Gaba_A receptors control the excitability of neuronal populations

This chapter focuses on the role of GABA_A receptor function in the collective behavior of cortical neuronal populations, primarily in the hippocampal formation. Experimental accessibility, plasticity, and a prominent role in learning and memory account for numerous anatomical, biochemical, and physiological studies in this brain region. GABA-mediated inhibition occurs through two physiological mechanisms: An increase in membrane conductance and a hyperpolarization of the postsynaptic membrane. The combination of features of GABAergic inhibition, the distribution and widespread dendritic arborization of GABAergic interneurons, the ubiquitous subcellular distribution of GABA_A and GABA_B receptors, the concentration of GABA_A receptors at strategically pivotal sites close to the cell soma, the large chloride conductance increases produced by shunting inhibition, and the generation of spontaneous IPSPs indicate a very powerful inhibitory control of a given cell population in the mammalian cortex. Under physiological conditions, the state of excitability of a cortical neuronal population represents a finely tuned balance between excitation and inhibition. Slight alterations of the efficacy of inhibition may lead to greater changes in the collective behavior of a population of cells.