JP2016131556A - Model animal having depression causing sleep abnormality - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a model animal having depression causing sleep abnormality, and a production method thereof.SOLUTION: In a production method of a depression model rat in a test rat, the test rat is bred together with a Brown Norway rat. A depression model rat produced by the method is also provided.SELECTED DRAWING: None

Description

   The present invention relates to a model animal of depression that causes sleep abnormalities and a method for producing the same.

  Stress caused by social relationships including human relationships is one of the major factors that cause pathological conditions such as mood disorders and associated sleep disorders. Among mood disorders, major symptoms such as eating disorders, fatigue, and sleep disorders appear in addition to core symptoms such as depression, loss of interest and joy in major depression. In particular, in sleep disorders, characteristic findings such as sleep disturbance such as prolonged sleep latency, awakening during sleep, increased REM sleep, and shortened latency are recognized. These abnormalities are often not sufficiently improved by taking sleeping pills alone, in which case they are the target of treatment with antidepressants.

As described above, major depression is divided into subjective mood disorders and behavioral disorders, and the latter has been extensively studied using various animal models. In recent years, a “social defeat stress” model using mice has been reported and has received much attention1 ⁾ . In this animal model, mice are brought into contact with another large body mouse for 10 days, and social stress is applied. However, over half of the stressed mice continue to interact with other mice over a long period of time. Avoid contact. This avoidance behavior is considered to be an indicator of depression-like behavior because it is similar to the symptoms of depression and improved by chronic administration of antidepressants ¹⁾ . The avoidance behavior due to social defeat stress is a characteristic finding in mice, and stress loading methods are being established methodologically, and it is possible to induce avoidance behavior relatively easily.

On the other hand, in rats, there have been no reports of successful cases of showing avoidance behavior even when similar stress is applied. Recently, it has been reported that rats show relatively high prosocial behavior that supports the survival behavior of other individuals ²⁾ , and there is no similar report in mice. It is assumed that the susceptibility when subjected to mechanical stress is more greatly affected than in mice. Therefore, we considered the importance of inducing social avoidance behavior in rats.

  In addition, in order to conduct a detailed study of sleep disorders that are observed at high rates associated with depression, analysis using model animals is necessary, but there have been appropriate animal models that reproduce human pathologies. However, the mechanism of sleep disorder development remained unknown.

Krishnan V, Han MH, Graham DL, Berton O, Renthal W, Russo SJ, Laplant Q, Graham A, Lutter M, Lagace DC, Ghose S, Reister R, Tannous P, Green TA, Neve RL, Chakravarty S, Kumar A , Eisch AJ, Self DW, Lee FS, Tamminga CA, Cooper DC, Gershenfeld HK, Nestler EJ. Molecular adaptations underlying susceptibility and resistance to social defeat in brain reward regions. Cell. 2007. 131 (2): 391-404. Ben-Ami Bartal I, Decety J, Mason P. Empathy and pro-social behavior in rats. Science. 2011. 334 (6061): 1427-30.

The inventor has established a new psychosocial stress paradigm that modifies social psychological stress using rats, i.e., social defeat stress, and has established a methodology that can induce social avoidance behavior, including sleep disorders. Another object of the present invention is to develop a model animal that can more accurately express clinical symptoms of human depression.
Accordingly, an object of the present invention is to provide a model animal that causes sleep abnormalities and exhibits depression-like behavioral abnormalities, and a method for producing the same.

As a result of intensive studies to solve the above-mentioned problems, the present inventor used Brown Norway rats (BN rats) as stressor rats and reared the test rats together with the BN rats, thereby depressing the test rats. The present inventors have found that such symptoms can be caused and have completed the present invention.
That is, the present invention is as follows.
(1) The method for producing a psychiatric disease model rat in the test rat, comprising breeding the test rat together with a Brown Norway rat.
(2) The method according to (1), wherein the test rat is a Wistar rat or a Sprague Dawley rat.
(3) The method according to (2), wherein the age at the start of stress loading of the test rat is 8 weeks old.
(4) The method according to (1), wherein the Brown Norway rat is 7 months old or older.
(5) The mental illness is at least one selected from the group consisting of depression, acute stress disorder, sleep disorder, anxiety disorder, eating disorder and post-traumatic stress disorder (1) to (4) The method of any one of these.
(6) A mental disease model rat produced by the method according to any one of (1) to (5) above.
(7) Contact avoidance behavior for Brown Norway rats or rats of the same kind as test rats, reduction of total distance traveled, anxiety-like behavior due to elevated plus maze, weight loss, reduced food intake, reduced preference for sucrose, non-REM The rat according to (6), which represents at least one characteristic selected from the group consisting of a decrease in the appearance time of sleep and a fragmentation of the appearance of non-REM sleep and REM sleep.
(8) The mental illness is at least one selected from the group consisting of depression, acute stress disorder, sleep disorder, anxiety disorder, eating disorder and post-traumatic stress disorder (6) or (7) Rat according to.
(9) A screening method for an antipsychotic drug, comprising bringing a candidate substance into contact with the model rat according to any one of (6) to (8) or a tissue thereof.
(10) The method according to (9), wherein the mental illness is at least one selected from the group consisting of depression, acute stress disorder, sleep disorder, anxiety disorder, eating disorder, and post-traumatic stress disorder. .

  According to the present invention, a model rat for mental disorders such as depression and a method for producing the same are provided. The rat of the present invention is extremely useful in that it can be used for, for example, analyzing the mechanism of depression, screening for a novel antidepressant, and the like.

It is a figure which shows the implementation method of social defeat stress. Use special breeding cages that can be equipped with food boxes and activity sensors. A bottle containing water and sucrose can also be installed, and a selective intake test of water and sucrose can also be conducted. It is a figure which shows the interaction test result after stress loading. It is a figure which shows each group comparison result of the contact rate in the interaction test after stress load. It is a figure which shows the weight transition of the rat after stress loading. It is a figure which shows the actogram recording in each group rat. It is a figure which shows each group comparison result of the appearance time of each sleep stage in the light period. It is a sleep figure of each group rat in the light period. It is a figure which shows the latency according to group until the non-REM sleep after the light period start appears.

1． Overview Major depression is a mental illness that manifests core symptoms such as depressed mood or loss of interest and joy, as well as physical symptoms such as decreased appetite, fatigue, and sleep disorders. In the present invention, a new social psychological stress paradigm that modifies social defeat stress was constructed, and an attempt was made to develop a model animal that can more accurately express clinical symptoms of human depression. As a result, it was the first time that rats were able to induce social avoidance, a behavioral indicator of depression, and objective measurement of avoidance behavior became possible. This rat model not only shows anxiety symptoms and physical findings characteristic of depression, but also sleep wake disorder, especially REM sleep, which has not been reported in previous social stress models. A related abnormality was found. These findings are thought to accurately reflect human clinical symptoms compared to conventional depression models, and development of diagnosis, treatment, and prevention methods for depression from a different perspective than the conventional disease concept Expected to be useful.

  The present inventor succeeded in inducing avoidance behavior against other individuals for the first time in rats using an experimental system that loads social psychological stress. Since the avoidance behavior was shown not only in rats of the same strain as the stressor but also in rats of the same strain as the test rat, the model animal we developed causes generalization in avoidance behavior. Became clear.

In social defeat stress in mice, it has been reported that avoidance behavior to other individuals can be completely recovered by chronic administration of antidepressant drugs1 ⁾ , so this avoidance behavior is considered to be a behavioral indicator of depression-like state ing. As for avoidance behavior in our model animals, chronic administration of imipramine, a tricyclic antidepressant, showed only partial recovery. Therefore, it can be pointed out that mechanisms other than monoamines in the brain may be involved in the induction of avoidance behavior.

  In addition to the avoidance behavior described above, there was a decrease in locomotor activity, such as a significant reduction in the total travel distance per fixed time. This seems to reflect the human psychomotor deterrence. In addition, abnormalities similar to physical symptoms characteristic of depression, such as weight loss and reduced eating behavior, were confirmed, and sucrose intake and preference decreased. This decrease in palatability is thought to reflect human anxiety-like condition (anhedonia), and the improvement of the antidepressant is shown in this model. It is presumed that the aspect of the symptom is imitated very well.

  In animal models of depression that have been reported so far, abnormalities in sleep organization, particularly abnormalities in REM sleep, when accompanied by a depression-like state have not been well examined. In our model, the appearance of non-REM sleep has been significantly reduced, and conversely sleep sleep has occurred, with increased REM sleep. It was significantly reduced. In addition, the appearance latency of non-REM sleep shows a tendency to be prolonged, suggesting the possibility of so-called sleep deprivation, and the REM sleep latency is significantly shortened. Very similar findings were obtained. These sleep abnormalities have been significantly improved by chronic administration of antidepressants. As for sleep abnormalities in depression, there have been some cases where non-REM sleep is fragmented by various stresses on animals, but REM sleep abnormalities, especially shortening of latency and fragmentation, appearance time There have been no reports on animal models that show the phenomenon of significant increase in According to the present invention, an animal model exhibiting REM sleep disorder associated with depressive symptoms could be constructed for the first time.

Furthermore, this model showed behavioral characteristics that all animals under stress avoid other individuals. This is a significant difference from the previous report ^{1) where the} avoidance rate due to social defeat stress in mice is about 50%. Therefore, the stress loading method based on the combination of animal strains used in this model is effective in inducing the avoidance behavior of the animals, which is very useful for screening the anti-depressant drugs. It has an excellent advantage. This utility can be expected not only for the development of new drugs but also for various safety tests after development.

Regarding neuropathology in depression, postmortem brain studies in psychiatric disorders suggest an association between abnormalities in the brain oligodendrocyte system and mood disorders. Oligodendrocytes play an important role in the formation of normal jump conduction of nerve impulses as an element constituting the myelin sheath (myelin sheath) in nerve cell axons. It was found that oligodendrocyte lineage cells were specifically reduced in the frontal poles of the brain4 ⁾ . Recently, it has been reported that oligodendrocyte progenitor cell regeneration is promoted during REM sleep5 ^), and the relationship between oligodendrocyte lineage cells and REM sleep abnormalities is very interesting. is there. Therefore, a detailed pathological study of this model exhibiting REM sleep abnormalities may reveal a new pathological mechanism of depression that does not depend on the monoamine pathological hypothesis.

  In recent years, intractable depression in which treatment with antidepressants has not been successful has become a clinical problem. The model animal of the present invention can be screened for pharmaceuticals for such intractable depression.

2. The present invention relates to a method for producing a mental disease model rat in the test rat, characterized in that the test rat is reared together with a Brown Norway rat.

(1) Test rat A test rat is a rat for which a psychiatric disease model rat is prepared, and the type thereof is not limited. Examples of test rats include Wistar (WI) rats, Sprague Dawley (SD) rats, and Long-Evans rats, and SD rats are preferred.
The age of the rat is not limited and is preferably 5 to 8 weeks, more preferably 8 weeks. In the present invention, it is preferable that the age at the start of stress loading is 5 to 8 weeks, for example, 8 weeks.
The rat may be bred by itself, or a commercially available rat (Nippon Charles River) may be used.
However, it is necessary that the test rat is not a Brown Norway rat used for a stressor described later.

(2) Stressor rat The stressor rat means a rat that gives stress to the test rat. Although there are many types of stress, in the present invention, stress using a social psychological load method including direct and indirect contact with other individuals, such as social defeat stress, is mentioned.
Examples of the stressor rats include Brown Norway (BN) rats, and the age to be used is not particularly limited as long as the body is larger than the test rats and has aggressiveness. 9 months old, more preferably 9 months old or older.

(3) Rearing In order to apply stress to the test rat, the test rat and the stressor rat are reared together in a cage. The breeding method may be a direct method or an indirect method, and both may be used in combination. In the case of the direct method, the breeding period for applying stress is 5 minutes to 1 hour, preferably 10 minutes to 15 minutes. In the direct method, when the animal is reared, the stressor rat makes contact such as tracking or covering the test rat (referred to as “interaction”).
In the indirect method, the test rat and the stressor rat are allowed to stay for about 1 to 48 hours in a breeding cage separated by a squeezing plate. Preferably it is 24 hours. In this case, the threshold plate is preferably a transparent plate.

(4) Psychiatric disorders In the present invention, the target mental illness is not particularly limited, and examples thereof include depression, acute stress disorder, sleep disorder, anxiety disorder, eating disorder, and post-traumatic stress disorder. And one or more can be targeted. In the present invention, depression is preferable among these mental disorders. Since these diseases often have symptoms common to some of them, or a part of them, a model of the disease can be obtained by performing behavioral evaluation described later.

(5) Behavioral evaluation Confirmation of whether a rat after stress loading has exhibited a predetermined mental illness such as depression, that is, confirmation that it has become a model rat can be selected from the following methods, for example: it can. Evaluation items may be used alone or in combination.
(i) Avoidance behavior When the contact behavior is measured in an open field, the contact ratio (labeled Ratio in the figure) to a stressor rat (BN rat) or a rat of the same kind as the test rat (SD rat is preferred) is less than 100%. Is an indicator of mental illness (depression, acute stress disorder, post-traumatic stress disorder, etc.). When a stress is applied to the test rat, not only the stressor rat but also the same kind of rat as the test rat takes an avoidance action.
(ii) Behavioral trajectory and travel distance When values in the stress load group are shortened with a significant difference compared to controls, such as depression, acute stress disorder, anxiety disorder, post-traumatic stress disorder, etc. Use as an indicator.
(iii) Anxiety-like behavioral test using elevated plus maze When the stay time on the open arms in the stress load group is shortened with a significant difference compared to the control, depression and acute stress disorder , Indicators of anxiety disorder, post-traumatic stress disorder, etc.
(iv) Body weight measurement When the body weight is reduced by about 20% compared to the control, it is used as an index for depression, acute stress disorder, anxiety disorder, eating disorder, post-traumatic stress disorder.
(v) Measurement of food intake When food intake is reduced by about 40% compared to controls, it is used as an indicator of depression, acute stress disorder, anxiety disorder, eating disorder, post-traumatic stress disorder.
(vi) Observation of palatability for sucrose When palatability decreases with a significant difference compared to controls, such as depression, acute stress disorder, anxiety disorder, eating disorder, post-traumatic stress disorder, etc. Use as an indicator.
(vii) REM sleep and / or non-REM sleep appearance time When REM sleep has a significant increase in appearance time compared to the control, or non-REM sleep has a significant shortening compared to the control Is an indicator of depression, acute stress disorder, sleep disorder, anxiety disorder, post-traumatic stress disorder, etc. In this case, it is determined that REM sleep and / or non-REM sleep are fragmented when the count of the number of appearances of a continuous sleep phase for a certain time or more is significantly increased compared to the control group.

3. Method for Screening Antipsychotic Drug The present invention provides a method for screening an antipsychotic drug characterized by bringing a candidate substance into contact with the mental disease model rat prepared as described above or a tissue thereof.
The present inventors have found that the model rats of the present invention exhibit a depression phenotype (symptoms of mental / neurological diseases). Based on this finding, if any substance can be confirmed to have an effect of alleviating or reducing depression symptoms in the model rat, the substance can be used as an antipsychotic drug.

  Candidate substances are not particularly limited, and existing drugs (for example, existing antidepressants, other neurodegenerative diseases, anti-inflammatory drugs, various receptor agonists and antagonists, ion channel promoters and inhibitors, blood components) In addition, it may be in any form such as a peptide, a low molecular compound, a high molecular compound, a salt or precursor thereof, and the like.

Specifically, the present invention includes the following steps.
(A) a step of bringing a candidate substance into contact with the model rat of the present invention or a tissue thereof (b) a step of examining reduction of depression symptoms in the administered rat. In the screening method of the present invention, depression, acute stress disorder, A therapeutic agent for diseases such as sleep disorder, anxiety disorder, eating disorder, and post-traumatic stress disorder can be screened, and a therapeutic drug for depression is preferably screened.

  When the model rat itself is used, “contact” includes a mode in which a candidate substance is administered to the model rat. Administration may be oral or parenteral. That is, the administration route of the candidate substance is not particularly limited as long as it is a route that is generally adopted for drug administration. For example, oral, sublingual, nasal, transpulmonary, transgastrointestinal, Examples include skin, eye drops, intravenous injection, subcutaneous injection, intramuscular injection, intraperitoneal injection, local injection, and surgical implantation, and oral administration is preferred.

The item to be inspected in the step (b) is at least one of the following (i) to (vii).
(i) Contact avoidance behavior
(ii) Action trajectory, distance traveled
(iii) Anxiety-like behavior test using elevated plus maze
(iv) Body weight measurement
(v) Food intake measurement
(vi) Preference observation for sucrose
(vii) REM sleep and / or non-REM sleep appearance time

  If at least one of the above-mentioned items is improved by contact with a candidate substance, the candidate substance can be selected as an antidepressant.

  In the screening method of the present invention, when a model animal tissue is used, a tissue may be collected from the model animal and a candidate substance may be brought into contact with the tissue. The contact method includes an aspect in which a candidate substance is added to a tissue section, an aspect in which tissue is cultured in the presence of the candidate substance, and an aspect in which constituent components of the tissue are extracted after contact with the candidate substance.

After the contact, the index is an abnormality of glial cell lineage, in particular, reduction of myelin sheath abnormality of nerve axon accompanying decrease of oligodendrocyte lineage cell line. For example, a brain section is prepared from a model rat administered with a candidate drug, a test substance is brought into contact with the brain section, and then labeled by an antibody immunostaining method or the like, and the labeled section is observed with a microscope. As a result of this observation, it can be said that the symptom is reduced when the candidate drug-using tissue exhibits an abnormal change including the above-mentioned index as compared with the non-contact tissue. In addition, when the blood components of model rats after contact are extracted and adjusted, and the amount of depression-related substances in each component is examined, the depression-related substances change to a range equivalent to that at the time of non-contact. It can be said that the symptoms were reduced.
Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

Method 1. Method of stress loading The test rat used in the experiment (referred to as “test rat” in this example) was basically kept individually. The procedure that became the standard for the new social defeat stress load was implemented as follows (Fig. 1). First, one small test rat to be tested was invaded into the cage where a large, more aggressive strainer rat was raised. Two rats interacted for 10 minutes, and the stressor rat made contact with the test rat, such as following or covering (direct contact) and not causing any extraneous trauma (direct contact) After that, the test and stressor rats were allowed to stay together for 24 hours in a breeding cage separated by a slab (indirect contact). The crisp board is transparent and uses a shape that has holes in some places. Although two rats cannot make direct contact with each other, sensory information such as scent, cry, and vision are not blocked. It was in a state. The next day, stress was applied in the same procedure, but the stressor rat was a different individual from the rat used the previous day. Under these conditions, stress was applied once a day for 5 consecutive days, and then a method of presenting only indirect contact for 2 days was performed twice. Therefore, the stress load under the condition of combining direct contact and indirect contact was implemented 10 times in total.

2. Behavioral assessment of stress Before and after the start of the stress loading described above, an interaction test was conducted on test rats in the open field. A small box is placed in the open field to hold the social target (stressor rat or rat of the same strain as the test rat) to be contacted with the test rat. Rats were allowed to move freely for 2.5 minutes, and the behavioral trajectory and distance traveled were measured using behavior analysis software Time OFCR4 (O'HARA & CO, Ltd.). Thereafter, the same measurement was performed under the condition that the Social target was placed in a small box, and the time when the test rat entered the interaction zone was measured. The contact rate, which is an index of avoidance behavior for other individuals, is the stay in the interaction zone when the social target is in the box, with the stay time in the interaction zone being 100% when there is no social target in the box. The percentage of time (indicated as Ratio in the figure) was calculated.

  In addition, we conducted an anxiety-like behavior test using an elevated plus maze after stress loading. Open arms and Closed arms (110 cm x 110 cm) were placed at a height of 50 cm, and animals were allowed to move freely on the arm for 5 minutes. The evaluation of anxiety-like behavior was calculated from the time spent in Open arms.

3. Physiological evaluation of stress During the series of experiments including before and after stress loading, the amount of activity was measured. After stress loading, we measured the amount of action under constant dark conditions for some groups, and confirmed the free continuation rhythm. Moreover, in order to confirm the presence or absence of abnormal eating behavior associated with stress loading, body weight measurement and food consumption were measured before and after stress loading. In addition, rats were allowed to choose to take water and a 1% sucrose solution, and each intake was measured. The preference for sucrose was calculated as the ratio of the intake of 1% sucrose solution to the intake of all solutions including water and 1% sucrose solution. Furthermore, to investigate the effects of stress on sleep-wake patterns, chronic electrode implantation was performed to record brain waves in rats, and sleep-wake brain waves 24 hours before and after stress loading were recorded. Since the electroencephalogram recording takes a long time, it is necessary to suppress the movement of animals and the generation of noise from the outside, so we made precise measurements using our own built-in operational amplifier type EEG cable ³⁾ .

4). Drug administration experiment From the next day after the end of stress loading, chronic administration of imipramine (20mg / kg, ip) once a day for 25 days, behavioral behavior for avoidance behavior and sleep-wake rhythm with other individuals Physiological evaluation was performed. In addition, for the control group of the drug administration experiment, 0.9% physiological saline was intraperitoneally administered chronically.

Result 1. Selection of strains used for stress loading The strains of the stressor rat and the test rat were selected to induce avoidance behavior by the modified new social defeat stress.
(i) When 6-week-old Wistar (WI) rats were used as test rats and 8-week-old WI rats were used as stressors at the start of stress, the contact rate in the interaction test after the end of the stress period was 149.0 ± 13.6% The contact rate into the interaction zone was promoted.
(ii) In the combination of 5 weeks old Sprague Dawley (SD) rats as test rats and 8 weeks old WI rats as stressors, the contact rate was 137.9 ± 8.5%, and increased contact behavior was observed as before. .
(iii) When 8 weeks old SD rats were used as test rats and 7 months old Brown Norway (BN) rats were used as stressors, the contact rate was 6.2 ± 5.1%, and contact avoidance behavior was induced. Based on these judgments, a method using SD rats as test rats and BN rats as stressors was selected as a combination of appropriate strains. In addition, BN rats were retired rats that had high contact rate and sensitivity to other individuals.

2. Behavioral evaluation by new social defeat stress and effect of antidepressant imipramine A small box that can hold a social target rat (in this case, a large rat that became a stressor) is placed in the open field. The contact with the social target is evaluated by the intrusion time in the interaction zone provided in the peripheral area of the box (calculated as contact rate = stay time when the social target is present / stay time when the social target is not present × 100). In the control group, when the Social target is present, the intrusion time into the interaction zone is increased as compared with the case where the Social target is not present. On the other hand, when there is a social target, the test rat loaded with stress significantly reduces the intrusion time into the interaction zone and takes avoidance action on the social target.
In the interaction test, when the BN rat stayed in the open field box (social target), the contact avoidance behavior that the time for the test rat to enter the interaction zone significantly decreased from the first time after the stress was induced. (Figure 2).

This contact avoidance behavior lasted for about 3 months after stress loading. Furthermore, even when the social target in the interaction test was the SD rat of the same strain as the test rat, contact avoidance behavior was induced after the first stress, and a significant decrease in contact rate was confirmed even three months after the end of stress. It was done.
Specifically, in FIG. 3, each group comparison of the contact rate in the interaction test after stress loading is shown. The control group showed an average contact rate of over 200% against the Social target. In the interaction test after the initial stress, a significant reduction in contact rate with the stressor rats occurred in the stress group (FIG. 3A). Furthermore, the contact behavior was similarly reduced in rats of the same strain as the test rat (FIG. 3B). The phenomenon was confirmed continuously for one week after the end of stress loading (Figs. 3C and D) and one month later (Figs. 3E and F) (Note: C and E are stressor rats, D and F are test rats) And the results when rats of the same strain as social targets were shown).

Chronic administration of imipramine, a tricyclic antidepressant after the end of stress, significantly improved contact avoidance behavior for social targets (BN rats and SD rats) compared to the untreated stress group at 1 week after the end of stress When the social target was BN rats, the same tendency was observed even at 1 month after stress (FIG. 3E). No significant difference was observed when the social target was the same strain as the test rat (FIG. 3F). One month after the stress, a significant difference was confirmed between the administration group and the control group, and it was found that a complete improvement effect up to the level of the control group could not be obtained.
The total distance traveled by the test rats in the open field for 2.5 minutes was 628 ± 62 cm in the stress group at 1 week after the end of stress, which was significantly reduced compared to the value in the control group (839 ± 79 cm) .

  After the stress, the anxiety-like behavior of the elevated plus maze was evaluated. The stay time in the open arms of the stress group was 21.7 ± 9.87 seconds, which was significantly reduced compared to the stay time in the control group (68.8 ± 22.8 seconds). In the chronic administration group of imipramine, the residence time was 44.4 ± 11.5 seconds, showing a recovery tendency, but did not reach a complete recovery to the control group level.

3. Measurement of physiological indices and sleep-wake rhythm Body weight decreased significantly after the first stress (P <0.01), and remained significantly lower for 23 days after the end of stress compared to the control group (Fig. 4A). In addition, as for the eating behavior, the intake decreased significantly (P <0.01) after the first stress, and continued until one week after the end of stress. In the intake selection test of water and 1% sucrose solution, the sucrose intake one month after the end of stress was significantly lower than the control group (P <0.01), which was significantly improved by chronic administration of imipramine (P <0.01), but did not reach full recovery to control level. Furthermore, the preference for sucrose one month after the end of stress showed a significant decrease (P <0.05) in the stress group compared to the control group, and was completely recovered to the control group level by chronic administration of imipramine (P < 0.05) (FIG. 4B).

In order to investigate the effect of stress on free continuation rhythm, the amount of behavior in the control group, stress group and imipramine administration group was measured under constant dark conditions. FIG. 5 shows the recorded actograms of the control group (FIG. 5A), the stress group (FIG. 5B), and the imipramine administration group (FIG. 5C). The blue part of the record shows the period of stress (Figure 5B, C). During the stress period, the amount of behavior during the light period increased. After stress loading, the continuous rhythm of each group was measured by changing to constant dark conditions. In the control group (FIG. 5A), a slow rhythm regression occurred due to constant dark conditions, but in the stress group, the regression was more prominent (FIG. 5B).
By the administration of imipramine, the rhythm regression that occurred in the stress group was advanced to the control group level (FIG. 5C). When the amount of behavior of each individual was averaged every hour, an increase in the amount of behavior was observed in the early stage of the light period in the stress group, and administration of imipramine had the effect of reducing it (FIG. 5D).

  Furthermore, we examined the effects of stress on sleep-wake patterns by electroencephalogram analysis. In FIG. 6, each group comparison of the appearance time of each sleep stage in the light period is shown. There is no significant difference in the sleep time in the light period in each group, but the appearance time of non-REM sleep is significantly decreased (P <0.01), and conversely, REM sleep is significant compared to the control group Appearance time increased (P <0.01). Chronic administration of imipramine improved these phenomena to the control group level (Figure 6).

  In FIG. 7, the typical example of the sleep figure of the control group and stress group in a light period is shown (FIG. 7A). In the stress group, the number of REM sleep appearances is clearly increasing. When the total appearance time and fragmentation values for each sleep stage are plotted (FIG. 7B), the increase in appearance time and fragmentation are promoted in the stress group compared to the control group in REM sleep, and the imipramine administration group is the control. It was similar to the group distribution pattern. In non-REM sleep, a decrease in total appearance time and an increase in fragmentation were observed in the stress group, and imipramine administration showed a distribution pattern similar to that in the control group.

  FIG. 8 shows the latency by group until non-REM sleep appears for the first time after the start of the light period (FIG. 8A). Compared to the control group, the stress group showed a tendency to extend and appeared later. The administration of imipramine shortened the appearance latency. The time until the appearance of REM sleep after the appearance of non-REM sleep (FIG. 8B) was significantly shortened (P <0.05) in the stress group. imipramine showed the action to prolong the appearance latency of REM sleep.

References
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Claims (10)

  A method for producing a psychiatric disorder model rat in the test rat, comprising breeding the test rat together with a Brown Norway rat.   The method according to claim 1, wherein the test rat is a Wistar rat or a Sprague Dawley rat.   The method according to claim 2, wherein the test rat is 8 weeks old at the start of stress loading.   The method according to claim 1, wherein the Brown Norway rat is 7 months or older.   The psychiatric disorder is at least one selected from the group consisting of depression, acute stress disorder, sleep disorder, anxiety disorder, eating disorder, and post-traumatic stress disorder. The method described in 1.   A psychiatric disease model rat produced by the method according to any one of claims 1 to 5.   Brown Norway rats or rats of the same kind as test rats, contact avoidance behavior, reduction of total distance traveled, anxiety-like behavior due to elevated plus maze, weight loss, reduced food intake, reduced preference for sucrose, appearance of non-REM sleep The rat according to claim 6, which represents at least one characteristic selected from the group consisting of a decrease in time and a fragmentation of the appearance of non-REM sleep and REM sleep.   The rat according to claim 6 or 7, wherein the mental illness is at least one selected from the group consisting of depression, acute stress disorder, sleep disorder, anxiety disorder, eating disorder and post-traumatic stress disorder.   A method for screening an antipsychotic drug, comprising bringing a candidate substance into contact with the model rat according to any one of claims 6 to 8 or a tissue thereof. The method according to claim 9, wherein the mental illness is at least one selected from the group consisting of depression, acute stress disorder, sleep disorder, anxiety disorder, eating disorder, and post-traumatic stress disorder.