filaments because they are flexible in this direction, even before they reach their buckling force but it can be an issue with a rigid force transducer.
MOUSEMET EvF has a probe tip which is similar to a filament but operated always below its buckling force, so it’s flexible and absorbs slight side to side movement. In addition, it has a 90 degree bend which means that, over the first few millimetres (or 0.5 grams force) of operation, it’s even softer, increasing the chance of placing the filament successfully on the plantar surface without generating a touch-on response.
REPEATABLE BETWEEN OPERATORS:
The last force ramp is displayed as soon as the thumbswitch is pressed and the peak force calculated. Reject tests are inevitable, because the mouse moved, the probe slipped or just because the scientist wasn’t sure if it was a valid response. We’ve watched people trying to achieve a pre-determined force ramp rate, by watching guide lights, or symbols on a computer screen. This really isn’t practical; you should be watching the mouse.
So MouseMet overlays the nominal force rate (1gf/sec) onto the test result displayed.
MouseMet and RatMet are available for outright purchase. For details please call Dr Michael Dixon on +44 (0)7739913696 or email email@example.com.