Behavioral characteristics of mice with genetic knockout of monoamine oxidase type A.

Transgenic mice of line Tg8 were used to study the effects of deletion of the monoamine oxidase type A gene and the absence of the corresponding enzyme on behavior. These experiments showed that Tg8 mice with genetic knockout of monoamine oxidase type A differed from mice of the parental line C3H/HeJ by lower levels of the startle reflex in response to an acoustic signal, while there was no difference in the prestimulus inhibition of the startle response. Tg8 mice showed decreased investigative activity and decreases in the number of sector crossings in the light-dark anxiety test. There were significant increases in aggression as a motivation in male Tg8 mice, which was manifest as an increase in the number of mice demonstrating aggression and a decrease in the latent period of attack. The intensity of aggression changed to a lesser extent - the number of fights even decreased, though longer periods of keeping mice together resulted in increased numbers of deaths among intruder mice. At the same time, there were no significant differences between mice with genetic knockout of monoamine oxidase type A and control mice in terms of the expression of sexual activation: the behavioral responses of Tg8 males to presentation of females was marked and was no different from that of male C3H/HeJ mice. Knockout of the gene had no effect on movement activity on behavior in an elevated cross-shaped maze or in the test for predisposition to catalepsy.