ã€Abstract】 Objective To investigate the effects of psychological stress on working memory (memorymemory) and the intervention of tyrosine, a precursor of the central transmitter dopamine (DA) . The method first with eight-arm radial maze training in rats (1 / d, 6d / week for 10 weeks) to learning and memory are formed, and then to CommunicationBox model rats were continuously 14d, 30min / d psychological stress, and from from administered 0d via feed 250, 500 and 1000mg / kg3 doses of tyrosine intervention, observation, 4, 7, 10, 13 days of working memory errors (workingmemoryerror) and reference memory errors (referencememoryerror). Results Compared with the control group , the working memory errors of the psychological stress group on days 1 , 7, 10, and 13 and the reference memory errors measured at all times were higher than those of the control group. Compared with the psychological stress group , the tyrosine 1000 mg/kg group showed a decrease in working memory error on the 7th and 13th day , and the reference memory error decreased on the 4th and 10th day , the tyrosine 500mg/kg group On the 10th day, there was also a decrease in working memory errors and reference memory errors , and no significant statistically significant changes were observed in the tyrosine 250 mg/kg group. Conclusion Acute and repetitive psychological stress can impair the work of rats
Memory , high-dose tyrosine can reduce the damage of working stress in working memory at an early stage . 500mg/kg tyrosine intervention also has a certain effect on reducing working memory damage caused by long-term psychological stress.
ã€Key words】 Psychological stress ; Working memory ; Tyrosine
In 1974, Baddeley, etc. Based on the analysis of the short-term memory was first proposed working memory (workingmemory) is a kind of information the concept of temporary processing and storage of energy with limited memory systems. In the following years of research, it was found that working memory plays a key role in the completion of complex cognitive tasks such as language understanding, learning, reasoning, and thinking. Currently, most researchers believe the forehead (middle) cortex (mesoprefrontal cortex, mPFC) involved in the implementation process of working memory, control and coordination of information processing in working memory. mPFC area mainly Chinese and dopamine in the ventral tegmental area (ventraltegmental area, VTA) of (dopamine, DA) neurons project can easily be excited by psychological stress, leading to DA depletion of
Working memory produces damage. The purpose of this paper is to investigate the effects of psychological stress on working memory and the effects of tyrosine intervention in the precursor substance DA of the central transmitter .
Materials and Methods
First, the material
1. Animals: purebred Sprague2Dawley (SD) 40 male rats, weighing 180 ~ 220g, Naval Medical Research Institute of Experimental Animal Center offers.
2. Equipment: eight-arm maze: a smooth plate made of plastic, placed 75cm high from the ground, the center diameter of the platform 51. 5cm, each arm of the eight-arm
It is 60cm long and 11cm wide , and the arm side panel is 10cm high and transparent. Each arm is 3cm away from the distal end , and a 1cm deep and 2cm diameter bait pit is set ; Com2municationBox psychological stress model.
3. The reagent : tyrosine , relative molecular weight of 181. 19, provided by Shanghai United Food Additives Co. , Ltd. , purity > 98. 0% .
Second, the method
1. Animal treatment : The single cage is kept in the soundproof room , and the light / dark cycle is 12h/12 h ( reversing the circadian rhythm of the experimental rats , the illumination time is
18 : 00 ～ 06 : 00, 06 : 00 ～ 18 : 00 is a dark cycle , using 40W incandescent lighting , so that the maze training and measurement in the dark cycle ) . The temperature is (23 ± 2) °C. Free eating normal diet before the experiment, adapt to 1 week. Limit food intake , control animal weight to drop to about 85% and maintain , then start labyrinth training and experimentation. During training and experiment every day to 18:00 (after training and testing is complete) feeding, to ensure that food deprivation in the first two days of training and testing. 2. Maze training : At the beginning of 3d, the rat is placed on the central platform of the maze , allowing free exploration and eating of bait scattered in the maze to adapt. (The bait formula is : milk powder 6mg, lactose 23mg, low-substituted hydroxy cellulose 2. 5mg, magnesium stearate 0. 5mg, talc powder 1mg, powdered sugar 17mg . After granulation , the tablet press is pressed into 50mg / tablet ) . Later, each rat was trained once a day, training 6d a week. During training , only 4 arms were used as food arms , and the same rats were fed until the end of the experiment , but each rat was in 4 directions to reduce the odor clues. Each rat was wiped with alcohol to remove his excrement after training. Rats have eaten 4 food arms or made 14 choices , or 10 minutes.
That is the end of a training session. When the rat has only one error in 4 consecutive trainings , it is regarded as the standard for achieving working memory formation. At this time
It trains twice a week, until all rats are up to standard, ie psychological stress test animals as a working memory formation. Two errors ( statistical cumulative counts ) are recorded during training and testing : entering an arm that has eaten food is a working memory error (working
Memoryerror), enter the no food arm as a reference memory error (ref2erencememoryerror) .
3. Psychological stress : Using the CommunicationBox psychological stress model , the rats were shocked ( shock current is 1 ~ 2mA, cycle
100s, intermittent 90s) exclamation, startle , experimental rats are not subjected to electric shock , but spectator other rats suffering from electric shock , through psychological, auditory and other psychological stress.
4. Experimental grouping : 40 working memory formation rats , according to the weight order , according to the principle of group balance, divided into 5 groups , respectively : blank control group ( do not give psychological stress , feeding ordinary feed 100g / kg body weight ) , psychological stress group ( giving psychological stress , feeding ordinary feed 100g/kg body weight ) , tyrosine intervention group ( giving psychological stress , and giving tyrosine low, medium and high from 0d before the stress exposure) Three doses , namely tyrosine 250, 500 and 1000 mg/kg, were subgrouped , and tyrosine was mixed into normal diet for feeding at 100 g/kg body weight ) . Determination of tyrosine content in common feeds according to the method specified in GB/T18246-2000 ( determination of amino acids in feed ) , determination of tyrosine content by Hita2chi 835-50 amino acid automatic analyzer
0. 53% (5. 3mg / g) .
5. Experimental procedure: Each psychological stress 08: 00-10: 00, 30min / (sub-group), 1 times / d, continuous 14d. Stress is placed in the control group without electrical stimulation device, in order to keep the experimental conditions exactly. Working memory errors and reference memory errors were measured immediately after the end of stress on days 1, 4, 7, 10, and 13 for each group .
6. Data statistics : The data representation uses x ± s x, and the statistical analysis uses the ANOVA method.
Result
1. Maze training : The working memory error of the eight-arm maze training in rats and the reference memory error are shown in Figure 1 . From the first week of working memory errors (1. 43 ± 0. 28, n = 40), the reference memory errors (4. 33 ± 0. 63, n = 40) to 10 weeks working memory error (0. 05 ± 0 02, n=40) , reference memory error (0. 12 ± 0. 04, n=40) reaches a relatively stable specified level and can be regarded as working memory formation.
2. The effect of psychological stress on the working memory: The results are shown in Table 1, 2, compared to the control group, the first group of psychological stress, 7, 10, 13 days significantly increased working memory errors, all the time The measured reference memory errors were higher than the control group , indicating that the psychological stress impaired the spatial working memory ability of the rats.
3. The effect of tyrosine intervention on psychological stress : as seen in Tables 1 and 2 , compared with the psychological stress group , rats in each group of 1000 mg/kg and 500 mg/kg were treated with tyrosine intervention in different stress days. There are different levels of working memory errors and reduced reference memory errors. 1000mg / kg group showed significant decrease of working memory errors at 7 days and 13 days, at day 4
And on the 10th day, there was a significant decrease in reference memory error. The working memory error and the reduction of reference memory errors on day 10 of the tyrosine 500 mg/kg group were also statistically significant. There were no statistically significant changes in the tyrosine 250 mg/kg group. This suggests that high-dose tyrosine can reduce the damage of working stress to working memory earlier . 500mg/kg of tyrosine also has a certain effect on reducing the working memory damage caused by long-term psychological stress.
Discuss
1. Working memory animal model of this experiment : In humans , current psychobehavioral, neuropsychological, and neuroimaging studies have accumulated a large amount of evidence on the study of working memory , and found that there are at least two types of working memory systems , namely Words work memory (ver2balworkingmemory) and spatial work memory (spatial work2ingmemory), while the establishment of animal working memory model relies mainly on spatial working memory. Smith et al. believe that spatial working memory includes two aspects of information storage and retelling , controlled by different brain regions. Selective attention space comprising repeat spatial position, this experiment employed the use of eight-arm radial maze overall space environment, animal selective attention and investigated the ability of rehearsal space, working memory errors, the reference memory errors can more accurately reflect the animal search capabilities and the ability to repeat, is an ideal spatial working memory in animal models. Woodsom et al. recently pointed out that the radial maze is still one of the best animal models for studying learning and memory.
2. The psychological stressor of this experiment : In the past, most psychological stress animal experiments rely on restraint, electric shock, cold, fatigue and other means , there are too many physical physical stimulation. At present , there are two ways to simulate relatively pure psychological stress . One is to study the effect of psychological stress by equal physical stimulation and compare different sequential stimulation orders . The other is the Com2municationBox model of this experiment. , the use of electric shock mouse mice look on in horror, jumping, screaming, psychological stress through visual, auditory, from largely avoided physical stimulation for the animals, it can be considered more
Pure psychological stress.
3. This experiment observed that psychological stress impairs working memory ( Tables 1, 2). The mechanism may be that mPFC participates in the process of information processing that controls and coordinates working memory. Studies using primate or rodent models have found that working memory defects result from the destruction or removal of mPFC , which can also be reproduced by depletion of DA in mPFC or by blockade of DA receptors. These studies indicate that the DA system of mPFC is the key to the working memory process, and this advanced cortical function is dependent on mPFC . This system exhibits increased activity against almost all stresses , and its DA metabolism and DA release have "priority activity" , even if it is not sufficient to cause a very mild stress of central norepinephrine (NE) changes , such as low Intensive foot shock , mild noise stimulation
It can also cause an increase in the release of DA from the prefrontal cortex . This is because the DA neurons mPFC compared with DA neurons in other brain regions, the lack of presynaptic D2 receptors. This feature enables only the prefrontal cortex DA neurons not only control and regulation of D2 autoreceptors, in turn may be rapidly released DA play effect even at a very mild stress, causing depletion of DA. Further, since the mPFC DA neurons in the VTA from the projection, VTA neurons neurotransmitters other variations may also affect the function of mPFC stress. Kalivas et al. pointed out that some of the afferent pathways of VTA have been shown to play a role in the stress-inducing mPFCDA system, and many neurotransmitters can affect the function of mPFCDA cells in VTA afferents , including 52HT , NE , Ach , GABA. , opioid peptides, excitatory amino acids ( such as : glutamine ) and neuropeptides ( such as : substance P ) . More in-depth exploration and research is needed in these areas.
4. Tyrosine Intervention: neutral aromatic amino acids tyrosine, can be supplied in the diet, but also from the conversion of phenylalanine. US military research shows that 150mg/kg tyrosine oral can improve the clear thinking ability of soldiers during stress, and sufficient tyrosine intake can improve the brain's intelligence analysis ability. 5, 1å’Œå€å€ã€‚ The experiment was carried out with 250, 500, 1000mg / kg three doses , equivalent to the amount of tyrosine given in the feed of the experiment was 0.5, 1 and 2 times. The results demonstrate tyrosine intervention during stress damage to the working memory has a protective effect, although the administration of 1000mg / kg of tyrosine is not immediately reduce stress damage to the working memory, but it can accept more stress early (Day 4) Reduce the degree of stress damage to working memory. The 500 mg/kg tyrosine intervention also has the effect of reducing working memory impairment caused by longer-term psychological stress. Lieberman et al pointed out that the special nature of the work determines its Navy personnel faced with sleep deprivation and many other stress factors, likely to lead to a decline in operational efficiency. For complex stress factors
Jobs such as maritime operations, tyrosine is possible to improve the efficiency of workers, reduce operational errors, and therefore has a good prospect. Future work should focus on further population intervention studies with a view to obtaining more evidence.
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