Effects of withdrawal from chronic intermittent ethanol vapor on the level and circadian periodicity of running-wheel activity in C57BL/6J and C3H/HeJ mice

Abstract

Background: Alcohol withdrawal is associated with behavioral and chronobiological disturbances that may persist during protracted abstinence. We previously reported that C57BL/6J (B6) mice show marked but temporary reductions in running-wheel activity, and normal free-running circadian rhythms, following a 4-day chronic intermittent ethanol (CIE) vapor exposure (16 hours of ethanol vapor exposure alternating with 8 hours of withdrawal). In the present experiments, we extend these observations in 2 ways: (i) by examining post-CIE locomotor activity in C3H/HeJ (C3H) mice, an inbred strain characterized by high sensitivity to ethanol withdrawal, and (ii) by directly comparing the responses of B6 and C3H mice to a longer-duration CIE protocol.

Methods: In Experiment 1, C3H mice were exposed to the same 4-day CIE protocol used in our previous study with B6 mice (referred to here as the 1-cycle CIE protocol). In Experiment 2, C3H and B6 mice were exposed to 3 successive 4-day CIE cycles, each separated by 2 days of withdrawal (the 3-cycle CIE protocol). Running-wheel activity was monitored prior to and following CIE, and post-CIE activity was recorded in constant darkness to allow assessment of free-running circadian period and phase.

Results: C3H mice displayed pronounced reductions in running-wheel activity that persisted for the duration of the recording period (up to 30 days) following both 1-cycle (Experiment 1) and 3-cycle (Experiment 2) CIE protocols. In contrast, B6 mice showed reductions in locomotor activity that persisted for about 1 week following the 3-cycle CIE protocol, similar to the results of our previous study using a 1-cycle protocol in this strain. Additionally, C3H mice showed significant shortening of free-running period following the 3-cycle, but not the 1-cycle, CIE protocol, while B6 mice showed normal free-running rhythms.

Conclusions: These results reveal genetic differences in the persistence of ethanol withdrawal-induced hypo-locomotion. In addition, chronobiological alterations during extended abstinence may depend on both genetic susceptibility and an extended prior withdrawal history. The present data establish a novel experimental model for long-term behavioral and circadian disruptions associated with ethanol withdrawal.

Fig. 1

Standard raster-style circadian actograms (double-plotted) of wheel-running (left) and water-tube licking activity (right) of representative individual C3H mice exposed to 1-cycle control (CONT) and CIE treatments (top and bottom panels, respectively). Arrows indicate beginning and end of treatment protocols. Shaded region denotes lights off. Note that wheel-running was recorded during treatment but that licking was not.

Fig. 2

Standard raster-style circadian actograms (double-plotted) of representative B6 and C3H mice exposed to 3-cycle control (CONT; top) and CIE (bottom) treatments. Arrows indicate beginning and end of treatment protocols. Shaded region denotes lights off. Note that wheel-running activity was not recorded during treatment.

Fig. 3

Mean (±SEM) wheel-running (left) and water-tube licking (right), plotted relative to baseline levels (see text), following 1-cycle control and CIE treatments in C3H mice (Experiment 1). Dotted lines represent 100% baseline activity level. Asterisks (*, P < 0.05; **, P < 0.01) indicate days on which significant group differences were detected by Bonferroni-protected post-hoc tests.

Fig. 4

Mean (±SEM) levels of wheel-running activity plotted relative to baseline levels following 3-cycle control and CIE treatments in B6 (left) and C3H (right) mice. Other conventions as in Fig. 3.

Fig. 5

Mean (±SEM) free-running circadian period and initial phase in constant darkness (DD) following CIE protocols in B6 and C3H mice. Asterisks (***) indicate significant difference between CIE and CONT mice (P < 0.0001).