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“Gamma-aminobutyric acid-containing (GABAergic) interneurons play an important role in the function of the cerebral cortex. Through mostly inhibitory mechanisms, interneurons control hyperexcitability, and synchronize and shape the spatiotemporal dynamics of cortical activity underlying various GDC-0449 datasheet brain functions. Their influence on cortical function is remarkably diverse, a reflection of the large variety of interneuronal populations that exist in the mammalian cortex. Research over the past few years has rapidly transformed our understanding of their mechanisms underlying the generation of different classes of interneurons. In this review, we summarize recent progress on this

process, progress which holds the promise of providing a rational framework for their classification, as well as means to understand their role in cortical processing. The cerebral cortex consists of two main classes of neurons, pyramidal

cells and interneurons, which respectively use glutamate and γ-aminobutyric acid (GABA) as main neurotransmitters. In the adult cortex, pyramidal cells are excitatory while GABA-containing (GABAergic) interneurons are typically inhibitory. Increasing evidence suggests that disruption of the excitatory–inhibitory balance maintained by pyramidal cells and interneurons is linked to the etiology of several neurological disorders (Rubenstein & Merzenich, 2003; Dani et al., 2005; Levitt, 2005; Lewis et al., 2005). Conversely, genes associated with such disorders have been shown to influence the development of PI3K inhibitor cortical interneurons (Erbel-Sieler et al.,

2004; Flames et al., 2007; Fazzari Racecadotril et al., 2010; Wen et al., 2010). Thus, disruption of GABAergic inputs to pyramidal cells might represent a common pathophysiological mechanism underlying multiple neuropsychiatric conditions. Interneurons comprise ∼20–30% of the cortical neuronal population and are locally projecting cells that control and synchronize the output of pyramidal neurons. Interestingly, the influence of GABAergic interneurons on pyramidal cells is largely dependent on the subcellular location of their inputs, which varies among different interneuron subtypes. Despite years of research, however, it is still unclear how many different types of cortical interneurons actually exist. This is due, among other reasons, to the difficulties that are inherent to the task of defining what a cortical interneuron is (Ascoli et al., 2008). Despite some reservations, today it is largely accepted that distinct types of interneurons exist; they are defined by a constellation of neurochemical, anatomical and electrophysiological characteristics. Based on this definition, several major classes of interneurons have been identified, although many other types of interneurons are left out of this major classification.