ABSTRACT
The transmission processes mediated by Glu and GABA are very complex and highly regulated. A general and simple model for the Glu and GABA neurotransmission is shown in Figure 15.1. Glu and GABA are formed in their respective presynaptic nerve terminals and upon depolarization released into the synaptic cleft in high concentration to activate postsynaptic ionotropic receptors that directly modify the membrane potential of the receptive neuron, generating an excitatory or inhibitory postsynaptic potential. This basic system is further modulated through G-protein-coupled receptors (GPCRs) for a variety of neuroactive substances, including Glu and GABA themselves. Subsequently, Glu and GABA are removed from the synaptic cleft into surrounding neurons and glia cells via specialized transporters to restore the neurotransmitter balance. The reuptaken Glu is enzymatically metabolized to form glutamine (Gln) or α-ketoglutarate, whereas GABA is converted to succinic acid semialdehyde.
