The overall goal of this procedure is to train mice with a four M specific motor skill. This provides a good behavioral model to assess motor learning and memory. In mice, the first step is to allow mice to become familiar with the training chamber and food pellets.
Next food pellets are put within reach of the shaping slit, and the preferred for limb used for retrieval is determined after the shaping period. The mice are trained with the single pellet reaching task and the number of correct reaches with the preferred paw is recorded. Ultimately, this protocol provides a behavioral paradigm to study brain changes at many levels during motor learning and memory formation.
This method can help answer key questions in the neuroscience field, such as how motor learning correlates with structural plasticity and molecular alterations in the mouse brain, and how various neurological diseases perturb fine motor skills For the best results. Perform this task in a quiet location away from any noise or distractions. A custom made clear plexiglass training chamber that contains three vertical slits is used for shaping and training.
One slit is on the shaping edge and two slits are on the opposite training edge to hold the millet seeds in place during the shaping sessions constructed a tilted tray from three glass slides. A food platform is used during the training sessions. Divots on the left and right sides of the platform hold the millet seed in place.
These divots correspond to the left and right slit in the mouse training chamber and are used for the training of dominant for lims. Other items useful to have on hand during the procedure are forceps, a scale and a stopwatch. Two days before beginning the shaping procedure food restrict the animals to maintain a reduced body weight of about 90%of baseline on day one.
Placed two mice into the training chamber at the same time, and allow them to habituate. Place approximately 20 mil seeds per mouse inside the chamber and allow the mice to explore for 20 minutes. On the next day, place the animals into chambers individually and provide each with approximately 20 mil seeds the following day.
The shaping edge is used to determine for limb dominance. Place the single slit side of the chamber facing downwards. Next, press the food tray filled with millet seeds up against the front wall of the training chamber.
When ready, place a single mouse in the chamber. Allow the animal to retrieve seed through the training slit and record the for used for the retrieval. The shaping period is considered finished when two criteria are met.
First, the mouse conducts 20 reaching attempts within 20 minutes. Second, more than 70%of these reaches are performed with one four limb. If the mouse uses its tongue to get the seeds into the chamber, move the tray back slightly to encourage four limb reaching.
If the mouse cannot finish shaping within a week, drop it from the experiment To begin the training session, configure the training chamber with the double slit face downwards. When ready, place the mice individually into the cage. Put individual seeds on the food platform in the divot corresponding to the preferred paw determined during the shaping period.
Once the seed is in place, observe the mouse's reaching behavior and score the results. A success is scored when the mouse reaches with the preferred paw, retrieves and eats the seed. Score a drop when the mouse reaches with the preferred paw, grasps the seed, but drops it before putting it into its mouth.
If the mouse reaches for the seed with the preferred paw, but either misses it or knocks it off the holding plate, it is scored as a fail. A mouse may reach even when there is no seed placed on the food platform. These are considered in vain reaches and are not counted towards.
The total number of reaching attempts to discourage in vain reaches train mice to walk back to the other end of the training chamber before placing the next seed. If a mouse reaches with the non-preferred paw, these reaches are considered contralateral reaches and are not counted towards the total number of reaches. Train the mice daily for 30 reaching attempts on the preferred limb, or 20 minutes, whichever comes first.
After the daily training session, return the mice to their home cage. Body weights of mice should be closely monitored throughout experiments. Body weight loss for a single mouse during food deprivation shaping and training is shown here.
These results show that the average success rate improves over the training period as well as the average speed of success. Success rates for an overs shaped and a non learning mouse are plotted here. This graph compares the motor performance of pre-trained versus naive adult mice during a four day retraining period.
While attempting this procedure, it's important to remember to standardize animal testing conditions. This can be done by minimizing environmental perturbations, having the same trainer, handling the same mouse, and training at the same hours within the day throughout the experiments.
