Characterization of serotonin-induced inhibition of excitatory synaptic transmission in the anterior cingulate cortex

Excitatory synaptic transmission in central synapses is modulated by serotonin (5-HT). The anterior cingulate cortex (ACC) is an important cortical region for pain perception and emotion. ACC neurons receive innervation of projecting serotonergic nerve terminals from raphe nuclei, but the possible effect of 5-HT on excitatory transmission in the ACC has not been investigated. In the present study, we investigated the role of 5-HT on glutamate neurotransmission in the ACC slices of adult mice. Bath application of 5-HT produced dose-dependent inhibition of evoked excitatory postsynaptic currents (eEPSCs). Paired pulse ratio (PPR) was significantly increased, indicating possible presynaptic effects of 5-HT. Consistently, bath application of 5-HT significantly decreased the frequency of spontaneous and miniature excitatory postsynaptic currents (sEPSCs and mEPSCs). By contrast, amplitudes of sEPSCs and mEPSCs were not significantly affected. After postsynaptic application of G protein inhibitor GDP-β-S, 5-HT produced inhibition of eEPSCs was significantly reduced. Finally, NAN-190, an antagonist of 5-HT(1A) receptor, significantly reduced postsynaptic inhibition of 5-HT and abolished presynaptic inhibition. Our results strongly suggest that presynaptic as well as postsynaptic 5-HT receptor including 5-HT1A subtype receptor may contribute to inhibitory modulation of glutamate release as well as postsynaptic responses in the ACC.