Figure 3. Excitatory and inhibitory synapses in the cortex
Cortical pyramidal neurons receive excitatory and inhibitory innervation from projection and local neurons. In most cases, long-distance projections are excitatory, and local innervation si inhibitory. Cortical neurons also form excitatory connections within the same regions. Glutamate is the principle excitatory transmitter for excitation, and GABA is the key inhibitory transmitter. At postsynaptic sites, both AMPA and KA receptors may contribute to excitatory transmission, although these excitatory synapses are not homogenous. Some synapses only express functional AMPA receptors, and some synapses contain both of them. At presynaptic sites, there are KA receptors as well. For inhibitory transmission, GABAA receptor mediate most of inhibitory transmission. GABAB subtype receptor may distribute presynaptically to modulate the transmission.