The role of perineural networks in-memory storage
Perineuronal networks (PNNs) play a key role in the maturation and plasticity of neurons and synapses. PNNs affect the formation, retention, and extinction of memory in various animal models. According to a recently published study, the eyes and cavities in the PNN contain synapses and can therefore function as a memory repository that is even stable in conditions during which synapse retraction occurs, such as anoxia or hibernation. We studied this theory in mice put into a state resembling hibernation, in which there is a retraction of synapses and, at the same time, we monitored the spatial memory of these animals before and after hibernation. We used normal animals and animals that had an absence of nets in the hippocampus area; either due to cleavage by the enzyme chondroitinase ABC or genetically removed aggrecan, which is an important part of PNN. In our model, synapse retraction during hibernation caused memory deficits, but not to the level of naive animals. Both groups with enzymatically cleaved networks (hibernating and non-hibernating) had changes in the level of synaptic proteins located on parvalbumin neurons in the hippocampus during and after hibernation, which resulted in faster re-learning in the Morris water maze compared to mice in hibernation and the retraction of synapses preserved by PNN. Chondroitinase did not alter the memory deficit, while the long-term absence of PNN in the aggrecan knockout group led to partial memory retention, but there was no improvement in re-learning the task in the water maze.