D. V. Bazovkina

Genetic structure of hereditary catalepsy in mice.

Catalepsy or pronounced freezing is a natural passive defense strategy in animals and a syndrome of some mental disorders in human. Hereditary catalepsy was shown to be associated with depressive‐like features in rats and mice. The loci underlying the difference in predisposition to catalepsy between catalepsy‐prone CBA/lacJ and catalepsy‐resistant AKR/J mice were mapped using congenic line and selective breeding approaches. Three congenic mouse lines (AKR.CBA‐D13Mit76C, AKR.CBA‐D13Mit76A and AKR.CBA‐D13Mit78) carrying the 59‐ to 70‐, 61‐ to 70‐ and 71‐ to 75‐cm fragments of chromosome 13 transferred from the CBA to the AKR genome were created by nine successive backcrossing of (CBA × AKR)F1 on AKR strain. Because catalepsy was found only in the AKR.CBA‐D13Mit76C and AKR.CBA‐D13Mit76A mice, the major gene of catalepsy was mapped on the fragment of 61–70 cm. Selective breeding of the (CBA × (CBA × AKR))BC backcross generation for high predisposition to catalepsy showed numerous genome‐wide distributed CBA‐derived alleles as well as the AKR‐derived alleles mapped on chromosome 17 and on the proximal parts of chromosomes 10 and 19 that increased the cataleptogenic effect of the major gene.

Selective breeding for catalepsy changes the distribution of microsatellite D13Mit76 alleles linked to the 5-HT1A serotonin receptor gene in mice

Catalepsy (pronounced motor inhibition) is a natural defensive reaction against predator. Recently, the quantitative trait locus for catalepsy was mapped on mouse chromosome 13 near the 5‐HT1A serotonin receptor gene. Here, the linkage between catalepsy and the 5‐HT1A receptor gene was verified using breeding experiment. Selective breeding for high predisposition to catalepsy was started from backcross BC[CBA × (CBA × AKR)] generation between catalepsy‐prone (CBA) and catalepsy‐resistant (AKR) mouse strains. CBA and AKR strains also differed in the 5‐HT1A receptor functional activity. A rapid increase of cataleptic percentage from 21.2% in the backcrosses to 71% in the third generation of selective breeding (S3) was shown. The fragment of chromosome 13 including the 5‐HT1A receptor gene was marked with D13Mit76 microsatellite. Breeding for catalepsy increased the concentration of CBA‐derived and decreased the concentration of AKR‐derived alleles of microsatellite D13Mit76 in the S1 and S2. All mice of the S9 and S12 were homozygous for CBA‐derived allele of D13Mit76 marker. Mice of the S12 showed CBA‐like receptor activity. These findings indicate that selective breeding for behavior can involve selection of polymorphic variants of the 5‐HT1A receptor gene.

The role of 5-HT2A receptor and 5-HT2A/5-HT1A receptor interaction in the suppression of catalepsy.

In the present study, the 5‐HT2A and 5‐HT1A receptors functional activity and 5‐HT2A receptor gene expression were examined in the brain of ASC/Icg and congenic AKR.CBAD13Mit76C mouse strains (genetically predisposed to catalepsy) in comparison with the parental catalepsy‐resistant AKR/J and catalepsy‐prone CBA/Lac mouse strains. The significantly reduced 5‐HT2A receptor functional activity along with decreased 5‐HT2A receptor gene expression in the frontal cortex was found in all mice predisposed to catalepsy compared with catalepsy‐resistant AKR/J. 5‐HT2A agonist DOI (0.5 and 1 mg/kg, i.p.) significantly reduced catalepsy in ASC/Icg and CBA/Lac, but not in AKR.CBAD13Mit76C mice. Essential increase in 5‐HT1A receptor functional activity was shown in catalepsy‐prone mouse strains in comparison with catalepsy‐resistant AKR/J mice. However, in AKR.CBAD13Mit76C mice it was lower than in ASC/Icg and CBA/Lac mice. The inter‐relation between 5‐HT2A and 5‐HT1A receptors in the regulation of catalepsy was suggested. This suggestion was confirmed by prevention of DOI anticataleptic effect in ASC/Icg and CBA/Lac mice by pretreatment with 5‐HT1A receptor antagonist p‐MPPI (3 mg/kg, i.p.). At the same time, the activation of 5‐HT2A receptor led to the essential suppression of 5‐HT1A receptor functional activity, indicating the opposite effect of 5‐HT2A receptor on pre‐ and postsynaptic 5‐HT1A receptors. Thus, 5‐HT2A/5‐HT1A receptor interaction in the mechanism of catalepsy suppression in mice was shown.

Selection for the Predisposition to Catalepsy Enhances Depressive-like Traits in Mice

Immobility reaction or catalepsy is a natural passive defensive (cryptic) behavioral response to the appearance of a predator. Selection for high predisposition to catalepsy has been performed in a population of (CBA × (CBA × AKR)) backcrosses of the crossing between mouse lines prone and resistant to catalepsy (CBA and AKR, respectively). A rapid increase in the number of animals with catalepsy has been observed: from 23% in backcrosses to 71% in the S3 generation. Selection for catalepsy does not affect mouse anxiety in the open field and plus-maze tests. However, S8 and S9 mice are characterized by a decreased motor activity in the open-field test and an increased immobility in the forced swim and tail suspension tests, which is interpreted as an increase in “ depressiveness.” The results indicate that genetically determined catalepsy is related to depressive-like characteristics of defensive behavior.

Effect of glial cell line-derived neurotrophic factor on behavior and key members of the brain serotonin system in mouse strains genetically predisposed to behavioral disorders.

The effect of glial cell line‐derived neurotrophic factor (GDNF) on behavior and on the serotonin (5‐HT) system of a mouse strain predisposed to depressive‐like behavior, ASC/Icg (Antidepressant Sensitive Cataleptics), in comparison with the parental “nondepressive” CBA/Lac mice was studied. Within 7 days after acute administration, GDNF (800 ng, i.c.v.) decreased cataleptic immobility but increased depressive‐like behavioral traits in both investigated mouse strains and produced anxiolytic effects in ASC mice. The expression of the gene encoding the key enzyme for 5‐HT biosynthesis in the brain, tryptophan hydroxylase‐2 (Tph‐2), and 5‐HT1A receptor gene in the midbrain as well as 5‐HT2A receptor gene in the frontal cortex were increased in GDNF‐treated ASC mice. At the same time, GDNF decreased 5‐HT1A and 5‐HT2A receptor gene expression in the hippocampus of ASC mice. GDNF failed to change Tph2, 5‐HT1A, or 5‐HT2A receptor mRNA levels in CBA mice as well as 5‐HT transporter gene expression and 5‐HT1A and 5‐HT2A receptor functional activity in both investigated mouse strains. The results show 1) a GDNF‐induced increase in the expression of key genes of the brain 5‐HT system, Tph2, 5‐HT1A, and 5‐HT2A receptors, and 2) significant genotype‐dependent differences in the 5‐HT system response to GDNF treatment. The data suggest that genetically defined cross‐talk between neurotrophic factors and the brain 5‐HT system underlies the variability in behavioral response to GDNF.

Effect of imipramine on the behavior and cerebral 5-HT1A serotonin receptors in mice genetically predisposed to catalepsy

Acute injection of imipramine to NPK mice hereditary predisposed to pinching catalepsy reduced immobility in the forced swimming test, but had no effect on catalepsy. Chronic treatment with imipramine reduced the severity of catalepsy and functional activity of 5-HT1A serotonin receptors, but did not modify their expression in the hippocampus. NPK mice can be a convenient model for studies of the effects of antidepressant.

Effects of brain-derived and glial cell line-derived neurotrophic factors on startle response and disrupted prepulse inhibition in mice of DBA/2J inbred strain.

Prepulse inhibition (PPI), the reduction in acoustic startle reflex when it is preceded by weak prepulse stimuli, is a measure of critical to normal brain functioning sensorimotor gating. PPI deficit was shown in a variety of psychiatric disorders including schizophrenia, and in DBA/2J mouse strain. In the current study, we examined the effects of brain-derived (BDNF) and glial cell line-derived (GDNF) neurotrophic factors on acoustic startle response and PPI in DBA/2J mice. It was found that BDNF (300 ng, i.c.v.) significantly increased amplitude of startle response and restored disrupted PPI in 7 days after acute administration. GDNF (800 ng, i.c.v.) did not produce significant alteration neither in amplitude of startle response nor in PPI in DBA/2J mice. The reversal effect of BDNF on PPI deficit was unusually long-lasting: significant increase in PPI was found 1.5 months after single acute BDNF administration. Long-term ameliorative effect BDNF on disrupted PPI suggested the implication of epigenetic mechanism in BDNF action on neurogenesis. BDNF rather than GDNF could be a perspective drug for the treatment of sensorimotor gating impairments.

Hereditary catalepsy in mice is associated with the brain dysmorphology and altered stress response

Catalepsy is a passive defensive strategy in response to threatening stimuli. In exaggerated forms it is associated with brain dysfunctions. The study was aimed to examine (1) possible association of the hereditary catalepsy with neuroanatomical characteristics and (2) sensitivity of the catalepsy expression, HPA and brain serotonin (5-HT) systems to restraint stress (for one hour) in mice of catalepsy-prone (CBA/Lac, ASC (Antidepressant Sensitive Catalepsy), congenic AKR.CBA-D13M76) and catalepsy-resistant (AKR/J) strains. Magnetic resonance imaging showed that the catalepsy-prone mice were characterized by the smaller size of the pituitary gland and the larger size of the thalamus. In ASC mice, diencephalon region (including hypothalamus) and striatum were significantly reduced in size. Restraint stress provoked catalepsy in AKR mice and enhanced it in the catalepsy-prone mice. Stress-induced corticosterone elevation was diminished, while 5-HT metabolism (5-HIAA level or 5-HIAA/5-HT ratio) in the midbrain was significantly augmented by stress in the catalepsy-prone mice. The multivariate factor analysis revealed interactions between the basal levels and the stress-induced alterations of 5-HT metabolism in the hippocampus and midbrain suggesting the interaction between multiple alterations in 5-HT neurotransmission in several brain structures in the regulation of hereditary catalepsy. The study indicated an association between the hereditary catalepsy, neuroanatomical characteristics, and neurochemical responses to emotional stress. The catalepsy-prone genotypes seem to be more susceptible to stress that suggests them as the adequate models to study the genetic predisposition to stress-based neuropathology. The data support the association of hereditary catalepsy with the inherited brain dysfunction of a neurodegenerative nature.

RECEPTOR-GENES CROSS-TALK: EFFECT OF CHRONIC 5-HT1A AGONIST 8-HYDROXY-2-(DI-N-PROPYLAMINO) TETRALIN TREATMENT ON THE EXPRESSION OF KEY GENES IN BRAIN SEROTONIN SYSTEM AND ON BEHAVIOR

Dysfunction in brain serotonin (5-HT) system has been implicated in the psychopathology of anxiety, depression, drug addiction, and schizophrenia. The 5-HT(1A) receptors play a central role in the control of 5-HTergic neurotransmission. There are some scarce data showing cross-regulation between 5-HT receptors. Here, we investigated whether interaction exists between 5-HT(1A) receptor and genes encoding key members in brain 5-HT system. Chronic treatment with selective agonist of 5-HT(1A) receptor 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (1.0 mg/kg i.p., 14 days) produced considerable decrease in hypothermic response to acute administration of 8-OH-DPAT in CBA/Lac mice indicating desensitization of 5-HT(1A) receptors. The decrease in 5-HT(1A) gene expression as well as decrease in the expression of gene encoding key enzyme in 5-HT synthesis, tryptophan hydroxylase-2 (TPH-2) in the midbrain, and the expression of the gene encoding 5-HT(2A) receptor in the frontal cortex was shown. There were no significant changes in 5-HT transporter mRNA level in the midbrain. Despite considerable decrease in the expression of the genes encoding tryptophan hydroxylase-2, 5-HT(1A) and 5-HT(2A) receptors, chronic 8-OH-DPAT treatment failed to produce significant changes in 5-HT(1A)-linked behavior (intermale aggression, open-field behavior, light-dark box, and pinch-induced catalepsy), suggesting compensatory and adaptive effect of genes suppression. The obtained data on the effect of 8-OH-DPAT-induced desensitization of 5-HT(1A) receptors on 5-HT(1A), 5-HT(2A) and TPH-2 gene expression demonstrated the role of 5-HT(1A) receptor as indirect regulator of gene expression. The results provide the first evidence of receptor-key genes interaction in brain 5-HT system and may have profound implications in understanding the functioning of the brain neurotransmitter systems.

Antidepressant-Like Effects of Central BDNF Administration in Mice of Antidepressant Sensitive Catalepsy (ASC) Strain.

Although numerous data evidence the implication of brain-derived neurotrophic factor (BDNF) in the pathophysiology of depression, the potential for BDNF to correct genetically defined depressive-like states is poorly studied. This study was aimed to reveal antidepressant-like effects of BDNF (300 ng, 2×, i.c.v.) on behavior and mRNA expression of genes associated with depression-like state in the brain in mice of antidepressant sensitive catalepsy (ASC) strain characterized by high hereditary predisposition to catalepsy and depressive-like features. Behavioral tests were held on the 7th-16th days after the first (4th-13th after the second) BDNF injection. Results showed that BDNF normalized impaired sexual motivation in the ASC males, and this BDNF effect differed, with advantageous effects, from that of widely used antidepressants. The anticataleptic effect of two BDNF injections was enhanced compared with a single administration. A tendency to decrease the immobility duration in tail-suspension test was observed in BDNF-treated ASC mice. The effects on catalepsy and sexual motivation were specific since BDNF did not alter locomotor and exploratory activity or social interest in the ASC mice. Along with behavioral antidepressant-like effects on the ASC mice, BDNF increased hippocampal mRNA levels of Bdnf and Creb1 (cAMP response element-binding protein gene). BDNF also augmented mRNA levels of Arc gene encoding Arc (Activity-regulated cytoskeleton-associated) protein involved in BDNF-induced processes of neuronal and synaptic plasticity in hippocampus and prefrontal cortex. The data suggest that: [1] BDNF is effective in the treatment of some genetically defined behavioral disturbances; [2] BDNF influences sexually-motivated behavior; [3] Arc mRNA levels may serve as a molecular marker of BDNF physiological activity associated with its long-lasting behavioral effects; [4] ASC mouse strain can be used as a suitable model to study mechanisms of BDNF effects on hereditary-dependent behavioral disorders.