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UDC 159.972:575:57.08472972
MODERN APPROACHES TO THE STUDY OF THE GENETICALLY DETERMINATED STABILITY OF LABORATORY ANIMALS TO STRESSOR LOADS (REVIEW)
P.K. Anokhin Research Institute of Normal Physiology, Moscow V.G. Bashkatova, S.K. Sudakov
Despite a large number of studies concerning the emotional stress, the exact mechanisms of anxiety disorders still remains unclear. The review analyzes data concerning lines of inbred animals with different phenotypes of emotional-stress reactions. At present, the lines of animals with different reactions to emotional stress are considered as most adequate models for the study of human anxiety. In the article, further perspective approaches for studying the anxious behavior of animals are considered.
Key words: emotional stress, anxiety, inbred animals with different phenotypes of emotional-stress reactions.
Introduction
Despite a large number of studies devoted to the study of emotional stress, many aspects of the emergence and development of an emotional-stress response remain to this day inadequately studied. According to modern ideas, emotional stress is a systemic reaction of the organism, accompanied by a wide spectrum of metabolic and biochemical changes, both in peripheral tissues and in the structures of the mammalian CNS [1, 2]. At present time, it is well known that anxiety is the first reaction of an organism to a stressful effect. At the same time, pathological anxiety is a serious disorder of the central nervous system (CNS) [3; 4].
Until now, the debatable question is whether pathological anxiety develops as a quantitative variation of the normal state (that is, an excess of "normal" anxiety) or it is a qualitatively different condition [5]. It is generally accepted that pathological anxiety is characterized by an inappropriate expression of anxiety behavior, which includes such phases as the development of "diffuse" hypertension, the interpretation of "dubious" situations as a threat; exaggerated avoidance of dangerous situations and/or exaggerated reaction to the threat [3; 6]. It is known that the spectrum of emotions observed in rats and mice is not as diverse as in humans. At the same time, the anxious behavior of these animals is sufficiently well modulated, and is supposed to have a significant similarity to the anxiety states of humans [7; 8]. It should be noted that most behavioral anxiety tests conducted in rats and mice allow the normal fear/anxiety response of animals to be elucidated, while the pathological anxiety of a person is a response to an inappropriate force in relation to the initial stimulus. According to the classical theory of Spielberg [9], there are always two categories of anxiety in the behavior of man and animal: basic (trait) and situational (state). Basic anxiety is a constant, that is, an innate
characteristic of the body, and situational anxiety depends on the specific situation and varies accordingly the degree of "stress" of the environment [10]. Many existing behavioral patterns of anxiety are based on the study of situational anxiety. These models are widely used, both for studying the neu-robiological mechanisms underlying the anxiety states, and for screening compounds with potential anxiolytic activity [11]. In these studies, a single stress model is used, for example, a elevated cross-shaped labyrinth (ECL), a black and white camera, etc., which makes it possible to simulate acute (situational), rather than basic anxiety [12; 13]. At the same time, in the light of modern concepts, the modeling of basic anxiety seems to be a very urgent task, including from the point of view of applying the results obtained to disturbing human psychology [14]. To model this prolonged (chronic) anxiety in rodents, several approaches are used.
Rats with high and low anxiety
At the present stage of the development of science, one of the most promising directions in the study of pathogenetic mechanisms of anxiety disorders is the study of animals that have genetic differences in the character of emotional-stress reactions. Genetic approaches to the study of behavior make it possible to find out what the variability of the trait is, to what extent it is related to the variability of the genotypes of a given group of animals, and to what extent - with events external to the genotype affecting the central nervous system, and, consequently, behavior. To date, researchers possess several lines of rats and mice that differ in certain aspects of emotional-stressful reactions, including the development of anxiety. Using the following selection criteria, the following rat lines were derived: Modstley (Maudsley Reactive, MR and Maudsley Nonreactive rats, MRA) [15; 16]; Roman (Roman High Avoidance, RHA, Roman Low Avoidance, RLA) [17], Syracuse (SHA
and SLA) [18]; Floripa [19], High Anxiety Behavior (HAB) and Low Anxiety Behavior (LAB) of the rat line [20]. Phenotyping of these lines was carried out on the basis of different behavioral anxiety tests. For example, rapid and slow formation of the reaction of active avoidance of the pain stimulus-electric shock through the floor in the shuttle chamber-was the basis for the separation of the Roman lines of rats (RHA, RL4). In these lines, numerous differences in the behavior of animals were found when testing them in an open field (OF) and an elevated cross-shaped labyrinth (ECL) [17]. The Flori-pa L vs. Floripa H rat line rats were derived by selective segregation according to the level of their motor activity in the central zone in the OF test [19], and the Modstley rats (MR, MNR) - by their behavior in the "defecation" test in the OF [16]. In Russia in the Pavlov Institute of Physiology of RAS USSR, the lines of the KNA and KLA rats (Koltoushi High Avoidance, Koltoushi Low Avoidance), which differ in their behavior under the conditions of an avoided and unavoidable electric shock, were bred. Like other lines of rats, these KNA and KLA lines differ from each other in other behavioral and neurochemical features [13]. At present, there are data on the presence of marked differences in anxiety-like behavior and some other known lines of rats and mice in response to stress effects [21]. In our earlier experiments, it was also shown that Fisher-344 rats had a more pronounced spontaneous-emotional response than Wistar or Sprague-Dawley rats [22].
Other approaches to modeling the emotional-stress response
One of the modern approaches in studying the mechanisms of development of the emotional-stress reaction is the attempt to create the most adequate model of anxiety by using the methods of genetic engineering. It has been established that a person's fear and anxiety, as well as the anxious behavior of animals, are polygenetically determined. However, the modification of one or more genes that play an important role in the pathoge-netic mechanisms of anxiety can largely modulate manifestations of anxiety behavior. The development of genetic engineering and molecular biology made it possible to obtain so-called transgenic animals. To this end, a new genetic material is introduced into the genome of the animal (currently used almost exclusively by mice) - this may be either a DNA section encoding the altered gene already present in the recipient, or a gene from an animal of another species, for example, a rat. In carrying out such studies, special molecular biological methods are used that ensure a sufficiently reliable expression of new DNA in the recipient genome. Otherwise, the fragment introduced into the genome can be preserved in a latent form, without showing activity, and thereby, not revealing itself
[23]. Recently, a description has appeared in the literature of mice with an anxiogenic phenotype [21; 24]. These genetic patterns of anxiety provide an opportunity to examine the contribution of specific genes and products of their expression to the formation of an emotionally-stressful response. However, it should be noted that the main drawback of these models is still the fact that they are all based on the removal of a single gene, whereas the development of an emotionally-stressful reaction involves the modulation of multiple genes. Nevertheless, the method of creating transgen-ic animals provides valuable data on the specific functions of certain genes, including the development of anxiety states, so the list of mice-knockout lines is rapidly replenished.
To study the disturbing behavior of animals, the method of randomized sampling attracts more and more attention of researchers [21]. In recent years, work has appeared in which special mRNA techniques have been used to model heightened anxiety behavior, as a highly effective method of knocking out a gene [25; 26]. One of the promising areas of research is also the study of possible correlations between behavioral responses of fear/ anxiety reactions and changes in neuronal activity in specific brain structures. One of the key tasks is the need to accurately identify specific groups of neurons that can play a leading role in shaping this response. At present, using the methods of functional mapping of the brain of various animal lines, selected taking into account psycho-genetic criteria, seems to be the most promising for solving this problem [27].
In conclusion, it should be noted that the widespread distribution of anxiety disorders in modern society makes the study of the nature of these conditions more urgent. At present, the lines of animals with different reactions to emotional stress are considered as one of the most adequate models for studying the mechanisms of psycho-emotional stress of a person. Thus, the use of animal lines with different responses to emotional and stressful effects can help identify targets for creating a fundamentally new type of drugs that have high anki-olytic activity and low side effects.
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Contacts
Corresponding author: Bashkatova Valentina Ger-manovna, Doctor of Biological Sciences, Professor, leading research worker of the Laborotory of physiology of P.K. Anokhin Research Institute of Normal Physiology, Moscow. 125315, Moscow, ul. Baltiyskaya, 8. Tel.: (495) 6012245. E-mail: nphys@nphys.ru
Sudakov Sergey Konstantinovich, Doctor of Medical Sciences, Professor, Corresponding Member of the Russian Academy of Sciences, Head of P.K. Anokhin Research Institute of Normal Physiology, Moscow.
125315, Moscow, ul. Baltiyskaya, 8. Tel.: (495) 6012245. E-mail: nphys@nphys.ru
