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.

Adult female hamsters avoid interspecific mating after exposure to heterospecific males

When females mate with a heterospecific male, they do not usually produce viable offspring. Thus, there is a selective pressure for females to avoid interspecific mating. In many species, females innately avoid heterospecific males; females can also imprint on their parents to avoid later sexual interactions with heterospecific males. However, it was previously unknown whether adult females can learn to discriminate against heterospecific males. We tested the hypothesis that adult females previously unable to avoid interspecific mating learn to avoid such mating after being exposed to heterospecific males. Syrian hamster (Mesocricetus auratus) females not previously exposed to Turkish hamster (Mesocricetus brandti) males can discriminate between odors of conspecific and heterospecific males, but they mate with either type of male. However, when we exposed adult females to both a conspecific male and a heterospecific male through wire-mesh barriers for 8 days, and then paired them sequentially with the two males, females were more receptive to conspecific males and more aggressive to heterospecific males. When females were paired with the heterospecific male first and the conspecific male second, no female was receptive and all were aggressive to heterospecific males. When females were paired with the conspecific male first, only 43% of females were then aggressive toward the heterospecific male. That is, interactions with conspecific males may decrease a female's ability to properly avoid heterospecific males. Our study clearly shows for the first time that females can learn during adulthood to avoid interspecific mating just by being exposed to stimuli from heterospecific males.

Comparative investigation of the volatile urinary profiles in different Phodopus hamster species

Stir bar sorptive extraction method was used for investigation of the urinary volatile profiles in male and female Phodopus campbelli and Phodopus sungorus hamsters. Additionally, female Phodopus roborowsky urinary profiles were characterized. A quantitative analytical approach allowed comparisons of 17 selected compounds in urine. Results showed that campbelli and sungorus species show similar urinary volatile profiles for males and females. Differences appeared only in concentrations. Several unique compounds, such as pyrazine derivatives, were found to be gender-and age-specific. P. roborowsky females exhibited a completely different urinary volatile profile from campbelli and sungorus females, featuring a unique set of substituted quinoxalines.

Maternal behavior in F344/N and LEW/N rats. Effects on carrageenan-induced inflammatory reactivity and body weight

Inbred Fischer (F344/N) and Lewis (LEW/N) rats differ on a myriad of behavioral and physiological endpoints, such as inflammatory, startle and drug responsivity. These differences point to underlying genetic differences between the strains. However, genetic models of hypertension have shown the importance of the maternal environment in the development of high blood pressure, suggesting that maternal influences might also play a role in adult phenotypes of the LEW/N and F344/N strains. This was tested in the present series of experiments in which the effects of crossfostering on carrageenan-induced inflammation and on body weight were examined in the two strains. Following the demonstration that the two strains differed in maternal behavior (Experiment 1), which was independent of the pup being reared (Experiment 2), crossfostered and in-fostered pups from the LEW/N and F344/N strains were injected with carrageenan (at 60 days of age) and subsequently assessed for the accumulation of exudate in response to the injection. Body weights were also monitored from birth through 60 days of age. Although crossfostering affected body weight of the two strains, specifically, reducing weights in LEW/N pups reared by F344/N dams and increasing weights of F344/N pups reared by LEW/N dams, crossfostering did not affect inflammatory reactivity to carrageenan. Specifically, LEW/N pups had a greater level of exudate than F344/N pups, independent of the conditions under which they were reared, suggesting that differences in the inflammatory response between these two strains are under a high degree of genetic control. These results were discussed in terms of genetic factors mediating the early form of immune reactivity induced by carrageenan.