Glutamatergic synapses in the consciousness network and ACC
Using different experimental approaches, excitatory transmission in the ACC has been well documented (Bliss et al. , 2016). Glutamate serves as a principal excitatory transmitter for fast transmission since inhibition of glutamate AMPA and kainate (KA) receptors will abolish all basic excitatory transmission. Excitatory synapses onto cortical pyramidal cells are likely to be heterogeneous. In some synapses, postsynaptic currents are purely mediated by AMPA receptors, while in other synapses, both AMPA and KA receptors contribute to postsynaptic responses. KA receptor-mediated currents are usually small, however, in the case of the repetitive firing of action potentials, KA currents may summate generate big responses in part due to their slow kinetics (Wuet al. , 2005). Recent studies reported that silent synapses or pure NMDA receptor synapses exist in the adult cortex, including ACC (Zhuo, 2023). These silent synapses may contribute to a postsynaptic form of long-term potentiation (LTP) (post-LTP) (Figure 2).
In addition to its postsynaptic expression, presynaptic KA and NMDA receptors have also been reported in cortical synapses (Wu et al. , 2005; Koga et al. , 2015; Chen et al. , 2021). Activation of these receptors may contribute to the regulation of excitatory and inhibitory transmission. Furthermore, activation of KA receptors in the ACC has been reported to contribute to a presynaptic form of LTP (pre-LTP) (Koga et al. , 2015).