Perineuronal Chondroitin Sulfates Disruption Interferes Excitation/Inhibition Balance in Developing Vestibular Circuitry

Abstract

Perineuronal nets (PN) are implicated in restricting neural plasticity with the maturation of neural circuits. Our study of the central vestibular nucleus (VN) found consolidation of PN around GABAergic interneurons, especially the parvalbumin-expressing ones, as from postnatal day (P)9 of Sprague Dawley (SD) rats. Cleavage of chondroitin sulfates (CS) chains by microinjection of chondroitinase ABC (ChABC) resulted in delay of PN formation from P9 to P13 and delay the vestibular-dependent behavior acquisition, air righting, from P15 to P17. We hypothesized the delay of PN formation would affect the excitation/inhibition (E/I) balance in developing vestibular circuitry and subsequent vestibular-dependent behavioral acquisition. To find if cleavage of PN-CS by ChABC injection impacts on inhibition and excitation circuitry in VN during development, whole-cell patch-clamp recordings of spontaneous inhibitory post-synaptic GABA receptor-mediated current (sIPSC) and spontaneous excitatory post-synaptic AMAP receptor-mediated current (sEPSC) from VN interneurons were performed in brainstem slice preparations of P9 and P14 rats following test treatment with ChABC in the VN of P6 rats. Significant reduction of sIPSC frequency and enhancement of sEPSC amplitude indicated disruption of PN-CS interfere the balance of excitation and inhibition in the circuitry during development. The disruption of E/I balance was also confirmed by E/I ratio measurement after acute ChABC treatment by simultaneous recording of sIPSC and sEPSC from VN neurons. The results suggest plasticity triggered by CS disruption at excitatory and inhibitory synapses onto otherwise PN-enwrapped neurons in the VN circuit. To analyze pre- and post-synaptic changes of inhibitory input after ChABC treatment, paired-pulsed stimulation was performed. Significant decline of amplitude of eIPSC, but not PPR, implied postsynaptic changes of GABAergic synapse. After ChABC microinjection into VN, significant decrease of miniature IPSC (mIPSC) during development confirmed that the number of GABAA receptors was reduced on postsynaptic membrane. PN has high binding affinity with plasticity inducing factor, Semaphorin 3A (Sema3A), which binds to its receptor complex and regulates AMPA receptors (AMPAR) localization. We hypothesized that disruption of PN-CS released Sema3A for interfering excitatory input during development. The increased amplitude of miniature excitatory postsynaptic AMPA-mediated current (mEPSC) suggested the elevation of AMPAR on postsynaptic membrane after ChABC microinjection. Our results reveal that PN consolidation around VN interneurons is a key step in controlling structural and circuit plasticity and E/I balance for developmental display of graviceptive behaviour. Acknowledgement: The project is supported by general research fund (RGC-GRF 17125115 )