Effects Of Continuous Operations And Sleep Deprivation On Cognitive Function In Human Brain And Mechanisms Of These Actions

In the modern society, more and more people have to face a long time continuous operation, even at the expense of natural sleep (ie, sleep deprivation) continuous operation, such as the continuous military operations, continuous vehicle driving. Working for long hours often leads to mental fatigue. There is evidence that mental fatigue is serious damage to cognitive function and behavior of the operator, and the metabolite of neuronal activity---adenosine inhibition of neuronal activity plays an important role during fatigue in the brain. Revealing the mechanism of continuous operation and sleep deprivation on cognitive function, will help combat the fatigue caused by continuous operation, continuous work and improve capacity of operators.In the present study, we firstly used a combined behavioral and functional magnetic resonance imaging (fMRI) design, allowing for a whole-brain, systems-level approach, to explore the ability of the human brain to form new digital memories in the absence of prior sleep. And then we investigated the electrophysiological effects of adenosine on stellate neurons in live brain slices of the EC using whole-cell patch-clamp recordings, observing the ionic and synaptic mechanisms involved in adenosine. The results show as follow: 1. Detrimental influence of continuous physical work and sleep deprivation on cognitive function in the human brainThe cognitive function of 30 continuous physical working people (3 days) and 6 sleep deprivation (SD) subjects (48h) were evaluated with Number cancellation test (NCT), Number searching test (NST) and Digit symbol substitution (DSST). The results of NCT showed that scores on accurate cancellation and total score had significant difference in the 1st and 3rd continuous physical work of people (n=30, P<0.05), and scores on false cancellation and error rate in 1st work (0.13±1.17/32.43±15.65%) was lower than that in 3rd continuous physical work (0.33±1.06/60.73±25.67%). NST also demonstrated that scores on total score in 1st work (6.6±3.83) was higher than 3rd continuous physical work (5.27±4.17), while scores on error rate on people in 1st work (37.54±25.90%) was significant lower than that in 3rd continuous physical work (48.91±30.40%) (n=30, P<0.05). NCT presented that after SD for 8h, the scores on both accurate cancellation and total score in SD subjects was lower than that in controls The same as SD for 16h, the scores on accurate cancellation and total score in SD subjects were 17.43±2.30 and 17.50±2.05, lower than that in controls (18.50±0.58/17.75±0.87). Experiment on DSST showed that the scores after SD for 8h, 32h and 48h decreased gradually, 24.67±1.51, 22.71±1.80 and 20.14±1.21, respectively. And the scores on SD for 16h and 40h were 23.43±7.93, 20.00±2.23, lower than that in controls (24.00±1.83/23.71±1.97). These results suggest that continuous physical work and sleep deprivation have an obvious detrimental influence on the cognitive function in human brain.2. Impairment of digital memory retrieval after 48h sleep deprivation6 subjects were awake during day 1, night 1, day 2 and night 2, accumulating approximately 48h of total sleep deprivation before the encoding session. Subjects underwent a digital memory encoding, maintenance and retrieval session during fMRI scanning in which they viewed a series of number (0 ~ 9). The results showed that the error rate (13.7±10.1) after SD was higher than that before SD (8.2±5.4), while the response time increased from 738.0±82.1 ms to 824.3±52.3ms after SD. During encoding trials different fMRI regions of significant activation (relative to fixation baseline) between sleep control and sleep deprivation are left Brodmann 30, left Brodmann 42, left Brodmann 41 and left Brodmann 6. During maintenance trials different fMRI regions of significant activation are left Brodmann 38, left Brodmann 21, left parahippocampus and amygdala, left Brodmann 47, left lentiform nucleus and thalamus, right lentiform nucleus, left Brodmann 30, right Brodmann 30, bilateral Brodmann 24 and bilateral Brodmann 6. During retrieval trials different fMRI regions of significantly negative activation are bilateral hippocampus, right amygdale, left precuneus, left thalamus. During retrieval trials different fMRI regions of significantly positive activation are left inferior frontal gyrus, left middle frontal gyrus, left middle temporal gyrus, bilateral cingulate gyrus, left inferior parietal lobule, Brodmann 21, Brodmann 24, Brodmann 47, Brodmann 19 and Brodmann 9.3. Inhibitory effects of adenosine on stellate neurons in EC 3.1 Adenosine inhibits Ih currents of stellate neuronsApplication of adenosine produced a reduction of voltage sag in recording neurons in response to hyperpolarizing current steps (from -350 to -150 pA, 50 pA, step), the voltage sag (peak voltage change-voltage change at steady state) decreased to 66±9% of control in the presence of adenosine (control, 13.0±5.9 mV; post-adenosine, 8.8±4.2 mV; n = 11; P < 0.001). In addition, adenosine produced a significant decrease in the amplitude of Ih currents evoked by the voltage step protocol (from -70 to -120 mV; -10 mV; step; 1000 ms). The suppression by adenosine on Ih currents was displayed in almost all hyperpolarized voltage steps except -70 mV. Together, these data indicate that adenosine inhibits the excitability of stellate neurons in the EC involved its inhibition on HCN channels.3.2 Adenosine activates presynaptic A1 receptors to decrease spontaneous glutamate release on to stellate neuronsIn the presence of bicuculline (10μM) and TTX (1μM) mEPSCs were recorded. Application of adenosine (100μM) significantly decreased the frequency (55±9 % of control; n = 16, p < 0.001), but not the amplitude (98±6 % of control; n = 16; p = 0.33) of mEPSCs. Application of adenosine A1 receptor antagonist DPCPX (3μM) completely blocked adenosine mediated decrease in mEPSCs frequency (n = 10; P = 0.35). The ability of adenosine A2 receptor antagonist DMPX (10μM) to block the effect of adenosine on mEPSCs was also tested. Application of adenosine A2 receptor antagonist DMPX (10μM) failed to change the adenosine-induced shift of the interevent interval distribution (n = 6; P < 0.001) excluding the involvement of adenosine A2 receptors. These results suggest that the adenosine-induced decrease in spontaneous glutamate release is mediated by presynaptic A1 receptors.3.3 Adenosine inhibits the GABAergic drive to stellate neurons by activating presynaptic A1 receptorsIn the presence of TTX (1μM), CNQX (10μM) and AP-V (50μM) mIPSCs were recorded. Application of adenosine (100μM) significantly decreased the frequency (51±6 % of control; n = 16, p < 0.001,), but not the amplitude (98±4 % of control; n = 16; p = 0.07) of mIPSCs. Application of adenosine A1 receptor antagonist DPCPX (3μM) completely blocked adenosine mediated decrease in mIPSCs frequency (n = 6; P = 0.47). Application of adenosine A2 receptor antagonist DMPX (10μM) failed to change the adenosine-induced shift of the interevent interval distribution (n = 10; P < 0.001) excluding the involvement of adenosine A2 receptors. These results suggest that the adenosine- induced decrease in spontaneous glutamate release is mediated by presynaptic A1 receptors.3.4 Inhibition of spontaneous glutamate and GABA release by adenosine A1 receptoractivation is mediated by voltage-dependent Ca2+ channels and extracellular Ca2+ Bath application of voltage-dependent Ca2+ channel (VDCC) blocker Cd2+ (100μM) alone significantly decreased the baseline frequency of both mEPSCs and mIPSCs in all of the neurons tested to 44±11% (n = 8; P < 0.001) and 56±11% (n = 7; P < 0.001; K-S test) of the control, respectively. After at least 5 min pretreatment of Cd2+, adenosine (100μM) failed to decrease mEPSC (n = 8; P = 0.30) and mIPSC frequency (n = 7; P = 0.20). Ca2+-free external solution also markedly decreased basal mEPSC and mIPSC frequency to 45±19% (n = 8; P < 0.001) and 51±15% (n = 9; P < 0.001) of the baseline, respectively. Furthermore, the application of 100μM adenosine did not produce a significant change in the frequency of mEPSCs (n = 8; P = 0.13) and mIPSCs (n = 9; P = 0.38) in the Ca2+-free solution. These results suggest that the adenosine A1 receptor-mediated inhibition of spontaneous glutamate and GABA release is related to the Ca2+ influx passing through presynaptic VDCCs.In summary, our study has indicated that continuous physical work and sleep deprivation have deleterious effect on human cognitive function, and digital memory retrieval was impaired after 48 sleep deprivation. Adenosine inhibits the excitability of stellate neurons in the EC through inhibition on HCN channels. In addition, adenosine-induced decrease in spontaneous glutamate and GABA release is mediated by presynaptic A1 receptors. Furthermore, adenosine A1 receptor-mediated inhibition of spontaneous glutamate and GABA release is related to the Ca2+ influx passing through presynaptic VDCCs.