Place Conditioning Preference is most often used with rodents (rats, mice) to study the positive (rewarding) or negative (aversive) motivational effects of objects (e.g., food pellets, novel toys) or experiences (e.g., brain stimulation, drug intoxication, drug withdrawal, foot shock, illness, wheel running and copulation).
Although a number of different designs and apparatuses are used in this model, the basic characteristics of this task involve the association of a particular environment with drug treatment, followed by the association of a different environment with the absence of the drug (i.e., the drug’s vehicle).
The design consists of a two-compartment chamber connected by a doorway being designed to have different characteristics (e.g., white vs. black walls, pine vs. corn bedding, and horizontal grid vs. cross-grid flooring). The gate between the compartments can be opened to allow an animal to pass freely between them.
During training, an animal (typically a rat or mouse) is given an injection of a drug with potentially rewarding or aversive properties, and is then placed into one of the compartments for several minutes. On the following day, the rat is injected with the drug’s vehicle and then placed in the opposite compartment. Generally, these daily sessions alternate between drug and vehicle for 2 or 3 days each. Afterward, a test session is conducted, which consists of placing the animal in the center compartment and then, after opening the gate, recording the time the animal spends in each of the compartments during the session.
A conditioned place preference (CPP) is found if the animals spend significantly more time in the drug-paired compartment versus the vehicle-paired compartment. On the other hand, if the animals spend significantly more time in the vehicle-paired compartment versus the drug-paired compartment, then this is considered a conditioned place aversion (CPA). Typically, drugs of abuse, such as cocaine, produce CPP, and drugs that elicit aversive effects, such as lithium chloride, produce CPA.
There are some limitations with this test, however, primarily the problem of not knowing exactly what is being evaluated. It could be, instead of a preference or aversion, that the drugs are affecting locomotion vs. sedation. If a drug happens to increase activity, it could be that the animal goes to explore the drug-paired environment more. The drugs could also make the drug-paired compartment seem more novel, so the animal will want to explore that more.
Other resources
Workflow
(Christopher L Cunningham, Christina M Gremel & Peter A Groblewski . 2006 . Drug-induced conditioned place preference and aversion in mice. Nature Prorocols 1664 Vol.1 No.4 )
Habituation (day 1)
1 Prepare all conditioning boxes with smooth, white paper floors (e.g., legal-size copy paper).
2 Weigh each mouse and immediately inject (i.p.) with vehicle. Place the mouse into the center of the box and close the sound-attenuating chamber. Record activity.
3 After the 5-min habituation session is complete, remove the mouse from the apparatus and return it to its home cage.
Conditioning (days 2–5, 8–11)
4 Twenty-four hours after the habituation session, initiate the first conditioning session.
5 Prepare conditioning boxes with the appropriate floors (entirely grid or entirely hole floors for each box depending on group, floor and order assignment).
6 Weigh each mouse and immediately inject i.p. with drug (if CS+ trial) or vehicle (if CS trial). Place the mouse into the center of the box and close the sound-attenuating chamber. Record activity during trial.
CRITICAL STEP We strongly recommend that the time delay between opening or moving the home cage and placement of the mouse in the conditioning box be kept as short as possible (e.g., 30–60 s). For reasons that are not entirely clear, we have found that longer delays yield weaker and more variable place conditioning. This interference may be related to timing of stress axis activation in relation to drug exposure or it may reflect some type of associative interference (e.g., overshadowing by pretrial cues). Ideally, the home cage rack should be located within a few steps of the conditioning apparatus in order to minimize the time delay. In situations where the animal colony is located at a distance from the equipment, we recommend moving the animals adjacent to the equipment (in their home cage) and letting them rest at least 1 h before conditioning or testing.
7 After the 5-min conditioning trial is complete, remove the mouse from the apparatus and return it to its home cage. These trials will occur at 48-h intervals (i.e., on days 2, 4, 8 and 10).
8 Twenty-four hours later (or 72 h later over weekend), prepare the boxes with the floor not used in the previous session.
9 Weigh each mouse and immediately inject i.p. with drug (if CS+ trial) or vehicle (if CS trial). Place the mouse into the center of the activity box and close the sound-attenuating chamber. Record activity during trial.
10 After the 5-min conditioning trial is complete, remove the mouse from the apparatus and return it to its home cage. These trials will occur at 48-h intervals (i.e., days 3, 5, 9 and 11).
Preference test (day 12)
11 Twenty-four hours after the final conditioning session, prepare each conditioning box with half grid and half hole floors (counterbalanced position).
12 Weigh each mouse and immediately inject i.p. with vehicle and place the mouse into the center of the box. Close the sound-attenuating chamber and record test activity.
13 After the 30-min preference test session is complete, remove the mouse from the apparatus and return it to its home cage.
CRITICAL STEP To control for odor, the floors and the inside of the box are wiped with a damp sponge (no soap) to disperse any lingering localized odor and the litter paper beneath the floors is changed between subjects.
TIMING
Below is an example of a timeline for the GRID+ conditioning subgroup (drug paired with the grid floor). This timeline illustrates training for a group that receives the drug trial before the vehicle trial. Half of the GRID+ subgroup would receive the vehicle trial before the drug trial (not shown).
Day 1: 5-min habituation session (or 30-min pretest session)
Day 2: 5-min CS+ trial (drug + grid floor)
Day 3: 5-min CS- trial (vehicle + hole floor)
Day 4: 5-min CS+ trial (drug + grid floor)
Day 5: 5-min CS- trial (vehicle + hole floor)
Days 6, 7: 2-day break from conditioning (weekend)
Day 8: 5-min CS+ trial (drug + grid floor)
Day 9: 5-min CS- trial (vehicle + hole floor)
Day 10: 5-min CS+ trial (drug + grid floor)
Day 11: 5-min CS- trial (vehicle + hole floor)
Day 12: 30-min drug-free test (both grid and hole floors)
Below is an example of a timeline for the GRID conditioning subgroup (drug paired with the hole floor). This timeline illustrates training for a group that receives the drug trial before the vehicle trial. Half of the GRID- subgroup would receive the vehicle trial before the drug trial (not shown).
Day 1: 5-min habituation session (or 30-min pretest session)
Day 2: 5-min CS+ trial (drug + hole floor)
Day 3: 5-min CS- trial (vehicle + grid floor)
Day 4: 5-min CS+ trial (drug + hole floor)
Day 5: 5-min CS- trial (vehicle + grid floor)
Days 6, 7: 2 days break from conditioning (weekend)
Day 8: 5-min CS+ trial (drug + hole floor)
Day 9: 5-min CS- trial (vehicle + grid floor)
Day 10: 5-min CS+ trial (drug + hole floor)
Day 11: 5-min CS- trial (vehicle + grid floor)
Day 12: 30-min drug-free test (both grid and hole floors)
