Figure 2. Different forms of LTPs in cortical excitatory
synapses
Two major forms of LTPs have been reported in the ACC excitatory
synapses: presynaptic form of LTP (pre-LTP) and postsynaptic form of LTP
(post-LTP). In pre-LTP, the induction requires activation of glutamate
KA receptors at presynaptic side. Postsynaptic activation of NMDA
receptor is not required. The expression of pre-LTP is due to more
release of glutamate from presynaptic terminals. For post-LTP,
activation of NMDA receptors is required. The expression is mainly
mediated by the phosphorylation of AMPA receptors by cAMP PKA signalling
pathways. In addition, some synapses may be silent before the LTP
induction, the expression of functional AMPA receptors in these synapses
may also contribute to post-LTP. For long-lasting form of LTP, gene
regulation and protein synthesis are required.