The regulatory roles of perineuronal semaphorin 3A and chondroitin sulfates on the developing vestibular circuitry

Abstract

Perineuronal nets (PN) are crucial for restricting neuronal plasticity during development. Our study of the central vestibular nucleus (VN) found consolidation of PN around GABAergic interneurons as from postnatal day (P)9 of Sprague Dawley (SD) rats. This was accompanied by progressive localization of semaphorin 3A (Sema3A) to chondroitin sulphate moieties (CS) of PN. We hypothesized that PN-CS binding of Sema3A limits the action of Sema3A as a plasticity-inducing factor in the VN. We tested for structural plasticity in VN explant cultures (P3+up to 31DIV) following treatment with chondroitinase ABC (ChABC) and/or Sema3A. Parallel cultures were fixed for assessment of neurite arborization and growth. Compared with null treatment controls, increase in these parameters suggested involvement of CS and Sema3A in controlling structural plasticity of VN neurons. To study the impact of PN-CS/Sema3A at the circuit level, the rats were assessed for the emergence of negative geotaxis as a read-out for maturation of the circuit for graviception. We observed negative geotaxis as early as P9, in correlation with consolidation of PN around GABAergic neurons in the VN. ChABC/Sema3A-treated rats showed delayed display of negative geotaxis, similar to effects of bicuculline but contrasting those of muscimol. The delay also correlated with postponed formation of PN after ChABC treatment, revealing that disturbance of PN consolidation interfered with maturation of the vestibular circuitry for graviception. We further performed whole-cell patch-clamp recordings of miniature excitatory post-synaptic current (mEPSC) from VN interneurons of P7/P9 rats, control versusthose treated with ChABC and Sema3A. We found increase in frequency of mEPSCs, suggesting strengthening of presynaptic signals along extended lengths of dendrites of interneurons in the ChABC/Sema3A-treated VN circuit. Our results provide evidence for the role of PN-CS-Sema3A in controlling structural and circuit plasticity at the interneuron level with impacts on the developmental display of graviceptive behaviour. [Grant Support HKRGC17125115M & 777911M]