[Effects of noise, bright light and mechanical stimulation on sleep, blood-brain barrier and cognitive function in...

To evaluate the effects of noise, bright light and mechanical stimulation on sleep, blood-brain barrier and cognitive function in septic rats.

Forty male Sprague-Dawley (SD) rats were selected and intraperitoneal injection of 10 mg/kg lipopolysaccharide (LPS) was used to establish sepsis model. 0, 30, 45, 60, 75 dB noise stimulation or 0, 50, 100, 200, 400 Lux light stimulation were given to rats (all n = 4). The serum levels of cortisol and melatonin, and the cerebral content of Evans blue (EB) were measured 96 hours after the stimulation to determine the optimal intensity of intervention. The other 40 SD rats were randomly divided into control group (Con group), LPS group, noise intervention group (LPS+60 dB group), 200 Lux light intervention group (LPS+200 Lux group) and mechanical stimulation group (LPS+MS group), with 8 rats in each group. The open fields test and fear conditioning test were used to evaluate the exploratory behavior and cognitive function 96 hours after corresponding stimulation. The enzyme linked immunosorbent assay (ELISA) was used to detect cerebral level of interleukin-6 (IL-6) and serum levels of cortisol and melatonin. The blood-brain barrier integrity was assessed by EB staining. The protein levels of ZO-1, Claudin-5 and caspase-3 in the hippocampus were detected by Western blotting to assess the blood-brain barrier integrity and neuronal apoptosis.

Compared with 0 dB group or 0 Lux group, the serum melatonin concentration in 60 dB group and 200 Lux group were significantly reduced, while the serum cortisol concentration and cerebral EB content were significantly increased. Therefore, 60 dB noise and 200 Lux light were selected in the subsequent experiments. Compared with Con group, the horizontal score and vertical score in the open field test in LPS group were significantly decreased. There were no significant differences in the proportion of freezing time, the cerebral contents of EB and IL-6, the serum levels of melatonin and cortisol, and the hippocampal expressions of ZO-1, Claudin-5 and caspase-3. Compared with LPS group, the horizontal score, vertical score and the percentage of freezing time in LPS+60 dB group, LPS+200 Lux group and LPS+MS group were significantly reduced [horizontal score: 73.8±9.7, 80.3±9.4, 64.5±8.3 vs. 103.6±15.5; vertical score: 9.4±1.7, 11.2±1.9, 6.8±0.9 vs. 15.9±2.8; the percentage of freezing time: (45.3±4.7)%, (53.3±5.8)%, (42.1±5.1)% vs. (66.1±6.3)%], the serum level of melatonin was significantly decreased (ng/L: 53.62±6.20, 44.25±6.41, 45.33±5.84 vs. 74.39±7.54), the serum level of cortisol was significantly increased (nmol/L: 818.34±95.53, 710.04±65.41, 989.73±91.63 vs. 398.82±72.59), the levels of EB, IL-6 in the brain tissue were significantly increased [EB (μg/g): 2.80±0.35, 2.38±0.31, 3.24±0.42 vs. 1.59±0.26; IL-6 (ng/g): 31.56±4.11, 26.69±3.75, 37.47±4.56 vs. 16.28±2.69], the expressions of ZO-1 and Claudin-5 were significantly decreased (ZO-1/β-actin: 0.37±0.04, 0.32±0.05, 0.24±0.04 vs. 0.80±0.09; Claudin-5/β-actin: 0.62±0.08, 0.47±0.06, 0.35±0.05 vs. 0.97±0.20), and the expression of cleaved caspase-3 was significantly increased (caspase-3/β-actin: 0.56±0.06, 0.39±0.04, 0.72±0.12 vs. 0.20±0.03), with statistically significant differences (all P < 0.05).

60 dB noise, 200 Lux light or mechanical stimulation for 96 hours could inhibit the secretion of serum melatonin, promote the secretion of cortisol, and activate neuroinflammation in septic rats, and lead to neuronal apoptosis in hippocampus and hyper-permeability of blood-brain barrier, which in turn could cause sleep disturbance and cognitive impairment.