Effect of Differential Space Use on Medial and Dorsal Cortical Neurogenesis in Side-Blotched Lizard, Uta stansburiana

Abstract

In the hippocampus, production of new and functional neurons is important for spatial memory function. Animals held in confined spaces or in captivity have been shown to decrease the production of new neurons, while those living in enriched environments have been shown to increase hippocampal neurogenesis, most likely due to an increased demand on memory function and spatial abilities. Here, I tested a hypothesis that the amount of space provided for exploration affects neurogenesis, and tested it by investigating neurogenesis in the medial and dorsal cortices of the brain in side-blotched lizards (Uta stansburiana), exposed to different spatial environments. Side-blotched lizards come in three different morphs—orange, blue, and yellow. Orange and blue sideblotched lizards hold territories and so are known as territorial; whereas the yellow morphs are non-territorial, since they do not defend territories. Territorial animals likely rely on spatial information to maintain and defend their territories, and I predicted that territorial lizards maintained in larger enclosures would have more new neurons than non-territorial lizards or individuals in smaller enclosures. Doublecortin was used to identify new neurons because it is only expressed in new, immature neurons. I found that territorial side-blotched lizards maintained in large enclosures had more newly produced cortical neurons than the non-territorial lizards, or individuals maintained in small enclosures. These results confirmed the hypothesis that larger space available for use stimulates production of neurons in the area of the brain involved in spatial learning. Interestingly, this effect was only observed in territorial morphs, suggesting that nonterritorial morphs may not necessarily use spatial learning during space exploration.