RAT CONDITIONED PLACE PREFERENCE (CPP)

Animals

Studies are conducted in adult male and female Sprague Dawley rats (Envigo) in an AAALAC-accredited facility with approval from an Institutional Animal Care and Use Committee, and implemented in accordance with the Guide for the Care and Use of Laboratory Animals 8th Edition (National Research Council, 2011) with standards set by the National Institutes of Health.

Experimental procedure

Conditioned place preference (CPP) is commonly used to measure the rewarding properties of an asset in laboratory animals. A typical study involves pairing the asset with a distinct environmental context (e.g., tactile, visual, and/or olfactory). Following conditioning, a bias to the asset-paired context relative to control indicates that the asset was rewarding.

The CPP test is conducted in appropriate group sizes determined by power analysis. Male and female rats (n=10-20) are evaluated in separate cohorts. Multiple doses are investigated, and vehicle and positive control groups are included to establish the validity of the experiment. For all animals, experimenters are blinded to the treatments, and dosing is performed by an independent experimenter.

CPP study design

During the CPP testing, rats are placed in a divided arena as presented in Figure 1.

The CPP trials are videotaped, and the time spent in each chamber is scored by two independent experimenters blinded to the study design. The CPP study design spans through 10 days, based on Kimmel et al., 2000, as follows:

Baseline preference assessment (Day 1): rats are free to explore the entire testing area freely for 20 minutes, and the time spent in each chamber is recorded. Rats with strong preference for one chamber (spending >75% of time in one chamber) are excluded. Groups are balanced such that the average preference for each chamber approximates chance levels and is the same across groups.

Conditioning (Days 2 to 9): on experimental days 2, 4, 6, and 8, rats are treated with vehicle and confined to one chamber for 20 minutes. On experimental days 3, 5, 7, and 9, rats are treated with the asset and are confined to the other chamber for 20 minutes. For each study, the chambers are paired with the asset or the vehicle in a counterbalanced manner within each group.

Post-conditioning bias test (Day 10): post-conditioning testing is conducted in the absence of treatment (i.e., without asset or vehicle administration). Rats are allowed to explore the testing arena freely for 20 minutes, with the door open, and the time spent in each chamber is recorded.

Experimental outcomes: results are expressed as the percent of time the rat spend in the asset-paired compartment on Day 10. Results are also expressed as change in preference score, defined as the difference of time (seconds) in the asset-paired compartment from Day 1 to Day 10 (D10-D1).

This work was conducted by PsychoGenics Inc. (Paramus, NJ) in collaboration with PSPP, NINDS, NIH under contract # 75N95019D00026