Mechanisms by which perineuronal nets promote hardwiring of vestibular circuits for sensori-motor behaviors

Abstract

Chondroitin sulphate (CS)-rich perineuronal nets (PN) have emerged as a powerful regulator of plasticity. We asked how PN governs early brain development. Consolidation of PN around GABAergic neurons in the VN coincides with emergence of vestibular-dependent negative geotaxis behavior at P9 in rats. Treatment of the VN at P6 with chondroitinase ABC (ChABC) to delay consolidation of PN resulted in shift of negative geotaxis to P13. To elucidate the effect of ChABC treatment at the cellular level, we performed whole-cell patch-clamp recordings on VN interneurons in brainstem slice preparations at P9 and P14 when PN-CS underwent consolidation. Pre-treatment of the VN with ChABC decreased inhibition but promoted excitatory neurotransmission in VN neurons. We found that ChABC treatment increased excitability of VN neurons due to increase in membrane potential. Apart from this direct effect, we further showed that the PN-CS associated plasticity-inducing factor semaphorin 3A (Sema3A) was liberated with treatment of ChABC. In vitro tests confirmed that Sema3A promoted neurite growth and branching of VN neurons. To reveal the behavioral consequence, we compared Sema3a treatment alone with combined ChABC and Sema3A delivery to the VN at P6. Sema3A delayed the emergence of another graviceptive reflex air-righting from P15 to P16, while combined treatment further delayed it to P18. Taken together, our results suggest that retention of Sema3A by PN-CS moieties limits dendritic/synaptic plasticity of VN interneurons, thereby contributing to developmental hardwiring of the central circuitry for vestibular behavior.