Neurotrophic Factors (BDNF and GDNF) and the Serotonergic System of the Brain.

Neurotrophic factors play a key role in development, differentiation, synaptogenesis, and survival of neurons in the brain as well as in the process of their adaptation to external influences. The serotonergic (5-HT) system is another major factor in the development and neuroplasticity of the brain. In the present review, the results of our own research as well as data provided in the corresponding literature on the interaction of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) with the 5-HT-system of the brain are considered. Attention is given to comparison of BDNF and GDNF, the latter belonging to a different family of neurotrophic factors and being mainly considered as a dopaminergic system controller. Data cited in this review show that: (i) BDNF and GDNF interact with the 5-HT-system of the brain through feedback mechanisms engaged in autoregulation of the complex involving 5-HT-system and neurotrophic factors; (ii) GDNF, as well as BDNF, stimulates the growth of 5-HT neurons and affects the expression of key genes of the brain 5-HT-system - those coding tryptophan hydroxylase-2 and 5-HT1A and 5-HT2A receptors. In turn, 5-HT affects the expression of genes that control BDNF and GDNF in brain structures; (iii) the difference between BDNF and GDNF is manifested in different levels and relative distribution of expression of these factors in brain structures (BDNF expression is highest in hippocampus and cortex, GDNF expression in the striatum), in varying reaction of 5-HT2A receptors on BDNF and GDNF administration, and in different effects on certain types of behavior.

Effect of microgravity on glial cell line-derived neurotrophic factor and cerebral dopamine neurotrophic factor gene expression in the mouse brain.

UNLABELLED: Mice were exposed to 1 month of space flight on the Russian biosatellite BION-M1 to determine its effect on the expression of genes involved in the maintenance of the mouse brain dopamine system. The current article focuses on the genes encoding glial cell line-derived neurotrophic factor (GDNF) and cerebral dopamine neurotrophic factor (CDNF). Space flight reduced expression of the GDNF gene in the striatum and hypothalamus but increased it in the frontal cortex and raphe nuclei area. At the same time, actual space flight reduced expression of the gene encoding CDNF in the substantia nigra but increased it in the raphe nuclei area. To separate the effects of space flight from environmental stress contribution, we analyzed expression of the investigated genes in mice housed for 1 month on Earth in the same shuttle cabins that were used for space flight and in mice of the vivarium control group. Shuttle cabin housing failed to alter the expression of the GDNF and CDNF genes in the brain structures investigated. Thus, actual long-term space flight produced dysregulation in genetic control of GDNF and CDNF genes. These changes may be related to downregulation of the dopamine system after space flight, which we have shown earlier. © 2015 Wiley Periodicals, Inc. SIGNIFICANCE: Our results provide the first evidence of microgravity effects on expression of the GDNF and CDNF neurotrophic factor genes. A considerable decrease in mRNA level of GDNF and CDNF in the nigrostriatal dopamine system was found. Because both GDNF and CDNF play a significant role in maintenance and survival of brain dopaminergic neurons, we can assume that this dysregulation in genetic control of GDNF and CDNF genes in substantia nigra could be among the reasons for the deleterious effects of space flight on the dopamine system.

[Comparison of behavioral effects of fluoxetine, imipramine and new psychotropic drug TC-2153 on mice with hereditary predisposition to catalepsy].

Behavioral effects of classic antidepressants, fluoxetine and imipramine, and new psychotropic benzopentathiepin TC-2153 (20 mg/kg, per os) were studied on mice differing in the predisposition to catalepsy-noncataleptic AKR strain and cataleptic strains CBA and AKR.CBA-D13Mit76 (D13). Mice of D13 strain was created by transferring the CBA-allele of major locus of catalepsy to AKR genome. In the forced swim test (FST) fluoxetine showed antidepressant effect on mice of all three strains, imipramine was effective only in D13 mice, while TC-2153 produced antidepressant effect on AKR and D13 mice. Unlike to imipramine and fluoxetine, TC-2153 did not produce negative side effects in the open field and elevated plus-maze tests. Thus, TC-2153 produces antidepressant effects similar to imipramine and fluoxetine, without any visible negative side effect on locomotory activity and anxiety. The D13 mice in the FST showed high sensitivity to the studied drugs in comparison to the parent strains and can be used as new genetic model for investigation of the mechanism of antidepressant effects.

[Il6st gene mRNA and gp130 protein distribution in the brain structures in mice differing in exagerrated freezing reaction (catalepsy)].

Glycoprotein gp130 is involved in the intracellular transduction of signals from receptors ofinterleukin-6--related cytokines. The linkage between Il6st gene encoding gp130 and predisposition to excessive freezing (catalepsy) in mice was shown. The aim of present study was to investigate the Il6st mRNA concentration, the level and the rate of glycosilation of gp130 in five brain structures in catalepsy-resistant AKR/J mice strain and in catalepsy-prone CBA/LacJ, AKR.CBA-D13Mit76 with the CBA-derived Il6st gene variant in the AKR/J genome, and ASC created by selection of back-crosses between CBA and AKR strains on catalepsy. Highest concentrations of the nonglycosilated and the glycosilated gp130 protein levels were detected in the midbrain. High levels of Il6st mRNA were discovered in the midbrain, the striatum and the hypothalamus in all mouse strains. The level of Il6st mRNA in the striatum of AKR.CBA-D13Mit76 mice was significantly higher compared with AKR/J. An association between hereditary catalepsy and Il6st expression in the striatum in mice was suggested.

[Aggression and acoustic startle response in adult and infant rats with genetically defined aggression towards man and its absence].

The aim of the current study was to investigate the association between expression of acoustic startle response and fear-induced aggression. The intensity of aggressive response towards man and acoustic startle response in adult and 15-day old Norway rats selectively bred for 70 generation for high level or the lack of fear-induced aggression was studied. Adult rats of aggressive strain demonstrated high aggression and increased amplitude of acoustic startle response compared to rats selectively bred for the lack of fear-induced aggression. It was found that, in contrast to infant rats of tame strain, 15-day old rat pups of aggressive strain demonstrated distinct aggressive response towards man, although this response was not as intensive as in adult rats of this strain. There was no considerable difference between aggressive and tame infants in amplitude of acoustic startle response. Significant habituation of startle response was shown in adult rats of aggressive strain, whereas in 15-day old rat pups of aggressive rat strain amplitude of startle response remained unaltered. Both adult and infant rats of tame strain demonstrated considerable habituation of startle response. Thus, defensive aggression in rats with genetic predisposition to fear-induced aggression appears quite early--at eyes opening they demonstrate a pronounced aggressive response toward man. The acoustic startle reflex is one of the elements of complex behavior--fear-induced aggression, and this element is involved in the enhancement of aggressive response towards man in adult rats but does not play any essential role in infant aggressiveness.

[Effect of GDNF on the behavior of ASC mice with high hereditary predisposition to catalepsy].

ASC mice, which were selected for high predisposition to catalepsy, are convenient genetic model for research of central mechanisms related to disorder of motor regulation. The aim of the work was to study the effect of glial cell line-derived neurotrophic factor (GDNF) on catalepsy, locomotor activity, stereotyping behavior in the marble burying test and on the dopamine level in striatum of ASC mice. It was shown that GDNF increased the locomotor activity in the open field, reduced catalepsy expression and stimulated the stereotyping obsessive-compulsive behavior. These changes in behavior were accompanied by increasing dopamine level in striatum.

[Implication of 5-HT2A receptors in the genetic mechanisms of the brain 5-HT system autoregulation].

Brain serotonin (5-HT) system has been implicated in pathophysiology of anxiety, depression, drug addiction, and schizophrenia. 5-HT2A receptor is involved in the mechanisms of stress-induced psychopathology and impulsive behavior. Here, we investigated the role of 5-HT2A receptor in the autoregulation of the brain 5-HT system. The chronic treatment with agonist of 5-HT2A receptor DOI (1.0 mg/kg, i.p./14 days) produced considerable decrease of 5-HT2A receptor-mediated "head-twitches" in AKR/J mice indicating desensitization of 5-HT2A receptors. Chronic DOI treatment failed to alter 5-HT2A receptor gene expression in the midbrain, hippocampus and frontal cortex. At the same time, the increase in the expression of the gene encoding key enzyme of 5-HT synthesis, tryptophan hydroxylase 2 (TPH2), the increase in TPH2 activity and 5-HT levels and decreased expression of serotonin transporter (5-HTT) gene was found in the midbrain of DOI-treated mice. The results provide new evidence of receptor-gene cross-talk in the brain 5-HT system and the implication of 5-HT2A receptor in the autoregulation of the brain 5-HT system.

[Effect of new potential psychotropic drug, 8-(trifluoromethyl)-1,2,3,4,5-benzopentathiepin-6-amine hydrochloride, on the expression of serotonin-related genes in mouse brain].

Study of molecular mechanisms of psychotropic drug action is the main aim of molecular psychopharmacology. New synthetic analog of variacin 8-(Trifluoromethyl)-1,2,3,4,5-benzopentathiepin-6-amine (TX-2153) was shown to produce anxiolytic and anticonvulsant effects on mice. Here the effect of chronic administration of TX-2153 on expression of some serotonin-related genes in mouse brain was investigated. The drug (10 mg/kg, per os, 16 days) was administered to adult males of ASC (Antidepressant Sensitive Catalepsy) mouse strain characterizing by alterations in behavior and brain serotonin system. The expression of genes encoding 1) the key enzyme of serotonin synthesis, tryptophan hydroxylase 2 (TPH2), 2) main enzyme of serotonin degradation, monoamine oxydase A (MAOA), 3) 5-HT transporter (SERT) and 4) 5-HT(1A) receptor was studied using quantitative RT-PCR. TX-2153 significantly reduced m-RNA level of 5-HT(1A) receptor and MAOA genes in the midbrain without any effect on expression of these genes in the frontal cortex and hippocampus. The drug failed to affect expression of TPH2 and SERT genes in the midbrain. The result indicates involvement of the brain 5-HT system in the molecular mechanism underlying the effect of TX-2153.

[The role of the glycoprotein gp130 in serotonin mediator system in mouse brain].

Glycoprotein gp130 is involved in signaling out of significant cytokine receptors as interleukin-6 (IL-6), leukemia inhibitory factor and ciliary neurotrophic factor, which play critical role in immunity, inflammation and neurogenesis. IL-6 and brain neurotransmitter serotonin are involved in the mechanism of depression. The aim of this work was to investigat the role of protein gp130 in the regulation of expression of genes, coding the key enzyme of serotonin synthesis--tryptophan hydroxylase 2 (TPH2), 5-HT-transporter, 5-HT(1A)- and 5-HT(2A)-receptors of serotonin. The study was carried out on adult mouse males of AKR and congenic AKR.CBA-D13Mit76 strains, created by transfer of the fragment of chromosome 13 containing the gene coding gp130 protein from CBA/Lac strain to the genome of AKR/J strain. Decreased expression of 5-HT(1A) - 5-HT(2A)-receptor genes in hippocampus midbrain and TPH2 gene in midbrain in AKR.CBA-D13Mit76 mice compared with AKR mice were shown. Activation of nonspecific immunity by bacterial endotoxin lipopolysaccharide (LPS) administration did not affect the genes expression in AKR mice, but increased 5-HT(2A)-receptor expression in midbrain and decreased 5-HT(1A)-receptor expression in cortex in AKR.CBA-D13Mit76 mice. The results indicate: 1) the participation of gp130 in the regulation of TPH2, 5-HT(1A)- and 5-HT(2A)-receptor genes and 2) association of this protein in the genetically determined sensitivity to LPS.

[Effects of chronic imipramine treatment on behavior in mice of congenic strains AKR and AKR.CBA-D13Mit76 differing in the distal fragment of chromosome 13].

Congenic mouse strain AKR.CBA-D13Mit76 carries the 59-70 cM fragment of chromosome 13 transferred from genome of cataleptic CBA/Lac strain to genome of AKR/J none-cataleptic strain. This fragment contains the major gene of predisposition to pinch-induced catalepsy. We investigated contribution of the fragment to regulation of sensitivity of catalepsy, sexual motivation and social investigation to classical tricyclic antidepressant imipramine. The sexual motivation was higher in AKR.CBA-D13Mit76 than in AKR mice. Chronic imipramine treatment (25 mg/kg) reduced it in AKR.CBA-D13Mit76 mice and had no effect on weakly expressed sexual motivation of AKR males. No significant effects of genotype or chronic imipramine treatment on characteristics of social interest were observed. Imipramine failed to alter catalepsy expression in AKR.CBA-DI3Mit76 mice. Possible molecular genetic mechanisms underlying difference in behavioral responses to antidepressant administration are discussed.

[Effect of genotype and emotional stress on hygienic grooming in inbred mice].

Body care behavior (grooming) is an adaptation aimed at removing litter particles, pathogenic microbes and parasites from animal fur and skin. Moreover, it serves as an indicator of animal health. It was observed that chronic stress suppressed fur cleaning. In this article, a technique of direct measurement of fur cleaning using the cleaning dynamics of a fluorescent spot applied on animal's back is described. Significant effects of genotype and emotional stress on the dynamics of fur cleaning are shown. Mice of C57BL/6, CBA and CC57BR strains clean green fluorescent spot rapidly (1-2 h) whereas animals of AKR strain clean it slowly (up to 24 h). Behavioral restriction for 30 min substantially reduced fur cleaning in AKR, CBA and CC57BR, but not in C57BL/6. The stress-induced attenuation of Hygienic grooming is a new index of sensitivity (resistance) to stress.

Intracerebral administration of brain-derived neurotrophic factor (BDNF) reduces severity of cataleptic freezing in mice with genetic predisposition to catalepsy.

Single administration of brain-derived neurotrophic factor (BDNF) into the lateral ventricle of ASC mice (Antidepressant Sensitive Catalepsy), a model of depression-like state, significantly decreased predisposition to cataleptic freezing in these animals. These findings indicate that BDNF can appear as a promising antidepressant of new generation and that ASC mice can be used as an adequate model for investigations of the mechanisms of behavior modification by BDNF.

Effect of mouse chromosome 13 terminal fragment on liability to catalepsy and expression of tryptophane hydroxylase-2, serotonin transporter, and 5-HT1A receptor genes in the brain.

Congenic mice obtained by genome fragments transfer from one strain to another are a potent tool for studies of the molecular mechanisms of behavioral mutations. The 59-70 cM fragment of chromosome 13 containing the locus determining predisposition to freezing reaction (catalepsy) and the gene encoding 5-HT(1A) receptor were transferred from cataleptic CBA/Lac mice into the genome of catalepsy-resistant AKR/J mice. The impact of this fragment for the severity of catalepsy and expression of genes encoding tryptophane hydroxylase-2, serotonin transporter, and 5-HT(1A) receptor was studied. Half of mice of the resultant congenic AKR.CBA-D13Mit76 strain exhibited pronounced catalepsy, similarly to donor CBA animals. The expression of 5-HT(1A) receptor gene in the midbrain of AKR animals was significantly higher than in CBA. The level of 5-HT(1A) receptor mRNA in AKR.CBA-D13Mit76 animals was significantly higher than in the donor strain. Mice of parental AKR and CBA strains did not differ from each other and from AKR.CBA-D13Mit76 animals by the levels of tryptophane hydroxylase-2 and serotonin transporter genes mRNA. These data prove the location of catalepsy regulating gene in the distal fragment of chromosome 13. The recipient strain genome enhanced the expression of 5-HT(1A) receptor gene in the brain without modulating the expression of catalepsy gene.

[Immobility and hyperthermia in tail suspension test: the association with Porsolt test and startle response in 11 inbred mouse strains, and the effect of MAO A knockout].

The tail suspension test (TST)-induced immobility and hyperthermia and acoustic startle response were studied in 11 mouse inbred strains and in MAO A knockout Tg8 mice. Significant genotypic differences in TST-induced immobility rather than hyperthermia and the lack of correlation between the expression of immobility and hyperthermia were found. Positive genotypic correlation between immobility in the TST and Porsolt test as well as TST-induced immobility and acoustic startle response was shown. Genetic knockout of the main enzyme in serotonin and catecholamines metabolism, MAO A, decreased the startle response and TST-induced hyperthermia but had no effect on TST-induced immobility in Tg8 mice indicating the differences in neurochemical regulation of these TST-induced responses. The results support the validity of the TST as dry-land version of the forced swimming test and draw attention to TST-induced hyperthermia as an animal model of response to uncontrollable, inescapable stress demonstrated in humans.

[Effects of chronic fluoxetine treatment on catalepsy and immune response in mice genetically predisposed to freezing reaction: the role of 5-HT1A and 5-HT2A receptors and tph2 and SERT genes].

ASC/Icg (Antidepressant Sensitive Catalepsy) mouse strain selected for high predisposition to pinch-induced catalepsy is characterized by depressive-like behavior and impaired immune response. Chronic treatment with SSRI fluoxetine attenuated catalepsy manifestation and normalized a decreased number of rosette-forming cells (RFC) in spleen in ASC mice. Chronic fluoxetine administration had no effect on catalepsy and RFC number in mice of parental cataleptic CBA/Lac strain. Fluoxetine failed to alter 5-HT1A receptor functional activity in mice of both strains and diminished 5-HT2A receptor functional activity in CBA but not in ASC mice. No effect on cortical 5-HT1A and 5-HT2A receptor mRNA levels and on 5-HT1A receptor, tph2 (tryptophan hydroxylase-2) and SERT (serotonin transporter) mesencephalic gene expression was observed in ASC mice. Other possible serotonergic mechanisms of fluoxetine effect on catalepsy and immune response in mice with depressive-like state are discussed.

From gene to aggressive behavior: the role of brain serotonin.

This article addresses a question at the juncture of neurophysiology and neurogenetics--the role of the brain neurotransmitter serotonin in the genetic control of behavior. Published data are presented, along with results obtained from studies performed at the Behavioral Neurogenomics Laboratory. The role of protein elements of the brain serotonin system (key enzymes in serotonin metabolism and serotonin 5-HT(1A) receptors), which are subject to the direct influence of genes, in the genetic predisposition to aggressive behavior is discussed. Experimental results obtained in Norwegian rats selected over more than 50 generations for the absence of aggressivity and for high aggressivity to humans are presented, along with data from experiments on mouse lines and mice with genetic knockout of MAO A. These data provide evidence that 1) brain serotonin makes a significant contribution to the mechanisms underlying genetically determined individual differences in aggressivity, and 2) the genes encoding the main enzymes of serotonin metabolism in the brain (tryptophan hydroxylase-1 and MAO A) and the 5-HT(1A) receptor are members of a set of genes modulating aggressive behavior.

[Chronic effect of thyroxine on behavior and brain serotonin receptors in mice with the sharp difference in predisposition to catalepsy].

Effects of chronic thyroxine treatment (2mg/l, 60 days) on catalepsy, functional activity and expression of 5-HT(1A) and 5-HT(2A) receptors genes in the brain were studied in adult males of catalepsy-prone ASC and catalepsy-resistant AKR mouse strains. Thyroxine caused an appearance of cataleptics in AKR, but produced an anticataleptic effect on ASC mice. Chronic thyroxine treatment increased the functional activity and expression of 5-HT(2A) receptors in the frontal cortex in AKR, but not in ASC mice. Hormone markedly attenuated hypothermic effect of 8-OH-DPAT, 5-HT(1A) receptor agonist, but did not affect the expression of 5-HT(1A) receptors in ASC mice. The results suggest the involvement of the 5-HT(2A) receptors in the cataleptogenic and the 5-HT(1A) receptors in the anticataleptic effects of hormone.

Involvement of brain serotonin 5-HT1A receptors in genetic predisposition to aggressive behavior.

Experiments were performed on Norwegian rats selected over more than 59 generations for high and low levels of high-affective defensive aggressivity and on highly aggressive (offensive) Tg8 mice with irreversible monoamine oxidase A knockout. There were significant differences in the functional state and expression of 5-HT(1A) receptors between highly aggressive and non-aggressive animals. Functional activity assessed in terms of hypothermia evoked by a 5-HT(1A) agonist was significantly greater in non-aggressive rats and mice than in aggressive animals. The high level of functional activity in non-aggressive rats coincided with a greater level of expression of 5-HT(1A) receptors in the midbrain. The level of 5-HT(1A) receptor mRNA in aggressive mice was unchanged in the midbrain and hypothalamus and was increased in the frontal cortex and amygdaloid complex. These results led to the conclusion that 5-HT(1A) receptors play a significant role in the mechanisms of genetic predisposition to aggressive behavior.

[The C1473G polymorphism in gene tph2 is the main factor mediating the genetically defined variability of tryptophan hydroxylase-2 activity in the mouse brain].

Brain neurotransmitter serotonin is involved in the regulation of many physiological functions and types of behavior. The key enzyme of serotonin synthesis in the brain is tryptophan hydroxylase-2 (TPH-2). An association of the C1473G polymorphism in gene tph2 causing the replacement of Pro447 by Arg447 in TPH-2 molecule with enzyme activity in the mouse brain of 10 inbred strains was found. Association of the polymorphism with the TPH-2 activity in the brain of F2 hybrids between strains C57BL/6 and CC57BR was shown. The results indicate that the C1473G polymorphism in gene tph2 is the main factor determining the genetic defined variability of enzyme activity in the mouse brain.

[High predisposition to catalepsy decreases intermale aggression and increases acoustic startle reflex amplitude].

Reaction of freezing (a pronounced motor inhibition, catalepsy) is suggested to be associated with fear in response to predator appearance or attack of aggressive congener. In order to evaluate association between a kind of behavior such as freezing, aggressiveness and fear, the effects of high predisposition to catalepsy on intermale aggression, acoustic startle response and anxiety-related behavior in the light/dark test were studied. Mice of 14th and 15th generations of selective breeding for high predisposition to catalepsy were characterized by a significant decrease in aggressive behavior. The marked decrease in the percentage of aggressive mice in the catalepsy-prone strain is consistent with the notion that aggression and catalepsy represent two alternative kinds of behavior in intermale conflicts. A positive correlation was found between high predisposition to catalepsy and startle reflex amplitude (but not anxiety-related behavior).