Midazolam, methamphetamine, morphine and nicotine intake in high-drinking-in-the-dark mice

Abstract

The high-drinking-in-the-dark (HDID) lines of mice were selectively bred for achieving high blood alcohol levels in the drinking-in-the-dark (DID) task and have served as a unique genetic risk model for binge-like alcohol intake. However, little is known about their willingness to consume other addictive drugs. Here, we examined (a) whether the HDID-1 and HDID-2 lines of mice would voluntarily consume midazolam, methamphetamine, morphine and nicotine in a DID test and (b) whether the HDID lines differ from their founders, heterogeneous stock/Northport (HS/NPT), in consumption levels of these drugs at the concentrations tested. Separate groups of HDID-1, HDID-2 and HS/NPT mice were given 4 days of access to each drug, using the single-bottle, limited-access DID paradigm. Male and female mice of both HDID lines consumed all four offered drugs. We observed no genotype differences in 40 μg/ml methamphetamine intake, but significant differences in nicotine, midazolam and morphine intake. Both HDID lines drank significantly more (150 μg/ml) midazolam than their founders, providing strong support for a shared genetic contribution to binge ethanol and midazolam intake. HDID-2 mice, but not HDID-1 mice, consumed more morphine (700 μg/ml) and more nicotine across a range of concentrations than HS/NPT mice. These results demonstrate that the HDID mice can be utilized for tests of voluntary drug consumption other than ethanol and highlight potentially important differences between HDID lines in risk for elevated drug intake.

Keywords: DID; HDID; methamphetamine; midazolam; morphine; nicotine.

FIGURE 1

Both high-drinking-in-the-dark (HDID) lines consumed more midazolam than their HS/NPT founders. (A) Male and female HDID-1, HDID-2, and HS/NPT mice were tested in a modified 4-day drinking-in-the-dark (DID) test with access to midazolam (n = 14–24/genotype). Data are shown collapsed across sex. (B) Analysis of midazolam intake revealed a main effect of genotype (with both HDID lines drinking more than HS/NPT mice), a main effect of day, a main effect of sex (with female mice drinking more than male mice) and a day-by-genotype interaction. Both HDID lines, but not HS/NPT mice, showed a significant effect of day on midazolam intake. Means ± SE shown. *p < 0.05; **p < 0.005; ***p < 0.001

FIGURE 2

High-drinking-in-the-dark (HDID)-1, HDID-2 and HS/NPT mice consumed comparable levels of methamphetamine. (A) Male and female HDID-1, HDID-2 and HS/NPT mice (n = 24–27/genotype) were tested in a 4-day drinking-in-the-dark (DID) test with access to methamphetamine. Data are shown collapsed across sex. (B) Analysis of methamphetamine intake across the 2-h sessions on Days 1–4 revealed a main effect of sex, with female mice drinking more than male mice, and a main effect of day, with mice drinking more on Day 1 than either Day 2, 3 or 4. No genotype effects emerged. (C) During the 4-h access period on Day 4, no significant genotype or sex effects were found. Means ± SE shown. *p < 0.05; **p < 0.005; ***p < 0.001

FIGURE 3

High-drinking-in-the-dark (HDID)-2, but not HDID-1, mice consumed more morphine than their HS/NPT founders. (A) Male and female HDID-1, HDID-2 and HS/NPT mice (n = 22–25/genotype) were tested in a 4-day DID test with access to morphine. Data are shown collapsed across sex. (B) Analysis of morphine intake across the 2-h sessions on Days 1–4 revealed a main effect of day (with mice drinking less on Day 4 than on Day 1) and a main effect of genotype, with HDID-2 mice drinking more morphine than HS/NPT mice. (C) Analysis of the 4-h morphine intake revealed a significant genotype effect, but post hoc comparisons revealed only a trend towards a difference in HDID-2 and HS/NPT intake (as indicated with a +). Means ± SE shown. *p < 0.05; **p < 0.005; ***p < 0.001

FIGURE 4

High-drinking-in-the-dark (HDID)-2, but not HDID-1, mice consumed more nicotine than their HS/NPT founders. (A) Male and female HDID-1, HDID-2 and HS/NPT mice (n = 12–22/genotype) were tested in a 4-day drinking-in-the-dark (DID) test with access to nicotine. Data are shown collapsed across sex. (B) Analysis of nicotine intake across the 2-h access periods across the 4 days revealed a significant effect of day and genotype and a significant day × genotype interaction. Overall, HDID-2 mice consumed more nicotine than did HS/NPT mice. There was a significant effect of day within the HDID-2 mice (but not in HDID-1 or HS/NPT mice), with HDID-2 mice drinking more nicotine on Day 1 than on Day 4. (C) The effect of genotype persisted into the 4-h access period, with HDID-2 mice drinking more than HS/NPT. Means ± SE shown. *p < 0.05; **p < 0.005; ***p < 0.001