The visible burrow system, comprising an open field, tunnels, and chambers, provides rats with a seminaturalistic environment. Rats housed in such a structure explore the field, sleep in the chambers, and compete for access to food and water via two narrow ramps. These behaviors and, in particular, the associated social interactions result in the establishment of a dominance hierarchy after only 3 days of habitation.
Kozorovitskiy and Gould document the extent of neurogenesis in the dentate gyrus of the hippocampal formation as a function of social position. They find that subordinate and dominant rats generate the same number of new neurons, but that more of these cells survive in the more aggressive individuals. The difference in number does not appear to be due directly to stress (which might be expected to dampen neurogenesis), because corticosterone levels did not differ; it is possible, however, that behavioral history may influence the glucocorticoid sensitivity of neuronal proliferation, as suggested by Mirescu et al. in a related study. — GJC
J. Neurosci. 24, 6755 (2004); Nature Neurosci. 7, 841 (2004).