Effects of chronic caffeine consumption on sleep and the sleep electroencephalogram in mice

Abstract

Background: Caffeine is one of the most widely consumed psychostimulants, and it impacts sleep and circadian physiology.

Aim: Caffeine is generally used chronically on a daily basis. Therefore, in the current study, we investigated the chronic effect of caffeine on sleep in mice.

Methods: We recorded the electroencephalogram and electromyogram on a control day, on the first day of caffeine consumption (acute), and following two weeks of continuous caffeine consumption (chronic). In the latter condition, a period of six-hour sleep deprivation was conducted during the light period. Control mice, which received normal drinking water, were also recorded and sleep deprived.

Results: We found that caffeine induced differential effects following acute and chronic consumption. Over 24 h, waking increased following acute caffeine whereas no changes were found in the chronic condition. The daily amplitude of sleep-wake states increased in both acute and chronic conditions, with the highest amplitude in the chronic condition, showing an increase in sleep during the light and an increase in waking during the dark. Furthermore, electroencephalogram slow-wave-activity in non-rapid eye-movement sleep was increased, compared with both control conditions, during the first half of the light period in the chronic condition. It was particularly challenging to keep the animals awake during the sleep deprivation period under chronic caffeine.

Conclusions: Together the data suggest an increased sleep pressure under chronic caffeine. In contrast to the traditional conception on the impact on sleep, chronic caffeine intake seems to increase the daily sleep-wake cycle amplitude and increase sleep pressure in mice.

Keywords: Caffeine; electroencephalogram; mice; sleep.

Figure 1.

(a) A representative example of locomotor activity (passive infrared (PIR) recording) of the activity of a mouse. During the first 13 days the mouse drank exclusively caffeinated water (indicated by the black bar on the left). Subsequently, the bottle was replaced with normal drinking water. Black and white bars at the top indicate the light–dark cycle. (b) Average time course of locomotor activity over the last 10 days of chronic caffeine treatment and the first 10 days after return to normal water (n=7). Curves connect one-hour values (mean±standard error of the mean (SEM)) of locomotor activity recorded with a passive infrared sensor. The black and white bars indicate the light–dark cycle. Asterisks indicate significant differences between the two conditions (p<0.05 paired t-test, after significant two-way analysis of variance (ANOVA), factors ‘treatment’בtime of day’)

Figure 2.

(a) Dark, light and 24-hour values of sleep–wake states (n=7). Note that the light and dark data for the chronic caffeine condition are plotted in reverse order of recording to match the order of recording of the control and acute condition. Asterisks indicate significant differences between conditions (post-hoc Tukey’s multiple comparisons test after significant two-way repeated analysis of variance (r-ANOVA), factors ‘treatment’בlight–dark’ or one-way r-ANOVA factor ‘treatment’ (24-hour values). (b) Light–dark amplitude of sleep–wake states. Asterisks indicate significant differences between conditions (p<0.05, post-hoc Tukey’s multiple comparisons test after significant one-way r-ANOVA factor ‘treatment’). NREM: non-rapid eye movement; REM: rapid eye movement.

Figure 3.

Time course of waking, non-rapid eye movement (NREM) sleep, rapid eye movement (REM) sleep, and electroencephalogram (EEG) slow-wave-activity (SWA) in NREM sleep for the 24-hour baseline day in the control condition and during the acute and chronic caffeine conditions (n=7). Note that the light and dark data for the chronic caffeine condition are plotted in reverse order of recording to match the order of recording of the control and acute condition. Curves connect two-hour values (mean±standard error of the mean (SEM)). The black and white bars indicate the light–dark cycle. Asterisks indicate significant differences between acute (grey) or chronic (black) caffeine condition compared with control. The circles indicate significant difference between the acute and chronic caffeine condition (p<0.05, Bonferroni multiple comparisons test after significant two-way ANOVA, factors ‘treatment’ or ‘treatment’בtime of day’).

Figure 4.

Electroencephalogram (EEG) power density in waking, non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. Between 0.25 and 5.0 Hz, values were calculated in 0.5-Hz bins and between 5.25 and 25.0 Hz in 1-Hz bins (n=7). Values are plotted at the upper limit of each bin. Curves connect 24-hour mean values of relative power density for the acute and chronic caffeine condition relative to the control condition (=100%). Thick lines above the curves indicate frequencies where the chronic caffeine (black) and acute caffeine (grey) conditions differ from control. Differences between the acute and chronic condition are indicated by thin black lines (p<0.05, Tukey’s multiple comparisons tests after significant two-way repeated analysis of variance (r-ANOVA), factors ‘treatment’בEEG-frequency’).

Figure 5.

Time course of sleep–wake states and electroencephalogram (EEG) slow-wave-activity (SWA) in non-rapid eye movement (NREM) sleep, for 24 h baseline, six-hour sleep deprivation (SD, hatched area) and 18 h recovery for the second control group (n=11) and the chronic caffeine group (n=7). Curves connect two-hour values (mean±standard error of the mean (SEM)) of waking, NREM sleep, rapid eye movement (REM) sleep and EEG SWA. The black and white bars indicate the light–dark cycle. Asterisks and asterisks with lines indicate significant differences between the two groups. Significant effects of SD are indicated by open (control) and closed (chronic caffeine) circles (p<0.05, Bonferroni multiple comparisons test after three-way analysis of variance (ANOVA), factors ‘treatment’בtime of day’בday’ with significant interactions ‘treatment’בtime of day’ for waking, NREM and REM sleep and ‘treatment’בday’ for EEG SWA).