Hippocampal area CA2—a region of the hippocampus that is involved in social memory and aggressive behaviors—has been characterized in vole and hamster brain. These findings are detailed in a preprint released to BioRxivs by the Dudek group. While mice and rats are among the most commonly used animal models in neuroscience, other species such as Prairie Voles and Syrian Hamsters may be more suitable for some studies because of the unique prosocial and aggressive behaviors they exhibit, respectively. While area CA2 has been well described in mouse and rat, it had not been previously characterized in hamsters or voles. Understanding what area CA2 looks like in these species can help to facilitate future studies of social and aggressive behaviors.
Using antibodies raised against common area CA2 markers, Preston Siegler—a third year graduate student in the Dudek lab—performed immunofluorescence staining on fixed sections of mouse, vole, and hamster brain. This staining revealed a population of cells that exhibited common markers of area CA2 (RGS14 and PCP4) in a similar anatomical location and with similar distribution patterns in dorsal and ventral hippocampus. All three species also displayed similar staining of the stress hormone receptors, glucocorticoid (GR) and mineralocorticoid (MR) receptors. MR, which is one of the first markers of area CA2 to appear and is essential for the expression of other area CA2 markers, colocalized with the PCP4 positive cellular population while GR, commonly associated with area CA1, did not.
The main difference found from this study was that staining for perineuronal nets (PNNs)—specialized extracellular matrices thought to be involved in synaptic plasticity—only concentrated around area CA2 pyramidal neurons in mouse hippocampus. In vole and hamster, these PNNs were primarily found throughout area CA3 with sparse overlap with RGS14 positive cells that likely represent the proximal portion of area CA2. While the functional consequences of this differential PNN expression are unknown, this finding highlights some of the likely molecular differences between these rodent species. Overall, the findings of this study argue that vole and hamster do have a hippocampal area CA2, or at least a structure that is molecularly and anatomically similar to that in mice and that a critical role of area CA2 in hamster and vole social behaviors is plausible and worthy of further investigation. The manuscript is currently under consideration at the Journal of Comparative Neurology.
Full Abstract found here.