Suppression of hippocampal plasticity-related gene expression by sleep deprivation in rats

Abstract

Previous work shows that sleep deprivation impairs hippocampal-dependent learning and long-term potentiation (LTP). Brain-derived neurotrophic factor (BDNF), cAMP response-element-binding (CREB) and calcium-calmodulin-dependent protein kinase II (CAMKII) are critical modulators of hippocampal-dependent learning and LTP. In the present study we compared the effects of short- (8 h) and intermediate-term (48 h) sleep deprivation (SD) on the expression of BDNF and its downstream targets, Synapsin I, CREB and CAMKII in the neocortex and the hippocampus. Rats were sleep deprived using an intermittent treadmill system which equated total movement in the SD and control treadmill animals (CT), but permitted sustained periods of rest in CT animals. Animals were divided into SD (treadmill schedule: 3 s on/12 s off) and two treadmill control groups, CT1 (15 min on/60 min off) and CT2 (30 min on/120 min off - permitting more sustained sleep). Real-time Taqman RT-PCR was used to measure changes in mRNA; BDNF protein levels were determined using ELISA. In the hippocampus, 8 h treatments reduced BDNF, Synapsin I, CREB and CAMKII gene expression in both SD and control groups. Following 48 h of experimental procedures, the expression of all these four molecular markers of plasticity was reduced in SD and CT1 groups compared to the CT2 and cage control groups. In the hippocampus, BDNF protein levels after 8 h and 48 h treatments paralleled the changes in mRNA. In neocortex, neither 8 h nor 48 h SD or control treatments had significant effects on BDNF, Synapsin I and CAMKII mRNA levels. Stepwise regression analysis suggested that loss of REM sleep underlies the effects of SD on hippocampal BDNF, Synapsin I and CREB mRNA levels, whereas loss of NREM sleep underlies the effects on CAMKII mRNA.

Figure 1. Effects of 8 h and 48 h of SD on the expression of BDNF (A and C) and its protein (B and D) determined by Taqman RT-PCR and ELISA in the hippocampus

Each value is expressed as a percentage of the cage control value (100%), and represents the mean ±s.e.m. of the group of eight animals. CC, cage control group; SD, sleep deprivation; CT1, control treadmill 1 (15 min on/60 min off); CT2, control treadmill 2 (30 min on/120 off). *P < 0.05, **P < 0.01, One-way ANOVA followed by Bonferroni's post hoc test.

Figure 2. Effects of 8 h and 48 h of SD on mRNA expression of Synapsin I (A and D), CREB (B and E) and CAMKII (C and F) in the hippocampus

Data are presented as percent of the cage control (CC) group. SD, sleep deprivation; CT1, control treadmill 1 (15 min on/60 min off); CT2, control treadmill 2 (30 min on/120 min off). Note that the CT2 group has comparable values to those of the CC. n = 8, *P < 0.05, **P < 0.01, one-way ANOVA followed by Bonferroni's post hoc test.

Figure 3. Effects of 8 h and 48 h of SD on the expression of BDNF (A and D), Synapsin I (B and E) and CAMKII (C) mRNA as determined by Taqman RT-PCR in the neocortex from the same group of animals used for measurements of these transcripts in the hippocampus

Each value is expressed as a percentage of the cage control value (100%), and represents the mean ±s.e.m. for a group of eight animals.

Figure 4. Correlations between sleep–wake cycle parameters and BDNF and Synapsin 1 mRNA levels

A–E, across all the experiments in the 48 h group, BDNF mRNA levels in the hippocampus correlate negatively with the percentage of time spent in waking (r =−0.45; P < 0.01; A) and positively with the percentages of NREM (r = 41; P < 0.05; B), REM (r = 0.53; P < 0.01, C), total sleep (r = 0.45; P < 0.01, D) and the NREM sleep bout duration (r = 0.61; P < 0.001, E). F–J, correlations between sleep–wake cycle parameters and Synapsin I mRNA levels. Synapsin I mRNA levels in the hippocampus correlated negatively with the percentage of time spent in waking (r =−0.52; P < 0.01, F), and positively with the percentages of NREM (r = 0.44; P < 0.01, G), REM (r = 0.77; P < 0.001, H), total sleep (r = 0.52; P < 0.01, I) and the number of REM sleep bouts (r = 0.62; P < 0.001, J).

Figure 5. Correlations between sleep–wake cycle parameters and CREB and CAMKII mRNA levels

A–D, CREB mRNA levels correlated positively with the NREM length bout (r = 0.41; P < 0.05, A), the number of REM sleep bouts (r = 0.4; P < 0.05, B), the REM sleep bout duration (r = 0.4; P < 0.05, C) and the percentage of REM sleep (r = 0.55; P < 0.001, D). E–I, correlations between sleep–wake cycle parameters and CAMKII mRNA levels. CAMKII mRNA levels showed a negative correlation with the percentage of waking (r =−0.42; P < 0.05, E) and a positive correlation with the percentage of time spent in NREM sleep (r = 0.4; P < 0.05, F), REM sleep (r = 0.45; P < 0.01, G), total sleep (r = 0.42; P < 0.05, H) and the NREM bout length (r = 0.41; P < 0.05, I).