Interaction of genotype and fostering in the development of behavior of DBA and C57 mice

A Neuroscientist's Guide to the Vole

Prairie voles have emerged as an important rodent model for understanding the neuroscience of social behavior. Prairie voles are well known for their capacity for pair bonding and alloparental care. These behavioral phenomena overlap with human social behavior but are not commonly observed in traditional rodent models. In this article, we highlight the many benefits of using prairie voles in neuroscience research. We begin by describing the advantages of using diverse and non-traditional study models. We then focus on social behaviors, including pair bonding, alloparental care, and peer interactions, that have brought voles to the forefront of social neuroscience. We describe many additional features of prairie vole biology and behavior that provide researchers with opportunities to address an array of research questions. We also survey neuroethological methods that have been used with prairie voles, from classic to modern techniques. Finally, we conclude with a discussion of other vole species, particularly meadow voles, and their own unique advantages for neuroscience studies. This article provides a foundation for researchers who are new to working with voles, as well as for experienced neuroscientists who want to expand their research scope. © 2021 Wiley Periodicals LLC.

Cross-fostering: Elucidating the effects of gene×environment interactions on phenotypic development

Cross-fostering of litters from soon after birth until weaning is a valuable tool to study the ways in which gene×environment interactions program the development of neural, physiological and behavioral characteristics of mammalian species. In laboratory mice and rats, the primary focus of this review, cross-fostering of litters between mothers of different strains or treatment groups (intraspecific) or between mothers of different species (interspecific) has been conducted over the past 9 decades. Areas of particular interest have included maternal effects on emotionality, social preferences, responses to stressful stimulation, nutrition and growth, blood pressure regulation, and epigenetic effects on brain development and behavior. Results from these areas of research highlight the critical role of the postnatal maternal environment in programming the development of offspring phenotypic characteristics. In addition, experimental paradigms that have included cross-fostering have permitted investigators to tease apart prenatal versus postnatal effects of various treatments on offspring development and behavior.

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.

Emotional reactivity in mice may not be inherited but influenced by parents

Heredity is often assimilated to genetic transmission of traits. However, some traits may be socially inherited. This has been described for maternal behaviour as well as for emotional reactivity in rodents such as rats or mice. The aim of the present study was to investigate further this idea using two backcrosses between CB6 or B6C females and C57BL/6 males. Indeed, the experimental groups are genetically identical but may be exposed to very different mothering types. When adults, the offspring were subjected to rodent emotional reactivity tests such as elevated plus maze and free exploration paradigm. Results show that CB6xB6 males exhibit higher emotional reactivity than B6CxB6 and B6 males in all behavioural situations, but these effects are not seen in females. Contrarily to their offspring that show different reactivity even if sharing the same genetical background, CB6 and B6C females display quite identical emotional reactivity. A possible explanation is that emotional reactivity is induced by maternal behaviour rather than transmitted by the parents.

Emotional reactivity in mice, a case of nongenetic heredity?

Nongenetic heredity cases have been described in man, as well as in animals, and relationships between parents and offspring seem to play an important role in this transmission. In mice, mothering type could be nongenetically heritable by a latent learning close to mechanism. As mothering style clearly influences emotional reactivity, this reactivity could be nongenetically transmitted over generations. To clarify this question, the mother's influence on adult offspring reactivity must be established (whatever its basis, genetic, social or other). Thus, two reciprocal F1 hybrids (CB6 from a BALB/c mother and B6C from a C57BL/6 mother) have been compared using an ethological analysis in animal tests of emotional reactivity such as the free exploration paradigm and the light/dark box. First results show a sharp influence of the mother's strain and that suggests an effect of mothering style. The offspring from C57BL/6 mothers display less reactivity in the free exploration paradigm than the offspring from BALB/c mothers. In the light/dark box, no difference has been found between the two hybrids. Moreover, the mother's influence is greater in males than in females.

Thermal preference behavior in preweaning genetically obese (ob/ob) and lean (+/?, +/+) mice

Impaired nonshivering thermogenesis and lowered rectal temperatures (Tre) are hallmarks that appear early in the postnatal ontogeny of the genetically obese (ob/ob) mouse. Adult obese mice compensate behaviorally for these impairments and do not defend their low Tres. We predicted that, because young mice primarily rely on behavior to ensure thermal homeostasis during preweaning development, the appearance of the obese mouse's thermoregulatory impairment should promote their continued reliance on behavioral thermoregulation compared to lean pups. Accordingly, intact litters of pups from heterozygous lean (C57BL/6J, ob/+) and from homozygous lean (+/+) matings were tested at 6, 12, and 18 days postpartum on a thermal gradient (14-44 degrees C). Obese pups had lower pretest Tres than lean (+/?) littermates at 6 days and lower pretest Tres than both lean littermates and homozygous (+/+) lean control pups at 12 and 18 days. Exposure to the gradient ameliorated these differences (i.e., no posttest Tre differences among phenotypes). Correspondingly, obese pups preferred warmer gradient locations than +/+ pups but similar locations to their phenotypically lean (+/?) littermates until 18 days, when both lean groups preferred similar thermal locations compared to warmer-seeking obese pups. These data support our hypothesis and emphasize the age-dependent impact of the ob gene on altering mouse pups' thermal preferences.

Early development in mice. IV: Quantity and gross composition of milk in five inbred strains

An analysis of the gross composition of milk in five inbred strains of mice (NZB, CBA/H, BALB/c, C57BL/6, XLII) was conducted for two different days during the lactating period (6th and 9th day after parturition). The quantity of milk and the concentration of proteins, lactose and lipids were measured. Results show a significant effect for day on the quantity of milk, but not for strain. Day effect was also observed for proteins and lactose; however modifications in the concentration of lactose and lipids from the 6th to the 9th day were not identical across strains. Also, a strain effect was present for proteins, lipids and lactose.

Persistent inverse maternal effect on corticosterone production in vitro

Adrenal cells from C57BL/Tb mice produced more steroid than those from DBA/2J mice. Reciprocal differences between both backcross and F1 hybrids showed a persistent maternal effect. Mothers with high output produce offspring with reduced hormone production when adult. Corticosterone output thus depends on maternal phenotype as well as on the genotype of the isolated cells.

Early development in mice: I. Genotype and post-natal maternal effects

The co-actions of genetic effects and the post-natal maternal rearing environment on the development of weight, 9 reflex responses, and survival have been tested by the cross-fostering method in two inbred mice strains--CBA/H and NZB. Pups of the two strains were not treated differentially by the mothers and experimental handling did not systematically affect pup development. Comparisons of unfostered, infostered, and cross-fostered pups show (1) in 16 cases out of 34, reflex development was affected by the pup strain, and in 10 cases out of 34 by the foster mother strain; (2) survival is only affected by the pup strain; (3) weight development is affected by strain of both the pup and the mother as well as their interactions. The adopted pups' scores were situated outside the range of the two non-adopted groups for certain reflexes as well as for weight. Two non-exclusive hypotheses are proposed: the mother strain can affect pup development (1) either through differences in stimulation provided by the mothers (2) or through differences in milk composition.