Serotonergic enhancement of synaptic transmission in rat medial vestibular nucleus

Abstract

To address the role of serotonergic projections to the medial vestibular nucleus (MV), whole-cell patch-clamp method was used to investigate serotonergic modulation of spontaneous synaptic transmission within the MV of young rats. Perfusion of serotonin (5-hydroxytryptamine, 5-HT) to brainstem slices greatly facilitated spontaneous inhibitory postsynaptic currents (sIPSCs) in a subgroup of MV neurons. That this enhancement effect of 5-HT on sIPSCs was abolished with tetrodotoxin indicated that 5-HT acted on its receptor that expressed in the presynaptic neurons. Using GABAA or glycine receptor antagonist, we further identified that both receptors took part in the enhancement effect of 5-HT on sIPSCs. This facilitatory effect could be mimicked with the administration of 5-HT2 receptor agonist but was blocked with 5-HT2A receptor antagonist. Similarly, 5-HT significantly increased both the amplitude and frequency of spontaneous postsynaptic currents (sEPSCs) in the MV circuitry. This 5-HT-induced enhancement of sEPSCs also depended on action potential. Such an enhancement of sEPSCs was abolished in the presence of CNQX. Further, 5-HT2 receptor agonist could mimic the 5-HT-induced facilitatory effect whereas 5-HT2A receptor antagonist blocked the effect. Our results therefore indicate that within the MV, 5-HT2A receptors expressed on presynaptic neurons function to facilitate both inhibitory and excitatory synaptic transmission.