Developmental plasticity of GABAergic synapses in medial vestibular nucleus of rats

Abstract

Inhibitory synaptic transmission within the vestibular nucleus is known to play a key regulatory role in coordinating central vestibular functions. To investigate the maturational changes of GABAergic transmission in medial vestibular nucleus, whole-cell patch-clamp experiments were conducted in brainstem slices of postnatal Sprague Dawley rats. Spontaneous inhibitory postsynaptic currents (sIPSCs) in medial vestibular neurons were isolated in the presence of ionotropic glutamate receptor antagonists (D-AP5 and CNQX). That these currents were abolished by GABAA receptor antagonist bicuculline indicates that the sIPSCs were mediated by GABAA receptor. The sIPSCs exhibited a gradual increase in frequency during the first two postnatal weeks and reached a plateau thereafter. Their amplitudes however did not change with postnatal development. To further investigate whether GABA receptors contribute to synaptic plasticity in the developing vestibular nucleus, a protocol consisting of repetitive depolarizing pulses at 0.1 Hz was used. Such stimuli did not induce any change in the amplitude of sIPSCs. Between P3 and P7, a majority of these GABAA receptor-mediated sIPSCs exhibited long-lasting frequency decrease after repetitive stimulation. From P14 to P22, however, only a small proportion of these sIPSCs showed such a long-lasting frequency decrease while the remaining neurons showed no change in frequency after repetitive stimulation. Taken together, we have demonstrated that long-term changes in GABAergic synaptic efficacy could be elicited in medial vestibular neurons during a limited time window of postnatal development.