Manipulating the Perineuronal Net in the Deep Cerebellar Nucleus

Abstract

Perineuronal nets (PNN) are a type of specialized extracellular matrix in the central nervous system. The PNN forms during postnatal development but the ontogeny of the PNN has yet to be elucidated. Studying the PNN in the rat brain may allow us to further understand the PNN’s role in development, learning, and memory. The PNN is fully developed in the deep cerebellar nuclei (DCN) of rats by post-natal day 18. By using enzymatic digestion of the PNN with chondroitinase ABC (ChABC), we studied how digestion of the PNN affects cerebellar-dependent eyeblink conditioning (EBC) and performed electrophysiological recordings from DCN neurons. In vivo degradation of the PNN resulted in differences in EBC amplitude and area. Female animals in the vehicle group demonstrated higher levels of conditioning as well as higher post-probe conditioned responses compared to males in that group, differences not present in the ChABC group. In vitro, DCN neurons with disrupted PNNs following exposure to ChABC had altered membrane properties, fewer rebound spikes, and decreased intrinsic excitability. Doxycycline, an antibiotic, can inhibit endogenous enzymes that digest the PNN. Rats given doxycycline had higher PNN staining in the DCN compared to vehicle. Animals receiving doxycycline prior to behavior have a smaller eyeblink area in comparison to the vehicle group. However, these rats also had more unconditioned responses, suggesting in addition to preventing the PNN from being remodeled, doxycycline may cause non-associative effects. This study further elucidates the role of the PNN in cerebellar learning.