Mice Reared with Rats: Modification of Behavior by Early Experience with Another Species

Abstract

Mice in group 1 (controls) spent all their lives with other mice. Mice in group 2 had experience only with male and female rats after weaning; group 3 mice had no experience with peers-each litter was reduced to one pup, which was reared in isolation after weaning; group 4 mice were fostered to a lactating rat mother at approximately 3 days of age and thereafter lived only with rats. In adulthood group 4 mice were the least active and group 3 the most; mice in groups 2 and 4 preferred to spend time in a chamber adjacent to a rat, those from groups 1 and 3 in a chamber containing another mouse; when mice were paired off within experimental groups and given the opportunity to fight each other, the percentage of pairs in which 4 were, respectively, 44,27,100, and 0.

Developmental Perspectives on Oxytocin and Vasopressin

“…The 'dark matter of social neuroscience' (Insel, 2010) is the gray area between perception and action, and is represented in a question like 'how does the adult brain identify a stimulus as 'social' so that it may act upon it?' This is both a mechanistic and a developmental question (Denenberg et al, 1964;Rosenblatt, 1983): early unconditioned stimuli in the environment such as maternal odor become paired with multisensory stimuli, which then acquire reinforcing properties. To many, it may come as a shock to see an effect of whisker trimming or dark rearing on a 'social neuropeptide' system like oxytocin-why does a non-social intervention like whisker trimming or total darkness reduce oxytocin content?…”

“…Their role in neonatal behavior is less well established, but deserves careful consideration, as this may significantly contribute to species-typical trajectories of experiencedependent development. Social expertise in adulthood is initiated by experience during development (eg, Denenberg et al, 1964), so alterations in infant activity that bring the infant in contact with social stimuli will positively contribute to the development of social expertise, while behavior that removes them from social contexts may negatively impact the development of species-typical social behavior.…”

“…Early orienting to specific odor cues is a significant contributor to mammalian species-typical social behavior developmental trajectories (Denenberg et al, 1964;Brunjes and Alberts, 1979;Rosenblatt, 1983;Balogh and Porter, 1986). Not unlike visual or auditory imprinting in many birds (Hess, 1959), olfactory imprinting in rodents helps to orient to the initial food source (the mother) and allows the infant to begin to build a neural representation of the social world through classical conditioning of innately social odor sources (eg, the mom, the littermates, species-typical food odors, and species-typical nest materials) with other stimuli (Rosenblatt, 1983;Hammock and Levitt, 2006;.…”

“…There is now an abundance of evidence that both oxytocin and vasopressin contribute to adult species-typical social behavior, including effects on human social behavior. As such examples of species-typical social behavior are influenced by both genetics (Lim et al, 2004;Hammock and Young, 2005) and early life experience (Denenberg et al, 1964;Pedersen and Boccia, 2002), a full understanding of the mechanisms of social behavior must include uncovering the genetic and neural circuit mechanisms of experience-dependent development.…”

“…Given the prevalence of developmental disorders and the contribution of early life experience to lasting outcomes, it is important to uncover the underlying mechanisms of experience-dependent development. What are the effector molecules of the early life social environment that lead to species-typical developmental trajectories for social behavior, such as preference for social contact with a conspecific, which requires developmental entrainment (Denenberg et al, 1964)? As a result of their prominent roles in adult social behavior, brain oxytocin and vasopressin systems appear as low hanging fruit in the garden of potential effector molecules underlying the developmental mechanisms of social behavior.…”