Remarks on the effects of limiting fluid access and modifying environments on fluid consumption
The purpose of the first phase of the experiment was to assess the effect of changing environments on ethanol drinking behaviors. Use of the Automated Wheel Monitor (AWM) system created a more complex, enhanced housing condition; therefore, we measured ethanol drinking over three changing conditions (1) standard housing, (2) enhanced AWM cage with a blocked wheel, and (3) enhanced AWM cage with wheel access. During the Standard period mice were subjected to standard individual housing conditions for the two bottle choice ethanol preference test where they consumed 10.8 ± 0.7 g/kg/24 hours pure ethanol and 74 ± 11 g/kg/24 hours water with an ethanol preference ratio of 0.66 ± 0.05. During the Baseline 1 period, fluids were accessible only during lights off (3:00 PM to 3:00 AM) and mice were subjected to enhanced environment housing conditions with a mechanically blocked wheel. Changing the environment and restricting fluid access resulted in 6.4 ± 0.6 g/kg/12 hours pure ethanol consumption and a water consumption of 97 ± 12 g/kg/12 hours, with an ethanol preference ratio of 0.47 ± 0.05. Unblocking the wheel, thus allowing access to wheel running (Wheel 1 period) did not produce a change in 10% ethanol solution consumption (67 ± 14 g/kg/12 hours, with 5.4 ± 0.6 g/kg/12 hours pure ethanol), but did increase water consumption (118 ± 10 g/kg/12 hours) without a change in total fluid consumption [Baseline 1 vs. Wheel 1 comparison, paired Student’s t-test; water consumption, P <.01] (). Accompanying these results was a significant decrease in ethanol preference ratio (0.37 ± 0.04) [Baseline 1 vs. Wheel 1 comparison, paired Student’s t-test; ethanol preference, P <.05].
Figure 1 Voluntary fluid consumption. (A) 10% ethanol preference is presented as a ratio of the amount of ethanol solution consumed divided by total fluid consumption. (B) Ethanol consumption (g/kg/12 hr). (C) Water consumption (g/kg/12 hr). (D) Total fluid consumption (more ...)
Alternating periods of wheel access modifies ethanol drinking patterns but not wheel running
During the second phase of the experiment, mice were subjected to six alternating periods in which the running wheel was blocked (Baseline 1, 2, and 3) or accessible (Wheel 1, 2, and 3) to assess the effects of wheel running on ethanol-related behaviors. We hypothesized that wheel access would not change ethanol preference or consumption, but would compress normal drinking patterns, resulting in fewer ethanol bouts and a greater amount of ethanol consumed per bout. Data for ethanol preference, ethanol consumption, water consumption, and total fluid consumption from each period are presented in , while ethanol-related behaviors characterizing patterns of drinking from each period are presented in .
Ethanol-related behavioral data
Wheel access had no significant effect on ethanol consumption, ethanol preference or total fluid consumption, but wheel access changed ethanol drinking patterns. Wheel access resulted in an increased number of ethanol bouts [main effect of wheel access - F(1,13) = 5.28, P <.05], an increased time spent drinking ethanol [main effect of wheel access - F(1,13) = 4.65, P <.05], and a decreased amount of ethanol consumed per bout [main effect of wheel access - F(1,13) = 4.81, P <.05, P <.05; ].
Changes in drinking patterns due to wheel access can be summarized as an increased number of ethanol bouts, time spent drinking ethanol, and a reduced amount of ethanol consumed per bout. Alternating periods of wheel access (periods Wheel 1, 2, and 3) in the presence of ethanol did not significantly change subsequent wheel running distance, time spent running, or average RPM ( and ).
Figure 2 Average distance travelled on the running wheel. (A) Wheel running distance (km/12 hours) data for each period. **-P <.01 (paired Student’s t-test). (B) Wheel running distance (km/12 hours) data for individual mice for Wheel 3, Wheel 4, (more ...)
Measurement of wheel activity
Effect of alternating ethanol availability on wheel running and ethanol consumption
The third phase of the experiment began with period Wheel 3, followed by a fourth wheel access period in which ethanol was not offered (Wheel 4) and a fifth wheel access period where ethanol was again offered (Wheel 5). Forced ethanol abstinence resulted in increased wheel running time and distance, and this effect was reversed upon the reintroduction of ethanol (). We measured distance traveled, time spent running, and average wheel RPM when running as wheel activity parameters ( and ). In the third phase of the experiment, mice ran 6.9 ± 0.6 km/day during period Wheel 4 (in the absence of ethanol), a significantly greater distance than during Wheel 3 (in the presence of ethanol), where mice ran a distance of 6.3 ± 0.5 km/12 hours [paired Student’s t-test, P <.01]. This distance decreased to 5.4 ± 0.6 km/12 hours during Wheel 5, when ethanol was reintroduced [paired Student’s t-test, P <.01]. In addition to running distance, the amount of time spent running varied with ethanol accessibility. The amount of time spent running was significantly decreased from 363 ± 16 minutes during Wheel 4 to 282 ± 19 minutes during Wheel 5, when ethanol was reintroduced [paired Student’s t-test, P <.0001]. The average wheel RPM was not significantly changed by ethanol deprivation [paired Student’s t-test to compare Wheel 3 and 4, P >.05; paired Student’s t-test to compare Wheel 4 and 5, P >.05].
Wheel running in the absence of ethanol resulted in an increase in alcohol consumption, suggesting an ethanol deprivation effect (, ). In addition to ethanol consumption, ethanol preference and the time spent drinking ethanol were increased in Wheel 5 as compared with Wheel 3 [paired Student’s t-tests - ethanol consumption, P <.05; ethanol preference, P <.01; time spent drinking ethanol]. There were no observed changes in total fluid consumption, number of ethanol bouts, or amount of ethanol consumed per bout.
Ethanol deprivation effect: Individual means for Wheel 3 and Wheel 5 periods. (A) 10% ethanol preference is presented as a ratio of the amount of ethanol consumed divided by total fluid consumption. (B) Ethanol consumption (g/kg/12 hr).