In a recent study published in Cerebral Cortex entitled “Presynaptic GABAa Receptors Modulate Thalamocortical Inputs in Layer 4 of Rat V1”, Dr. Lang Wang and her colleagues reported an exciting existence of presynaptic GABAa receptors selectively expressed on thalamocortical axon terminals by combining electrophysiology, optogenetic and EM approaches, which provides a novel mechanistic insight into the effects of changes in cortical inhibition and the ability to modulate inputs onto cortical circuits locally via presynaptic GABAa receptors.
Neocortical GABAergic neurons are diverse and connect broadly to excitatory neurons, providing cortical circuits with sophisticated computational control of neuronal activity. While there is general agreement regarding the involvement of fast GABAa receptor-mediated inhibition in the control of circuit excitability, several unresolved issues remain concerning how this regulation is achieved. The current thinking is that GABAa receptors are located mainly at postsynaptic and extrasynaptic sites in neocortex, thus manipulation of fast inhibition would only affect intracortical circuits, while leaving incoming afferent inputs unaffected. Here we report that GABAa receptors containing specific subunits are selectively present on presynaptic terminals of thalamocortical (TC) inputs in L4, the main input layer of primary visual cortex (V1), which can be activated in response to GABA release by local high frequency firing of inhibitory neurons, thus decreases neurotransmitter release and modulates short-term plasticity. These results suggest an important role for presynaptic GABAa receptors on TC synapses in regulating local circuit excitability, gating TC information to V1, and providing a novel mechanism for local corticothalamic feedback.
Below is the link to access the article: https://www.ncbi.nlm.nih.gov/pubmed/29373653