Effects of Gz and noise combined stress on learning and memory function in rats

Effects of Gz and noise combined stress on learning and memory function in rats

【Abstract】 Objective : To investigate the effects of moderate-intensity positive acceleration and noise on the learning and memory function of rats. Methods : 32 male Sprague-Dawley rats were randomly divided into control group, + 6 GzP3 min group, 90 dB(A)P30. Min noise group, + 6 GzP3 min and 90 dB(A)P30 min noise combined stress group 4, each group of 8. Using Y2 maze test and darkness test to observe the learning and memory function of rats at different times after stress Changes. Results : The correct rate of rats in the Gz group was significantly lower than that in the control group at 2, 4 and 6 days after exposure ( P < 0.01), and the response time was significantly prolonged ( P < 0.01). rat accuracy upon exposure each time point compared with the control group and the noise group were significantly lower (P <0. 01), were significantly longer (P <0.01) during the reaction, it was + Gz group was no significant change; total time and the number of errors increases significantly immediately after exposure compared with the control group (P <0. 01), the incubation period immediately after exposure significantly reduced (P <0. 05), at 6 d post-exposure remained significantly shortened (P <0. 05 Conclusion : + 6 GzP3 min and 90 dB(A)P30 min noise combined stress can cause persistent learning and memory dysfunction in rats.

Key words: stress; positive acceleration; noise; learning and memory; rat

0 Introduction

The special working environment of military flight makes the pilot pilots inevitably exposed to various stressors. Two of the more common aviation stressors are positive acceleration (+Gz) and noise, which have become important factors threatening flight safety. Therefore, it is of great practical significance to explore the effect of compound stress on the working ability of flight personnel and its mechanism. Our previous research work shows that high G (+ 10 GzP3 min) and 90dB (A) P30 min noise combined stress can be It causes persistent learning and memory dysfunction in rats, with high G as the main influencing factor [1]. However, during actual flight, fighter pilots can partially avoid excessively high G by adjusting their flight actions and attitudes. The value is generated, so it is usually exposed to moderate acceleration (around + 6 Gz). However, there is little report on the effect of + Gz and noise on the learning and memory function of rats with moderate G value. We aimed to investigate the changes of learning and memory function in rats after + 6 GzP3 min and 90 dB (A)P30 min noise combined stress.

1 Materials and methods

1.1 Materials 32 male SD rats, body weight (165 ± 10) g. 1 wk prior to the experiment before feeding in experimental environment, the experimental environment to adapt to exclude shock, environmental factors such as learning and memory in rats The rats were randomly divided into control group, noise group, + Gz group and compound stress group, with 8 rats in each group.

1. 2 methods

1. 2. 1 Acceleration and noise action mode The animal centrifuge is used for + Gz exposure. The radius of the animal centrifuge is 2 m, and the simulated positive acceleration range is + 1~ + 12 Gz. The acceleration program is controlled by computer. The self-made plexiglass box (volume 15 cm × 5 cm × 3 cm) carries the rat and is horizontally fixed on the arm of the centrifuge. The rat head is oriented toward the axis of rotation of the centrifuge. The noise is generated by the UZ23 white noise generator. (Beijing Great Wall Radio Factory) produced. + Gz group rats had a G value of + 6 Gz, a peak action time of 3 min, and an acceleration rate of 1 GPs. The noise exposure level of the noise group was 90 dB(A). The frequency is 1000 Hz and the action time is 30 min. The noise action condition of the rats in the compound stress group is the same as that of the noise group. The composite + 6 Gz exposure is 3 min from the 27th minute of noise action, and the acceleration condition is the same as that of the +Gz group. Rats were placed only in plexiglass boxes for 3 min without + Gz and noise exposure. 1. 2. 2 Y2 labyrinth experiment Y2 labyrinth is a three-part radiant labyrinth box consisting of three arms and one connecting zone The three arms are at an angle of 120° to each other, each arm is 40 cm long and 15 c wide. m, the bottom is covered with a copper rod with a diameter of 5mm and a spacing of 6 mm [2]. The end of each arm is equipped with a signal light, and the signal light is turned on to indicate that the arm is a safe zone, that is, the bottom of the arm is not energized. The orientation of the safety zone is in accordance with A → C → B transformation, when one arm is a safe zone, the other two arms and the connection zone have stimulation voltage. The experiment is carried out in a quiet, dimly lit environment. At the beginning of the experiment, the rat is placed in the B arm of the maze. In the middle, make it adapt to the environment for 1 min, then power on, A light is on. After 5 s delay, the two arms and the connection area that are not lit start to be energized, and the electric shock voltage is 40 V. At this time, the light still lasts for 60 s, then Turn off the light, that is, complete a test. Perform 15 tests per experiment to record the correct rate and reaction time of the rats. The reaction time is the time taken for the safety arm to light up until the rat reaches the safety arm. Record the different stress immediately, 2, 4 and 6 d results.

1. 2. 3 The darkness test experiment box consists of two boxes, light and dark. The bottom of the box is covered with copper mesh, and the black box is connected with 40 V AC. The center of the wall connected to the black box has a hole, and the rat can pass freely [3 First, the rat was placed in a clear box. Due to its drilling and blackening nature, the rat was drilled into the black box, and the rat escaped to the light box due to electric shock. This is a learning. The residence time in the box was more than 5 min for the study. The total time, latency and number of errors used by the rats to learn immediately after stress and 6 days were recorded.

All experimental time is from 8:00 am to 12:00 pm daily, under the same environment and similar conditions.

Statistical processing: All data are expressed as x ± s, using SPSS

10. 0 for windows The repeated measurement variance analysis was performed on the Y2 labyrinth experiment results, and the non-parametric rank sum test was performed on the results of the darkness test.

2 results

2. 1 Correct rate and change in response + The correct rate of rats in the Gz group was significantly lower than that of the control group at 2, 4 and 6 days after exposure (P <

0. 01), the rats in the noise group were significantly lower than the control group immediately after exposure (P < 0.05). The rats in the composite stress group were significantly lower than the control group and the noise group at each time point after exposure (P < 0. 01), and there was no significant difference compared with the + Gz group (Fig 1).

Figure 1 Changes in the correct rate of rats after combined stress

The rats in the Gz group were significantly longer than the control group at 2, 4, and 6 days after exposure (P < 0.01), while the noise group did not change significantly at each time point after exposure. The rats in the compound stress group showed significant delay at each time point after exposure compared with the control group and the noise group.

Long (P < 0.01), and there was no significant difference compared with the + Gz group (Fig 2).

Fig 2 Changes of reaction time after combined stress ( n = 8 , x ± s )

Figure 2 Changes in rats after compound stress

2.2 total time latency variations and the number of errors immediately after exposure, total time + Gz group of rats and noise, latency and the number of errors than the control group were not significantly different, whereas the control rats, total composite The time and error number increased significantly (P < 0.01), and the latency was significantly shortened (P < 0.05). At 6 days after exposure, the latency of the + Gz group and the composite stress group was significantly shorter than that of the control group. ( P < 0.05, Tab 1).

Table 1 Changes in total time, latency, and number of errors in rats after stress

Tab 1 Changes of total time (TT) , latent time (LT) and number of error (NE) in rats after stress ( n = 8 , x ± s)

Group 0 d 6 d

TT(s) LT(s) NE LT(s)

Contro l 396. 5 ±110. 5 21. 6 ±20. 7 2. 0 ±1. 1 35. 4 ±20. 2

Noise 387. 0 ±98. 4 21. 7 ±14. 8 2. 1 ±1. 5 32. 3 ±23. 8

+ Gz 448. 9 ±93. 6 42. 4 ±18. 1 1. 3 ±0. 7 1. 9 ±1. 0 ^a

Combined 563. 0 ±109. 6 ^b 4. 9 ±2. 6 ^{a     Â}  7. 4 ±4. 8 ^b 2. 0 ±1. 3 ^a

^a P < 0.05, ^b P < 0. 01 vs control .

3 discussion

With the equipment of a new generation of high-performance fighters, pilots have been exposed to a variety of undesirable aviation stress factors more frequently than ever before. The most common and most harmful ones are positive acceleration and noise. The adverse effects of personnel's intelligence level and work ability have gradually attracted the attention of aviation medical workers. In this study, we used the Y2 maze, darkness test and other behavioral experimental methods to observe the medium-intensity positive acceleration and noise after compound stress. Changes in learning and memory function in rats, found that + 6 GzP3 min and 90dB (A) P30 min noise combined stress can cause persistent learning and memory dysfunction in rats. The influence of positive acceleration on brain has been widely concerned by scholars at home and abroad. A lot of experimental work was carried out on the pathological changes of brain tissue after high G value exposure. The changes of brain tissue morphology after high G value were observed, and the nature, time course and mechanism of brain injury caused by high G exposure were systematically revealed [4, 5 On this basis, the influence of positive acceleration on brain function is further explored [1,6]. Wei Yingbo et al. [6] used Y2 maze and market analysis. Behavioral test methods such as dark-avoidance experiments were performed to observe the changes in memory function and behavior of rats after + Gz exposure with different intensities and durations. It was found that + 10 GzP3 min exposure can cause transient memory retention in rats. Obstacles, but there was no significant change in memory function of rats after + 6 GzP3 min exposure. The results of this experiment showed that the correct rate of rats in the +6 GzP3 min group was significantly decreased at 2, 4 and 6 days after exposure, and the reaction time was significantly prolonged. , indicating that + 6 GzP3 min exposure can cause a decrease in learning function persistence in rats. The above results suggest that although learning function and memory function are closely related to two brain functions, after + Gz exposure, learning and memory are both functions. There may be some differences in the changes. The change of learning ability may be more sensitive to the changes of ischemia and hypoxia than the memory function, that is, the learning function is more susceptible to + Gz exposure. The reason may be due to the need to reach the level of learning in the learning process. Long-term memory, while long-term memory requires the synthesis of new protein molecules, which may be related to certain permanent functional and structural changes in the brain, + Gz exposure Cerebral ischemia and hypoxia changes inhibit the normal activities of rat nerve cells, which may hinder the transformation of short-term memory into long-term memory, which is manifested as a decline in learning ability in rats. The corresponding long-term memory has been formed, that is, some structural changes have taken place in the brain-related brain regions, so the memory ability of the rats is better maintained after the +Gz exposure.

The influence of noise exposure on people's work ability has always been one of the important research topics in public health medicine and occupational medicine. Domestic and foreign scholars have used a variety of behavioral experimental methods to study human and animal learning under different noise exposure intensity and exposure time. Changes in memory function, found that 80 ~ 96 dB of noise exposure for 30 min can cause learning and memory dysfunction in humans and animals [7,8]. Most scholars believe that noise mainly affects learning energy

Force and short-term memory, but no effect or influence on long-term memory. The results of this experiment show that the correct rate of the noise group rats is only significantly reduced immediately after exposure, and has basically recovered 2 days after exposure, suggesting 90 dB. (A) 30 min of noise exposure can cause transient learning and memory impairment in rats. The experimental results are consistent with previous reports [7,8]. The mechanism may be that under the action of noise, noise information is projected to the cerebral cortex. The area, and beyond its normal level of excitement, so that the pain information caused by the electric shock cannot or weaken the temporary association with the cortex that controls the avoidance response, resulting in reduced animal learning ability [9]. The fighter pilot is often exposed to the flight. There are many adverse environmental factors such as positive acceleration and noise, but the effects of positive acceleration and noise on the learning and memory have rarely been reported. The results of this experiment show that the rats in the positive acceleration and noise combined stress group are exposed after exposure. The correct rate of time was significantly reduced, the reaction time was significantly prolonged, the total time and number of errors increased significantly, and the latency was significantly shortened, suggesting that + 6 GzP30 min and 90 dB(A)P30 min Combined stress can cause severe persistent learning and memory dysfunction in rats. Under the simultaneous action of positive acceleration and noise, the two stress factors have certain synergistic effects, and the composite stress learns from rats compared with simple positive acceleration or noise. The influence of memory function has a certain degree of enhancement in the extent and duration of damage.