[3H]SCH 23390 binding in various brain regions of C57BL/6J mice with repeated experience of victory or social defeat in agonistic interactions.

The binding of [3H]SCH 23390 has been studied in various brain regions of male mice with the experience of repeated victory (winners) or defeat (losers) gained over 10 (T10) and 20 (T20) days of daily agonistic confrontations. In the frontal cortex, B(max) of [3H]SCH 23390 binding sites was found to be increased in T10 losers and decreased in T20 losers when compared to the control mice. In the striatum, T10 and T20 winners had reduced values of [3H]SCH 23390 binding sites than the ones in the control mice. The K(d) was increased in the frontal cortex of T10 losers and T10 winners as well as in the amygdala of T20 losers. Reduced K(d) values were found in the striatum of all experimental groups as well as in the amygdala of T20 winners. Thus, both specific changes relating to social behavior patterns and non-specific ones in [3H]SCH 23390 binding were found in the brain regions of mice after 10 and 20 days of intermale confrontations.

Sex and gonadal steroid modulation of pheromone receptor gene expression in the mouse vomeronasal organ.

Non-volatile chemosignals in rodents are detected by unique receptors in the vomeronasal organ of the accessory olfactory system. Although the vomeronasal organ has been implicated in the regulation of sexually dimorphic behavioral and neuroendocrine functions, the underlying cellular mechanisms are undetermined. In previous studies we showed that exposure to soiled male bedding augmented immediate early gene immunoreactivity in neurons of the basal zone of the vomeronasal organ, an effect that depended on gender and sex steroid expression. To determine whether this effect could be due to differences in vomeronasal organ receptor expression, we examined two representatives (VR1 and VR4) from different subfamilies of the V2R family of receptors that are expressed in the basal zone of the vomeronasal organ. Adult Swiss-Webster male and female mice were gonadectomized and implanted with capsules containing 17beta-estradiol, testosterone or neither steroid (control). Two weeks later vomeronasal organs were processed for in situ hybridization using probes from the N-terminal extracellular domains of VR1 and VR4. Expression of both VR1 and VR4 was significantly higher in males than in females. Estradiol, but not testosterone-treated, males had significantly lower levels of VR1 expression in the caudal vomeronasal organ compared with untreated gonadectomized males. In contrast, testosterone enhanced VR4 expression in males relative to similarly treated females. Despite these effects, we found no evidence that vomeronasal organ neurons express either androgen or estrogen receptors. These data show that expression of vomeronasal organ receptors in mice is sexually dimorphic and regulated by sex steroids. Thus, gonadal hormones may affect the response of vomeronasal organ neurons to chemosignals by altering levels of the receptors to which they bind.

Increase in expression of brain serotonin transporter and monoamine oxidase a genes induced by repeated experience of social defeats in male mice.

Serotonin transporter and monoamine oxidase (MAO) A are involved in the inactivation of serotonin. The former is responsible for serotonin re-uptake from the synapse, whereas the latter catalyzes serotonin deamination in presynaptic terminals. Expression of serotonin transporter and MAO A genes was investigated in raphe nuclei of midbrain of CBA/Lac male mice with repeated experience of social victories or defeats in 10 daily aggressive confrontations. The amount of cDNA of these genes was evaluated using multiplex RT-PCR. Two independent experiments revealed that the defeated mice were characterized by significantly higher levels of serotonin transporter and MAO A mRNAs than the control and aggressive animals. Increased expression of MAO A and serotonin transporter genes is suggested to reflect the accelerated serotonin degradation in response to activation of the serotonergic system functioning induced by social stress. Significant positive correlation between MAO A and serotonin transporter mRNA levels suggests common pathways of regulation of transcriptional activity of these genes.

Increase of tyrosine hydroxylase and dopamine transporter mRNA levels in ventral tegmental area of male mice under influence of repeated aggression experience.

Tyrosine hydroxylase (TH) and dopamine transporter (DAT) mRNA levels in the ventral tegmental area (VTA) of midbrain were measured by multiplex RT-PCR in male mice with repeated experience of social victories (winners) and social defeats (losers) in 10 daily agonistic confrontations. Two independent experiments revealed enhanced TH and DAT mRNA levels in VTA of the winners in comparison with the losers and controls (animals after 5 days of individual housing). A positive correlation between DAT and TH mRNA levels was shown.

Fighting among C57BL/6J mice and its implications for [3H]8-hydroxy-N, N-dipropyl-2-aminotetralin binding in various brain regions.

The binding of [3H]8-hydroxy-N, N-dipropyl-2-aminotetralin ([3H] 8-OH-DPAT) has been studied in various brain regions of male mice with the experience of repeated victory (winners) or defeat (losers) gained over 10 (T10) and 20 (T20) days of daily agonistic confrontations. The Bmax of [3H]8-OH-DPAT binding sites was found to be decreased in the hippocampus of the T20 winners when compared to the T10 winners or the control mice, and increased in the amygdala of the T20 losers. The Kd was increased in the amygdala of the T20 losers when compared to the animals of any other experimental group. No change in [3H]8-OH-DPAT binding was observed in the midbrain or the hypothalamus of the winners or losers. It was concluded that the 20-day agonistic confrontations, arranged in order to categorize the mice as winners or losers, had opposing effects on [3H]8-OH-DPAT binding.

Features of the genetically defined anxiety in mice.

The behaviors of male mice of the C57BL/6J (C57), CBA/Lac (CBA) and BALB/c (BALB) strains have been studied in the plus-maze and open field tests for estimation of state anxiety in the stressful novel conditions, and in the cubic box test (exploration of novel cubic box) and the partition test (behavioral reactivity to the unfamiliar partner in the neighboring compartment) for estimation of trait anxiety in the unstressful familiar conditions of the home cage. Plus-maze data suggest that C57 mice are the more anxious than CBA and BALB ones. However, it was revealed the opposite rank order in the open field. The study on the effect of pre-testing in the one of test on the behavior in the other test revealed active behavioral strategy in C57 mice in any situations. The plus-maze behavior of CBA mice was affected to a much lesser extent than in C57 ones after pre-testing in the open field, but expressed changes were observed in open field behavior of CBA mice after pre-testing in the plus-maze. BALB mice displayed low-reactive behavior after any pre-testing exposure under the state anxiety-provoking conditions. Familiar environment revealed a higher level of trait anxiety in C57 than males of other two strains: CBA and BALB mice willingly explore unfamiliar partner and cubic box while C57 mice avoid its. Mainly genetically inherent state anxiety in CBA mice and trait anxiety in C57 mice has been suggested. Lowest state and trait indices of anxiety were revealed in BALB mice in these conditions.