Effect of MAO A deficiency on different kinds of aggression and social investigation in mice

Monoamine oxidase A (MAO A) degrades serotonin, dopamine and noradrenaline, factors critically involved in the regulation of aggression. Different kinds of aggression were investigated in Tg8, a transgenic mouse strain lacking a functional MAO A gene. MAO A-deficient mice differ from wild-type C3H/HeJ (C3H) in terms of showing higher territorial, predatory and isolation-induced aggression. Tg8 demonstrated shorter latencies to cricket killing and to the first attack after 6 weeks isolation than C3H mice. In the resident-intruder paradigm, MAO A-lacking mice were more aggressive than C3H when tested as intruders. In contrast to C3H, attack in Tg8 mice did not depend on different aggressiveness of intruders of BALB/c, A/Sn and C3H strains. Tg8 mice displayed no increase in aggression but demonstrated reduced social investigation towards anesthetized, as well as towards juvenile BALB/c males. Thus, MAO A deficiency in Tg8 mice is accompanied by increased expression of different kinds of aggression, as well as by disruption of normal pattern of social interaction.     

Beliefs in Equality for Women and Men as Related to Economic Factors in Central and Eastern Europe and the United States

Do economic indicators predict the general level of support for gender equality? This question was investigated in a sample of countries in Central and Eastern Europe, a region that has been undergoing rapid economic changes since the early 1990s. In this overall sample of male and female college students from ten countries, including the United States as a comparison, the predicted association between stronger beliefs in gender role egalitarianism and positive economic factors was generally supported. Also, consistent with other research, women were more in support of gender equality than men were. There was no support for a predicted trend in less support for gender equality over the time period of the present study.     

Association between intermale aggression and genetically-defined tryptophan hydroxylase activity in the mouse brain

The relationship between the genetically defined intensity of intermale aggression and the activity of brain tryptophan hydroxylase (TPH) has been studied in inbred mice. No association between the enzyme activity and the percentage of aggressive mice (reflecting the predisposition to aggressive reaction) was revealed. However, a significant positive interstrain correlation between brain TPH activity and accumulated attacking time (reflecting fight intensity) was identified. No correlation was found between TPH activity and the accumulated attacking time in segregating F2 (BALB × C57BL) mice. In conclusion, TPH is an important, but not the only factor controlling the intensity of intermale aggression in mice. © 1996 Wiley-Liss, Inc.     

Role of 5HT1A receptors in a variety of kinds of aggressive behavior in wild rats and counterparts selected for low defensiveness towards man

The 5HT_1A receptor agonist ipsapirone (10 mg/kg) suppressed shock-induced aggression in wild and domesticated rats but did not affect predatory aggression in either group of animals. Ipsapirone decreased neophobia and inhibited defensive reactions by wild rats towards man in the glove test. [³H]8-OH-DPAT binding, which labels 5HT_1A receptors, was significantly increased in the hypothalamus of domesticated rats in comparison with wild counterparts, while 5HT_1A density was unchanged in the frontal cortex in domesticated animals. In essence, the aggressive reactions contributing to the defensive behavior complex in wild rats appear to be regulated through 5HT_1A receptors. © 1992 Wiley-Liss, Inc.     

Selection for reduced aggressiveness towards man and dopaminergic activity in Norway rats

The brain dopaminergic system is involved in the process of long-term selection for reduced aggressive reaction towards man in Norway rats. The dopamine levels in the striatum as well as the nucleus accumbens with the tuberculum olfactorium were significantly lower in domesticated rats than in their wild counterparts. A substantial decrease was found in homovanillic acid level in the n. accumbens and tuberculum olfactorium. Specific binding of [³H]spiperone which labels D-2 dopamine receptors was higher in the mesolimbic structure of tame rats, whereas binding of [³H]SCH 23390 (D-1 receptors) was unchanged in this area. No substantial differences were detected in D-1 and D-2 binding in striatum. Apomorphine (0.3 mg/kg) elicited less locomotion in tame animals, reflecting a decrease of sensitivity of postsynaptic dopamine receptors. Tame rats showed fewer aggressive contacts in a foot-shock test than wild rats and the D-2 receptor antagonist sulpiride (25 mg/kg) significantly decreased the foot-shock aggression only in wild rats. Therefore, domestication, which diminishes defensive behavior and emotional reactivity of animals, is associated with decreases of dopamine level in the striatum, changed metabolism of dopamine in mesolimbic system, and an alteration in density and senstivity of D-2 receptors.     

Serotonin metabolism and serotonergic receptors in Norway rats selected for low aggressiveness to man

Selection of Norway rats (24–27 generations) for low aggressiveness to man resulting in the loss of aggressive responding to handling markedly influences the brain serotonergic system. In “domesticated” Norway rats levels of serotonin in the midbrain and hypothalamus and 5-hydroxyindole acetic acid in the hypothalamus were higher than in non-selected aggressive rats. The activity of the key enzyme in serotonin biosynthesis, tryptophan hydroxylase, in midbrain of rats with genetically determined lack of aggressiveness to man was higher than in aggressive animals, although there was no difference in tryptophan hydroxylase activity in the hypothalamus. B_max and K_D of [³H]spiperone-specific binding in frontal cortex membranes were increased in tame rats. No significant differences in B_max and K_D were found between “domesticated” and aggressive rats in [³H]serotonin binding in the frontal cortex.