Abstract
Perineuronal nets (PNNs) accumulate around neurons near the end of developmental critical periods. PNNs are structures of the extracellular matrix which surround synaptic contacts and contain chondroitin sulfate proteoglycans. Previous studies suggest that the chondroitin sulfate chains of PNNs inhibit synaptic plasticity and thereby help end critical periods. PNNs surround a high proportion of neurons in the cerebellar nuclei. These PNNs form during approximately the same time that movements achieve normal accuracy. It is possible that PNNs in the cerebellar nuclei inhibit plasticity to maintain the synaptic organization that produces those accurate movements. We tested whether or not PNNs in a saccade-related part of the cerebellar nuclei maintain accurate saccade size by digesting a part of them in an adult monkey performing a task that changes saccade size (long term saccade adaptation). We use the enzyme Chondroitinase ABC to digest the glycosaminoglycan side chains of proteoglycans present in the majority of PNNs. We show that this manipulation does not result in faster, larger, or more persistent adaptation. Our result indicates that intact perineuronal nets around saccade-related neurons in the cerebellar nuclei are not important for maintaining long-term saccade gain.
Highlights
Perineuronal nets (PNNs) are features of the CNS extracellular matrix that surround synaptic contacts on the soma and dendrites of neurons
ChABC degrades CSPGs of perineuronal nets in macaque cerebellar nuclei Table 1 shows the size of the injections into the four sites outside the CFN
We found that our ChABC injections completely digested CS chains of CSPGs in perineuronal nets 7 days after our injection series started
Summary
Perineuronal nets (PNNs) are features of the CNS extracellular matrix that surround synaptic contacts on the soma and dendrites of neurons (reviewed by [1,2,3]). PNNs are composed of several molecules, including hyaluronan, link proteins and chondroitin sulfate proteoglycans (CSPGs) (reviewed by [2,3,4]). CSPGs consist of a protein core and a variable number of chondroitin sulfate side chains (CS chains) Several recent studies reestablish critical period-like high levels of plasticity by enzymatically digesting CS chains in perineuronal nets of adult rats [9,13,14] and mice [15]
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