Methamphetamine-induced conditioned place preference in LG/J and SM/J mouse strains and an F45/F46 advanced intercross line

Abstract

The conditioned place preference (CPP) test is frequently used to evaluate the rewarding properties of drugs of abuse in mice. Despite its widespread use in transgenic and knockout experiments, there are few forward genetic studies using CPP to identify novel genes contributing to drug reward. In this study, we tested LG/J and SM/J inbred strains and the parents/offspring of 10 families of an F(45)/F(46) advanced intercross line (AIL) for methamphetamine-induced CPP (MA-CPP) once per week over 2 weeks. Both LG/J and SM/J mice exhibited significant MA-CPP that was not significantly different between the two strains. Furthermore, LG/J mice showed significantly less acute MA-induced locomotor activity as well as locomotor sensitization following subsequent MA injections. AIL mice (N = 105) segregating LG/J and SM/J alleles also demonstrated significant MA-CPP that was equal in magnitude between the first and second week of training. Importantly, MA-CPP in AIL mice did not correlate with drug-free or MA-induced locomotor activity, indicating that MA-CPP was not confounded by test session activity and implying that MA-CPP is genetically distinct from acute psychomotor sensitivity. We estimated the heritability of MA-CPP and locomotor phenotypes using midparent-offspring regression and maximum likelihood estimates derived from the kinship coefficients of the AIL pedigree. Heritability estimates of MA-CPP were low (0-0.21) and variable (SE = 0-0.33) which reflected our poor power to estimate heritability using only 10 midparent-offspring observations. In sum, we established a short-term protocol for MA-CPP in AIL mice that could reveal LG/J and SM/J alleles important for MA reward. The use of highly recombinant genetic populations like AIL should facilitate the identification of these genes and may have implications for understanding psychostimulant abuse in humans.

Keywords: addiction; amphetamine; cue-associated craving; drug abuse; locomotion; pavlovian conditioning; psychostimulants; reinforcement.

FIGURE 1

Schematic of the MA-CPP protocol. We used a 15-day protocol whereby mice were assessed for initial preference for the drug-paired side (D1, initial preference), trained for two separate 4-day sessions with alternating injections of MA and SAL in the respective contexts (D2–D5; D9–D12) and assessed for MA-CPP on Day 8 (D8) and Day 15 (D15). Each day represents a 30 min session. Day, day of the protocol; Tx, treatment for that day; SAL, saline treatment; MA, methamphetamine treatment; -, mice were left undisturbed in their home cage in the vivarium on these days.

FIGURE 2

MA-CPP and MA-ACT in LG/J, SM/J, and AIL mice. (A,E) Time spent on the MA-paired side (s) on D1 and then on D8 and D15 following alternating MA and SAL trials. LG/J mice (N = 31) are represented by white bars, SM/J mice (N = 31) are represented by the black bars, and AIL mice (N = 105) are represented by gray bars. (B,F) Locomotor activity (total distance traveled in cm; summed over 30 min) in LG/J (white circles), SM/J (black circles), and AIL mice (gray circles; N = 105) during days of preference assessment. (C,G) MA-induced locomotor activity during MA training trials (D2, D4, D9, and D11) in LG/J, SM/J, and AIL mice. (D,H) Locomotor activity during SAL training trials (D3, D5, D10, and D12) in LG/J, SM/J, and AIL mice. *Significantly different from D1 (A,B,E), D2 (C,G), or D3 (D,H). ^#Significantly different from SM/J (C,D). ^%Significantly different from D4 (B) or D5 (C). All significant results were Bonferroni-corrected for multiple comparisons across days (see Results).

FIGURE 3

Preference and locomotor activity in a SAL control experiment in AIL mice. (A) Time spent on the drug (left)-paired side on D1 and on D8 and D15 following training with SAL administration in both sides of the CPP apparatus in AIL mice (N = 32). (B) Locomotor activity (centimeter) during the training trials where mice received SAL each day (D2–D5; D9–D12).

FIGURE 4

No correlation of MA-CPP with MA-ACT in AIL mice. (A,B) Scatterplot of the average amount of MA-induced locomotor activity on D2 and D4 of training (MA-ACT) versus the time spent on the drug-paired side on D8 (A; D8 MA-CPP) or versus the difference in time spent on the MA-paired side between D1 and D8 (B; D8-D1 MA-CPP) in AIL mice (N = 105). (C) Scatterplot of MA-ACT versus the average amount of SAL-induced locomotor activity during D3 and D5 of training (SAL-ACT) in AIL mice. r, Pearson’s correlation coefficient. *p < 0.05.