UC Berkeley

Abstract

A Novel Model for the Exploration of Social Status in the Male Laboratory Rat:

Isolation of Psychosocial Factors and Effects of Early Environment

by

Matthew Wade Reid

Doctor of Philosophy in Psychology

University of California, Berkeley

Darlene D Francis, Chair

In humans virtually any measure of socioeconomic status (SES), i.e. income, education level, has an inverse association with both physical and mental health outcomes. Common theories to account for this observation involve scarcity of resources in lower SES populations and/or the impact of more challenging social environments, especially in early life, possibly resulting from resource inequality. It is precisely these variables (environment and resources) that confound our current understanding of the neural underpinnings associated with social status. These variables are impossible to control in human beings and, therefore, make us poor subjects from which to begin the study of social disparity.

Animal models of social hierarchy exist, but are not concerned with status as it relates to humans, as such, much of the information we have regarding the neural correlates of social status is derived from nonhuman adult organisms put in transient social environments where rank is determined by the outcomes of aggressive confrontation. Such research is primarily concerned with the effect of rank on the organism, not the underlying factors that may contribute to differences in rank generally and because of this environmental differences prior to these group formations are largely ignored.

We, therefore, developed a novel animal model of social status in which environmental experience was kept equal before group formation, and resource availability equal after. This approach allowed us to identify behavioral characteristics, brain areas, and physiological processes associated exclusively with the psychosocial experience of rank. We accomplished this by forming, to the best of our ability, social groups comprised of rats with identical characteristics (age, weight, sex, early experience) and provided ad libitum access to resources throughout our experiments. Intermittent bouts of competition for resources were used to characterize social rank and we performed oxytocin and vasopressin receptor autoradiography on brain areas implicated in processing characteristics of social, emotional and stressful stimuli.

Our goal, in addition to controlling environmental experience and resource inequality, was to recreate the graded pattern of effects evident in human SES research to validate the animal model's use as an instrument with which we could explore status relationships and generalize the results to human populations.

Based on the success of this new model we decided to explore the impact that naturally occurring variations in rat maternal care would have on social rank formation. The first experiment in this dissertation was conducted to ensure that differences in maternal care would impact social behavior in the rat in a measurable manner. As this was the case, we conducted the final study included in this dissertation and determined that maternal care does predict eventual social rank, but only in a particular social context. Several findings from the initial study employing our novel animal model were replicated in this experiment, adding to its value as a useful tool with which to explore social status.