Effects of the heterosomes and maternal environments on aggressive behavior in Mus musculus

A genetic context for the study of audiogenic seizures

Here, the genetic context for the study of audiogenic seizures is four single-gene, spontaneous mutations that occurred in the Behavior Genetics Laboratory at the University of Chicago from 1959 to 1969. Three of these increased the incidence of audiogenic seizures, and one of these decreased the incidence of audiogenic seizures. The genetics of one of these mutants is described in detail, and the effect of diet on the same mutant is also described in detail. Research on genetic and environmental effects on the cortical EEG of audiogenic seizures is reviewed; this research included two of these mutants. The cortical EEG associated with audiogenic seizures in this study was consistent with audiogenic seizures being a type of brain stem epilepsy as had been proposed by others. Also, I proposed that brain stem pathophysiology is the same regardless of the genetic or environmental pathway to audiogenic seizure susceptibility. Research is also reviewed using these mutants to determine whether or not a strain association between glutamic acid decarboxylase (GAD) activity in whole brain and susceptibility to audiogenic seizures is pleiotropic and whether or not a strain association between nucleoside triphosphatase (NTPase) activity in the granule cell layer of the dentate fascia of the hippocampus and susceptibility to audiogenic seizures is a lineal or collateral pleiotropy. Lastly, pleiotropy as an explanation for strain comorbidities in aggressive behavior and audiogenic seizures is considered. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

Foster dams rear fighters: strain-specific effects of within-strain fostering on aggressive behavior in male mice

It is well known that genes and environment interact to produce behavioral phenotypes. One environmental factor with long-term effects on gene transcription and behavior is maternal care. A classic paradigm for examining maternal care and genetic interactions is to foster pups of one genetic strain to dams of a different strain ("between-strain fostering"). In addition, fostering to a dam of the same strain ("within-strain fostering") is used to reduce indirect effects, via behavioral changes in the dams, of gestation treatments on offspring. Using within-and between-strain fostering we examined the contributions of genetics/prenatal environment, maternal care, and the effects of fostering per se, on adult aggressive behavior in two inbred mouse strains, C57BL/6J (B6) and DBA/2J (DBA). We hypothesized that males reared by dams of the more aggressive DBA strain would attack intruders faster than those reared by B6 dams. Surprisingly, we found that both methods of fostering enhanced aggressive behavior, but only in B6 mice. Since all the B6 offspring are genetically identical, we asked if maternal behavior of B6 dams was affected by the relatedness of their pups. In fact, B6 dams caring for foster B6 pups displayed significantly reduced maternal behaviors. Finally, we measured vasopressin and corticotrophin releasing hormone mRNA in the amygdalae of adult B6 males reared by foster or biological dams. Both genes correlated with aggressive behavior in within-strain fostered B6 mice, but not in mice reared by their biological dams. In sum, we have demonstrated in inbred laboratory mice, that dams behave differently when rearing their own newborn pups versus pups from another dam of the same strain. These differences in maternal care affect aggression in the male offspring and transcription of Avp and Crh in the brain. It is likely that rearing by foster dams has additional effects and implications for other species.

Parent-of-origin and trans-generational germline influences on behavioral development: the interacting roles of mothers, fathers, and grandparents

Mothers and fathers do not contribute equally to the development of their offspring. In addition to the differential investment of mothers versus fathers in the rearing of offspring, there are also a number of germline factors that are transmitted unequally from one parent or the other that contribute significantly to offspring development. This article shall review four major sources of such parent-of-origin effects. Firstly, there is increasing evidence that genes inherited on the sex chromosomes including the nonpseudoautosomal part of the Y chromosome that is only inherited from fathers to sons, contribute to brain development and behavior independently of the organizing effects of sex hormones. Secondly, recent work has demonstrated that mitochondrial DNA that is primarily inherited only from mothers may play a much greater than anticipated role in neurobehavioral development. Thirdly, there exists a class of genes known as imprinted genes that are epigenetically silenced when passed on in a parent-of-origin specific manner and have been shown to regulate brain development and a variety of behaviors. Finally, there is converging evidence from several disciplines that environmental variations experienced by mothers and fathers may lead to plasticity in the development and behavior of offspring and that this phenotypic inheritance can be solely transmitted through the germline. Mechanistically, this may be achieved through altered programming within germ cells of the epigenetic status of particular genes such as retrotransposons and imprinted genes or potentially through altered expression of RNAs within gametes.

Integrative focus on dynamic motor patterns and age hierarchy in the expression of aggression

In this study, we analyzed the dynamic motor patterns of attack or defense and age hierarchy to investigate aggression in African mole-rats Cryptomys foxi and the house mouse Mus musculus. The objective is to verify if the social order of dominance is associated with age hierarchy within the social group. Using the resident-intruder experimental model, we created a series of dyadic encounters that comprised of a standard adult mouse or rat paired with groups of aggressive and hierarchically age-ranked small animals in a territorial aggression test. Our results indicate that though the adult animals displayed the highest level of aggression, indicating their dominant status, there was no age-related hierarchical formation in the expression of aggression. In the non-territorial aggression test in which rats or mice were grouped together, animals displayed low levels of aggression compared to the territorial test and no hierarchical age-related order. These results indicate that the magnitude of aggression expressed by animals in the social group, based on their motor patterns of attack and defense, seem to depend on individual competitive strategies in reaction to various environmental challenges and not necessarily on age hierarchy.

Y chromosome, urinary chemosignals, and an agonistic behavior (offense) of mice

In mice, offense is one type of agonistic behavior associated with attacks. Offense of male mice was measured in a panel of testers design. The mice were DBA1 (D1) and DBA1.C57BL10-Y (D1.B10-Y). These are congenic for the male-specific, nonrecombining part of the Y chromosome. For the behavioral experiments, urine from D1 or D1.B10-Y mice was daubed on gonadectomized opponents. The opponents were of two genotypes, D1 or D1.B10-Y. The experimental subjects were of the same two genotypes. There were main effects for strain of experimental subject and strain of urine donor as well as interactions for strain of experimental subject x strain of gonadectomized opponent, strain of gonadectomized opponent x strain of urine donor, and strain of experimental subject x strain of gonadectomized opponent x strain of urine donor. These findings are consistent with a model in which this part of the Y chromosome affects testosterone-dependent pheromones and non-testosterone-dependent odor types acting as motivating stimuli, the olfactory perception of motivating stimuli for offense, and the motivational mechanism for offense.

Genetic analysis of isolation-induced aggression. I. Comparison between closely related inbred mouse strains

Young adult males of the inbred mouse strains BALB/c, C57BL/6, CBA, C3H/He, and the outbred strain NMRI showed significant interstrain differences for isolation-induced aggression as measured in a standard-opponent test. Additionally, four related inbred strains of common origin (ABG, AB//Halle, ABB, AB//Jena) were studied. ABG and AB//Halle showed nearly no overlap for the trait isolation-induced aggression. Tests of histocompatibility and coat color, as well as mandible measurements, confirmed a close genetic relationship between ABG and AB//Halle. The large difference for isolation-induced aggression between these two closely related strains offers excellent opportunities to search for single gene correlates of aggression.