Perineuronal Nets in Syrian Hamsters: Anatomical Localization, Sex Differences, Diurnal Variation, and Response to Social Stress.

Purpose: Perineuronal nets (PNNs) are extracellular matrix proteoglycans surrounding neurons and glia. It has been suggested that PNNs are involved in the pathophysiology of multiple CNS illnesses, including stress‐related neuropsychiatric disorders like schizophrenia, major depressive disorder, and anxiety disorders. Method: Before examining the putative role of PNNs in stress‐related responses, we described for the first time the anatomical distribution in Syrian hamsters (Mesocricetus auratus), an excellent model organism for studying social stress and circadian rhythms. Results: We observed PNNs throughout the hamster cortex and hippocampus but found low to no expression in subcortical regions such as the hypothalamus, thalamus, and striatum, sites where they are observed in rats and mice. We further demonstrated that PNNs are dynamically regulated in a sex‐dependent manner in response to acute social stress, specifically in hippocampal area CA1. We did not observe a difference in PNNs between the beginning of the dark versus light phase of the light–dark cycle in hamsters, despite other laboratory rodents showing diurnal variation in PNNs. Finally, we also demonstrated that there are sex differences in PNN expression in the somatosensory cortex and the basolateral amygdala in hamsters, suggesting that sex as a biological variable should be considered in studies of PNN function. Conclusion: Together, the data from the current study suggest that a comparative approach will be necessary to fully elucidate the functional role of PNNs and, further, that Syrian hamsters are a valuable model in this endeavor. [ABSTRACT FROM AUTHOR]