Dmitry A. Smagin

Extended effect of chronic social defeat stress in childhood on behaviors in adulthood

Individuals exposed to social stress in childhood are more predisposed to developing psychoemotional disorders in adulthood. Here we use an animal model to determine the influence of hostile social environment in adolescence on behavior during adult life. One-month-old adolescent male mice were placed for 2 weeks in a common cage with an adult aggressive male. Animals were separated by a transparent perforated partition, but the adolescent male was exposed daily to short attacks from the adult male. After exposure to social stress, some of the adolescent mice were placed for 3 weeks in comfortable conditions. Following this rest period, stressed young males and adult males were studied in a range of behavioral tests to evaluate the levels of anxiety, depressiveness, and communicativeness with an unfamiliar partner. In addition, adult mice exposed to social stress in adolescence were engaged in agonistic interactions. We found that 2 weeks of social stress result in a decrease of communicativeness in the home cage and diminished social interactions on the novel territory. Stressed adolescents demonstrated a high level of anxiety in the elevated plus-maze test and helplessness in the Porsolt test. Furthermore, the number of dividing (BrdU-positive) cells in the subgranular zone of the dentate gyrus was significantly lower in stressed adolescents. After 3 weeks of rest, most behavioral characteristics in different tests, as well as the number of BrdU-positive cells in the hippocampus, did not differ from those of the respective control mice. However, the level of anxiety remained high in adult males exposed to chronic social stress in childhood. Furthermore, these males were more aggressive in the agonistic interactions. Thus, hostile social environment in adolescence disturbs psychoemotional state and social behaviors of animals in adult life.

Repeated positive fighting experience in male inbred mice

Repeated aggression is a frequent symptom of many psychiatric and neurological disorders, including obsessive-compulsive and attention deficit hyperactivity disorders, bipolar and post-traumatic stress disorders, epilepsy, autism, schizophrenia and drug abuse. However, repeated aggression is insufficiently studied because there is a lack of adequate models in animals. The sensory contact model (SCM), widely used to study the effects of chronic social defeat stress, can also be used to investigate the effects of repeated aggression. Mice with repeated positive fighting experience in daily agonistic interactions in this model develop pronounced aggressiveness, anxiety and impulsivity, disturbances in motivated and cognitive behaviors, and impairments of sociability; they also demonstrate hyperactivity, attention-deficit behavior, motor dysfunctions and repetitive stereotyped behaviors, such as jerks, rotations and head twitches. In this protocol, we describe how to apply the SCM to study repeated aggression in mice. Severe neuropathology develops in male mice after 20–21 d of agonistic interactions.

Altered Hippocampal Neurogenesis and Amygdalar Neuronal Activity in Adult Mice with Repeated Experience of Aggression

Repeated experience of winning in a social conflict setting elevates levels of aggression and may lead to violent behavioral patterns. Here, we use a paradigm of repeated aggression and fighting deprivation to examine changes in behavior, neurogenesis, and neuronal activity in mice with positive fighting experience. We show that for males, repeated positive fighting experience induces persistent demonstration of aggression and stereotypic behaviors in daily agonistic interactions, enhances aggressive motivation, and elevates levels of anxiety. When winning males are deprived of opportunities to engage in further fights, they demonstrate increased levels of aggressiveness. Positive fighting experience results in increased levels of progenitor cell proliferation and production of young neurons in the hippocampus. This increase is not diminished after a fighting deprivation period. Furthermore, repeated winning experience decreases the number of activated (c-fos-positive) cells in the basolateral amygdala and increases the number of activated cells in the hippocampus; a subsequent no-fight period restores the number of c-fos-positive cells. Our results indicate that extended positive fighting experience in a social conflict heightens aggression, increases proliferation of neuronal progenitors and production of young neurons in the hippocampus, and decreases neuronal activity in the amygdala; these changes can be modified by depriving the winners of the opportunity for further fights.

Dysfunction in Ribosomal Gene Expression in the Hypothalamus and Hippocampus following Chronic Social Defeat Stress in Male Mice as Revealed by RNA-Seq

Chronic social defeat stress leads to the development of anxiety- and depression-like states in male mice and is accompanied by numerous molecular changes in brain. The influence of 21-day period of social stress on ribosomal gene expression in five brain regions was studied using the RNA-Seq database. Most Rps, Rpl, Mprs, and Mprl genes were upregulated in the hypothalamus and downregulated in the hippocampus, which may indicate ribosomal dysfunction following chronic social defeat stress. There were no differentially expressed ribosomal genes in the ventral tegmental area, midbrain raphe nuclei, or striatum. This approach may be used to identify a pharmacological treatment of ribosome biogenesis abnormalities in the brain of patients with “ribosomopathies.”

Heterogeneity of Brain Ribosomal Genes Expression Following Positive Fighting Experience in Male Mice as Revealed by RNA-Seq

Repeated positive fighting experience in daily agonistic interactions is accompanied by changes of brain neurotransmitter activity and genes’ expression in male mice. This paper is focused on the analysis of ribosomal genes expression data as revealed by whole-transcriptome analysis (RNA-Seq) in five brain regions of male mice with long repeated experience of aggression accompanied by wins (winners). Downregulation of most Rps, Rpl, Mrps, and Mrpl genes was found in the midbrain raphe nuclei and striatum and upregulation—in the hippocampus and hypothalamus of the winners. There were no changes in ribosomal gene expression in the ventral tegmental area. The data allow considering the alteration in ribosomal gene expression as an animal model of ribosomal dysfunction developed under positive fighting experience in male mice.

RNA-Seq Mouse Brain Regions Expression Data Analysis: Focus on ApoE Functional Network.

Abstract ApoE expression status was proved to be a highly specific marker of energy metabolism rate in the brain. Along with its neighbor, Translocase of Outer Mitochondrial Membrane 40 kDa (TOMM40) which is involved in mitochondrial metabolism, the corresponding genomic region constitutes the neuroenergetic hotspot. Using RNA-Seq data from a murine model of chronic stress a significant positive expression coordination of seven neighboring genes in ApoE locus in five brain regions was observed. ApoE maintains one of the highest absolute expression values genome-wide, implying that ApoE can be the driver of the neighboring gene expression alteration observed under stressful loads. Notably, we revealed the highly statistically significant increase of ApoE expression in the hypothalamus of chronically aggressive (FDR < 0.007) and defeated (FDR < 0.001) mice compared to the control. Correlation analysis revealed a close association of ApoE and proopiomelanocortin (Pomc) gene expression profiles implying the putative neuroendocrine stress response background of ApoE expression elevation therein.

Aberrant expression of collagen family genes in the brain regions developing under agonistic interactions in male mice

As previously established, chronic agonistic interactions lead to the development of depression-like state under social defeat stress in the defeated mice and pathology of aggressive behavior in the winning mice. According to the numerous research data, these psychopathological states are accompanied by tremendous molecular and cellular changes in the brain. The paper aimed to study the influence of 20-day period of agonistic interactions on the expression mode of collagen family genes, encoding the proteins, which are basic components of extracellular matrix (ECM), in the different brain regions of mice using the RNA-Seq database. Most of the differentially expressed collagen genes were upregulated in the hypothalamus and striatum of chronically aggressive and defeated mice and in the hippocampus of the defeated mice. In the ventral tegmental area the most genes were downregulated in both experimental groups. It has been assumed that aberrant expression of collagen genes induced by long experience of agonistic interactions can indicate defects of ECM specific for brain regions in mice with alternative social experiences. This study first shows remodeling of molecular base in the ECM under development of experimental psychoneuropathologies. Corresponding authors: Kudryavtseva N.N., n.n.kudryavtseva@gmail.com; Babenko V.N., bob@bionet.nsc.ru

Abnormal Social Behaviors and Dysfunction of Autism-Related Genes Associated With Daily Agonistic Interactions in Mice

Abstract Decline in socialization and communication may be the result of negative social environment, but it can also be due to other environmental as well as genetic factors, leading to the development of affective or neurological disorders, including autistic spectrum disorders. Animal models have been employed to study such disorders. In this chapter, we present a single experimental study as an example. We wish to demonstrate how one can utilize environmental manipulation methods, including social defeat induced stress, to explore behavioral and gene expression changes as a model of abnormal social behavior. In our example, we induced changes in social behaviors by providing repeated experience with social defeat and aggression during daily agonistic interactions in male mice. In addition, we also studied potential alterations in the expression of genes in five brain regions. Analysis of an RNA-Seq database of the whole transcriptome revealed changes in expression of the Tph2 , Maoa , Slc6a4 , Htr7 , Gabrb3 , Nrxn1 , Nrxn2 , Nlgn1 , Nlgn2 , Nlgn3 , Shank2 , Shank3 , Fmr1 , Ube3a , Pten , Cntn3 , Foxp2 , Oxtr , Reln , Cadps2 , Pcdh10 , Ctnnd2 , En2 , Arx , Auts2 , Mecp2 , and Ptchd1 genes. These genes have also been associated with autism in humans. Our research thus demonstrates for the first time that abnormalities in social behaviors induced by negative social environment in adult mice are associated with altered expression of autism-related genes in the brain. We argue that environmental manipulations may thus represent a potential way the human central nervous system disorders associated with abnormal social behavior could be modeled and analyzed.

Changes in the Expression of Neurotransmitter System Genes in the Ventral Tegmental Area in Depressed Mice: RNA-SEQ Data

Chronic social stress leads to the development of mixed anxious/depressive disorders in male mice, similar to those in humans. Changes in the functioning of many neurotransmitter systems have been shown to occur in the brains of depressed animals. The aim of the present work was to study the expression genes encoding proteins involved in the metabolism, transport, and reception of serotonin, catecholamines, glutamate, and GABA in the ventral tegmental area of the brain – an area playing an important role in regulating motivations and emotions and involved in the mechanisms underlying the development of affective disorders. Mixed anxious/depressive disorder in animals was formed by chronic social stress for 20 days. Samples of ventral tegmental area were sequenced at Genoanalytica (http://genoanalytica.ru/, Moscow, Russia). Expression of the serotoninergic genes Tph2, Maob, Htr4, Htr1a, and Slc6a4 was increased in depressed animals, while expression of the Htr3a gene was decreased. The expression of the dopaminergic genes Th, Ddc, Slc6a3, Slc18a2, Drd2, and Maob was increased and the expression of the noradrenergic genes Dbh, Slc6a2, Adra2c, and Adra2a was decreased. Expression of the GABAergic genes Gabra1, Gabra2, Gabrg2, Gabrg1, Gabrq, Gad1, and Gad2 and the glutamatergic genes Gria1, Gria2, Grik2, Grm2, Grm5, and Slc17a8b was greater in depressed animals than controls. Formation of mixed anxious/depressive disorder in response to chronic social stress in mice led to increases in the expression of genes encoding proteins involved in the operation of the serotoninergic, dopaminergic, glutamatergic, and GABAergic systems, while expression of genes responsible for adrenergic reception decreased. It is suggested that a key role in the synchronous changes in the expression of genes for different neurotransmitter systems may be played by the Drd2 and Htr3a genes.

Interaction of Depression and Anxiety in the Development of Mixed Anxiety/Depression Disorder. Experimental Studies of the Mechanisms of Comorbidity (review)

The symptoms of depression and anxiety often accompany each other. This is apparent both in clinical practice and in laboratory studies. The combination of anxiety and depression in humans responds more slowly to treatment, requires higher doses of drugs, and increases the probability of suicide and the frequency of recurrences. In addition, existing antidepressants and anxiolytics exert their therapeutic effects even in the monopolar development of anxiety or depression in only a limited number of cases. This review of the literature and our own data analyzes the relationship between anxiety and depression. Psychotropic drugs with different spectra of action in a model of mixed anxiety/depression disorder induced by chronic social stress in male mice showed that the states of anxiety and depression change independently in response to anxiolytics and antidepressants.