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. 2017 Feb 22:11:29.
doi: 10.3389/fnbeh.2017.00029. eCollection 2017.

A Rat Drinking in the Dark Model for Studying Ethanol and Sucrose Consumption

Joan Y Holgate  1 , Masroor Shariff  1 , Erica W H Mu  1 , Selena Bartlett  1
Affiliations

A Rat Drinking in the Dark Model for Studying Ethanol and Sucrose Consumption

Joan Y Holgate et al. Front Behav Neurosci. .

Abstract

Background: The intermittent access 2-bottle choice (IA2BC) and drinking in the dark (DID) models were developed for studying rodent binge-like consumption. Traditionally, IA2BC was used with rats and DID with mice. Recently, IA2BC was adapted to study mouse ethanol consumption. However, it is unknown whether DID is suitable for rats or if one rat model is more advantageous than another for studying binge-like consumption. Methods: Male Wistar rats consumed 20% ethanol or 5% sucrose using IA2BC or DID for 12 weeks. IA2BC drinking sessions occurred on alternate days (Mondays-Fridays) and lasted 24 h, whereas DID sessions ran 4 h/day, 5 days/week (Monday-Friday). Average consumption/session, week and hour was measured. To explore DID model suitability for screening novel compounds for controlling ethanol and sucrose intake, varenicline (2 mg/kg) or vehicle was administered to DID rats. Results: IA2BC rats consume more ethanol/session and similar amounts of ethanol/week than DID rats. While, IA2BC rats consume more sucrose/session and week than DID rats. Although IA2BC rats had more ethanol and sucrose access time, DID rats had greater ethanol and sucrose intake/hour. Varenicline significantly reduced ethanol and sucrose consumption in DID rats, consistent with previously published IA2BC studies. Conclusions: Despite the shorter access time, the rat DID model induced higher initial intake and greater consumption/hour for both ethanol and sucrose. The shorter duration of DID sessions did not prevent detection of varenicline-induced reductions in ethanol or sucrose consumption, suggesting the DID model may be suitable for studying binge-like ethanol and sucrose consumption.

Keywords: consumption model; drinking in the dark; ethanol; intermittent access 2-bottle choice; rat; sucrose; varenicline.

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Figures

Figure 1
Figure 1
Experimental timeline for the intermittent access 2-bottle choice (IA2BC) and drinking in the dark (DID) models. Five week old male Wistar rats are given 1 week to habituate to the experimental housing conditions before commencing consumption of 20% ethanol or 5% sucrose using the IA2BC (A) or DID (B) models. Rats consuming ethanol using the DID model also had blood collected for blood ethanol concentration (BEC) measurement after 10 weeks of drinking sessions. After 12 weeks of ethanol or sucrose consumption, DID rats received 2 once weekly injections of vehicle or 2 mg/kg varenicline in pseudorandom order, such that each rat served as their own control.
Figure 2
Figure 2
Comparison of ethanol consumption per session using the IA2BC and DID models. (A) Rats using the DID model (gray) consumed more 20% ethanol than IA2BC rats (white) following 30 min of ethanol access. (B) However, following 2 h of ethanol access, both the DID and IA2BC rats consumed similar amounts of ethanol. (C) The total amount of ethanol consumed per session was greater for rats using the IA2BC model compared to the DID model. n = 8. Unpaired T-tests with Holm-Sidak correction (alpha = 0.017). #p < 0.017, ####p < 0.0001 compared to IA2BC rats.
Figure 3
Figure 3
Comparison of weekly and hourly ethanol consumption using the IA2BC and DID models. (A) Rats consuming 20% ethanol using the DID (gray) and IA2BC (white) model consumed similar amounts of ethanol per week. (B) However, the average amount of ethanol consumed per hour was greater for rats using the DID model compared to the IA2BC model n = 8 per group. Two tailed unpaired Student’s T-test. ****p < 0.0001 compared to IA2BC rats.
Figure 4
Figure 4
Blood ethanol consumption correlates with ethanol consumption with the DID model. Linear regression and Pearson’s correlation coefficient were used to show that BEC increased with ethanol consumption in rats using the DID model (r2 = 0.591, p = 0.026). n = 8 per group.
Figure 5
Figure 5
Varenicline reduces ethanol consumption in DID rats. Administration of 2 mg/kg varenicline (gray) produced a significant reduction in ethanol consumption 30 min (A), 2 h (B) but not 4 h (C) after the commencement of a standard DID drinking session compared to vehicle (white). n = 8 per group. Unpaired T-tests with Holm-Sidak correction (alpha = 0.017). #p < 0.017, ###p < 0.001 compared to vehicle.
Figure 6
Figure 6
Comparison of sucrose consumption per session using the IA2BC and DID models. Using the DID model (gray), rats consumed similar amounts of 5% sucrose than rats using the IA2BC model (white) following 30 min (A) and more sucrose after 2 h (B) of sucrose access. (C) However, the total amount of sucrose consumed per session was greater for rats using the IA2BC model compared to the DID model n = 8–12 per group. Unpaired T-tests with Holm-Sidak correction (alpha = 0.017). ####p < 0.0001 compared to IA2BC rats.
Figure 7
Figure 7
Comparison of weekly and hourly sucrose consumption using the IA2BC and DID models. (A) Using the IA2BC model (white), rats consumed more 5% sucrose per week compared to rats using the DID model (gray). (B) However, the average hourly sucrose intake was greater for DID rats compared to IA2BC rats. n = 8–12 per group. Unpaired two-tailed Student’s T-test. ****p < 0.0001.
Figure 8
Figure 8
Varenicline reduces sucrose consumption in DID rats following 30 min of sucrose access. (A) Administration of 2 mg/kg varenicline (gray) produced a significant reduction in sucrose consumption compared to saline (white) following 30 min of sucrose access using the DID model. Varenicline had no effect on sucrose consumption at the 2 h (B) and 4 h (C) time points n = 8 per group. Unpaired T-tests with Holm-Sidak correction (alpha = 0.017). ##p < 0.01 compared to vehicle.
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