E. M. Kondaurova

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.

On the role of brain 5-HT7 receptor in the mechanism of hypothermia: Comparison with hypothermia mediated via 5-HT1A and 5-HT3 receptor

Intracerebroventricular administration of selective agonist of serotonin 5-HT(7) receptor LP44 (4-[2-(methylthio)phenyl]-N-(1,2,3,4-tetrahydro-1-naphthalenyl)-1-pyperasinehexanamide hydrochloride; 10.3, 20.5 or 41.0 nmol) produced considerable hypothermic response in CBA/Lac mice. LP44-induced (20.5 nmol) hypothermia was significantly attenuated by the selective 5-HT(7) receptor antagonist SB 269970 (16.1 fmol, i.c.v.) pretreatment. At the same time, intraperitoneal administration of LP44 in a wide range of doses 1.0, 2.0 or 10.0 mg/kg (2.0, 4.0, 20.0 μmol/kg) did not cause considerable hypothermic response. These findings indicate the implication of central, rather than peripheral 5-HT(7) receptors in the regulation of hypothermia. The comparison of LP44-induced (20.5 nmol) hypothermic reaction in eight inbred mouse strains (DBA/2J, CBA/Lac, C57BL/6, BALB/c, ICR, AKR/J, C3H and Asn) was performed and a significant effect of genotype was found. In the same eight mouse strains, functional activity of 5-HT(1A) and 5-HT(3) receptors was studied. The comparison of hypothermic responses produced by 5-HT(7) receptor agonist LP44 (20.5 nmol, i.c.v.) and 5-HT(1A) receptor agonist 8-OH-DPAT 1.0 mg/kg, i.p. (3.0 μmol/kg), 5-HT(3) receptor agonist m-CPBG (40.0 nmol, i.c.v.) did not reveal considerable interstrain correlations between 5-HT(7) and 5-HT(1A) or 5-HT(3) receptor-induced hypothermia. The selective 5-HT(7) receptor antagonist SB 269970 (16.1 fmol, i.c.v.) failed to attenuate the hypothermic effect of 8-OH-DPAT 1.0 mg/kg, i.p. (3.0 μmol/kg) and m-CPBG (40.0 nmol, i.c.v.) indicating that the brain 5-HT(7) receptor is not involved in the hypothermic effects of 8-OH-DPAT or m-CPBG. The obtained results suggest that the central 5-HT(7) receptor plays an essential role in the mediation of thermoregulation independent of 5-HT(1A) and 5-HT(3) receptors.

Effect of actual long-term spaceflight on BDNF, TrkB, p75, BAX and BCL-XL genes expression in mouse brain regions

Mice of C57BL/6J strain were exposed to 1-month spaceflight on Russian biosatellite Bion-M1 to determine the effect of long-term actual spaceflight on the expression of genes involved in the processes of neurogenesis and apoptosis. Specifically, we focused on the genes encoding proapoptotic factor BAX, antiapoptotic factor BCL-XL, brain-derived neurotrophic factor (BDNF) and BDNF receptors TrkB and p75. Spaceflight reduced the expression of the antiapoptotic BCL-XL gene in the striatum and hypothalamus, but increased it in the hippocampus. To estimate environmental stress contribution into spaceflight effects we analyzed spaceflight-responsive genes in mice housed for 1 month on Earth in the same shuttle cabins that were used for spaceflight, and in mice of the laboratory control group. It was shown that 1-month shuttle cabin housing decreased BCL-XL gene expression in the striatum but failed to alter BCL-XL mRNA levels in the hippocampus or hypothalamus. Spaceflight failed to alter the expression of the proapoptotic BAX gene in all investigated brain structures, although the insignificant increase of the BAX mRNA level in the hippocampus of spaceflight mice was found. At the same time, shuttle cabin housing produced insignificant decrease in BAX gene expression in the hippocampus. In contrast to the BCL-XL gene, genes encoding BAX, BDNF as well as TrkB and p75 receptors did not respond to 30-day spaceflight. Thus, long-term spaceflight (1) did not affect the expression of genes encoding BDNF as well as TrkB and p75 receptors, (2) produced dysregulation in genetic control of the neuronal apoptosis, (3) implicated BCL-XL as the risk factor for spaceflight-induced behavioral abnormalities.

Central 5-HT3 receptor-induced hypothermia in mice: Interstrain differences and comparison with hypothermia mediated via 5-HT1A receptor

The selective agonist of serotonin 5-HT(3) receptor 1-(3-chlorophenyl)biguanide hydrochloride (m-CPBG) administered intracerebroventricularly (40, 80 or 160 nmol) produced long-lasting dose-dependent hypothermic response in AKR/2J mice. m-CPBG (160 nmol i.c.v.) induced profound hypothermia (delta t=-4 degrees C) that lasted up to 7 h. m-CPBG (40 nmol i.c.v.)-induced hypothermia was attenuated by 5-HT(3) receptor antagonist ondansetron pretreatment. At the same time, intraperitoneal administration of m-CPBG in a wide range of doses (0.5, 1.0, 5.0 or 10.0 mg/kg) did not affect the body temperature. These findings indicate: (1) the implication of central, rather than peripheral 5-HT(3) receptor in the thermoregulation; (2) the inability of m-CPBG to cross blood-brain barrier in mice. The comparison of brain 5-HT(3)-induced hypothermic reaction in six inbred mouse strains (DBA/2J, CBA/Lac, C57BL/6, BALB/c, ICR, AKR/J) was performed and two highly sensitive to m-CPBG strains (CBA/Lac and C57BL/6) were found. In the same six mouse strains the functional activity of 5-HT(1A) receptor was studied. The comparison of hypothermic reactions produced by 5-HT(1A) receptor agonist 8-OH-DPAT (1.0 mg/kg i.p.) and m-CPBG revealed significant correlation between 5-HT(3) and 5-HT(1A)-induced hypothermia in five out of six investigated mouse strains. 5-HT(1A) receptor antagonist p-MPPI pretreatment (1 mg/kg i.p.) diminished hypothermia produced by centrally administered m-CPBG (40 nmol i.c.v.). The data suggest the cross-talk between 5-HT(1A) and 5-HT(3) receptors in the mechanism of 5-HT-related hypothermia.

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 chronic activation of 5-HT3 receptors on 5-HT3, 5-HT1A and 5-HT2A receptors functional activity and expression of key genes of the brain serotonin system

Among serotonin (5-HT) receptors, the 5-HT(3) receptor is the only ligand-gated ion-channel. Little is known about the interaction between the 5-HT(3) receptor and other 5-HT receptors and influence of 5-HT(3) chronic activation on other 5-HT receptors and the expression of key genes of 5-HT system. Chronic activation of 5-HT(3) receptor with intracerebroventricularly administrated selective agonist 1-(3-chlorophenyl)biguanide hydrochloride (m-CPBG) (14 days, 40 nmol, i.c.v.) produced significant desensitization of 5-HT(3) and 5-HT(1A) receptors. The hypothermic responses produced by acute administration of selective agonist of 5-HT(3) receptor (m-CPBG, 40 nmol, i.c.v.) or selective agonist of 5-HT(1A) receptor (8-hydroxy-2-(di-n-propylamino)tetralin) (8-OH-DPAT, 1mg/kg, i.p.) was significantly lower in m-CPBG treated mice compared with the mice of control groups. Chronic m-CPBG administration failed to induce any significant change in the 5-HT(2A) receptor functional activity and in the expression of the gene encoding 5-HT(2A) receptor. Chronic activation of 5-HT(3) receptor produced no considerable effect on the expression on 5-HT(3), 5-HT(1A), and 5-HT transporter (5-HTT) and tryptophan hydroxylase-2 (TPH-2) genes - the key genes of brain 5-HT system, in the midbrain, frontal cortex and hippocampus. In conclusion, chronic activation of ionotropic 5-HT(3) receptor produced significant desensitization of 5-HT(3) and postsynaptic 5-HT(1A) receptors but caused no considerable changes in the expression of key genes of the brain 5-HT system.

Brain-derived neurotrophic factor (BDNF) and its precursor (proBDNF) in genetically defined fear-induced aggression.

The brain-derived neurotrophic factor (BDNF), its precursor (proBDNF) and BDNF mRNA levels were studied in the brain of wild rats selectively bred for more than 70 generations for either high level or for the lack of affective aggressiveness towards man. Significant increase of BDNF mRNA level in the frontal cortex and increase of BDNF level in the hippocampus of aggressive rats was revealed. In the midbrain and hippocampus of aggressive rats proBDNF level was increased, whereas BDNF/proBDNF ratio was reduced suggesting the prevalence and increased influence of proBDNF in highly aggressive rats. In the frontal cortex, proBDNF level in aggressive rats was decreased. Thus, considerable structure-specific differences in BDNF and proBDNF levels as well as in BDNF gene expression between highly aggressive and nonaggressive rats were shown. The data suggested the implication of BDNF and its precursor proBDNF in the mechanism of aggressiveness and in the creation of either aggressive or nonaggressive phenotype.