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).