Schizophrenia, autism and intellectual disabilities are best understood as spectrums of diseases that have broad sets of causes. However, it is becoming evident that these conditions also have overlapping phenotypes and genetics, which is suggestive of common deficits. In this context, the idea that the disruption of inhibitory circuits might be responsible for some of the clinical features of these disorders is gaining support. Recent studies in animal models demonstrate that the molecular basis of such disruption is linked to specific defects in the development and function of interneurons - the cells that are responsible for establishing inhibitory circuits in the brain. These insights are leading to a better understanding of the causes of schizophrenia, autism and intellectual disabilities, and may contribute to the development of more-effective therapeutic interventions.

The mammalian telencephalon is considered the most complex of all biological structures. It comprises a large number of functionally and morphologically distinct types of neurons that coordinately control most aspects of cognition and behavior. The subpallium, for example, not only gives rise to multiple neuronal types that form the basal ganglia and parts of the amygdala and septum but also is the origin of an astonishing diversity of cortical interneurons. Despite our detailed knowledge on the molecular, morphological, and physiological properties of most of these neuronal populations, the mechanisms underlying their generation are still poorly understood. Here, we comprehensively analyzed the expression patterns of several transcription factors in the ventricular zone of the developing subpallium in the mouse to generate a detailed molecular map of the different progenitor domains present in this region. Our study demonstrates that the ventricular zone of the mouse subpallium contains at least 18 domains that are uniquely defined by the combinatorial expression of several transcription factors. Furthermore, the results of microtransplantation experiments in vivo corroborate that anatomically defined regions of the mouse subpallium, such as the medial ganglionic eminence, can be subdivided into functionally distinct domains.

Neuroscience produces a vast amount of data from an enormous diversity of neurons. A neuronal classification system is essential to organize such data and the knowledge that is derived from them. Classification depends on the unequivocal identification of the features that distinguish one type of neuron from another. The problems inherent in this are particularly acute when studying cortical interneurons. To tackle this, we convened a representative group of researchers to agree on a set of terms to describe the anatomical, physiological and molecular features of GABAergic interneurons of the cerebral cortex. The resulting terminology might provide a stepping stone towards a future classification of these complex and heterogeneous cells. Consistent adoption will be important for the success of such an initiative, and we also encourage the active involvement of the broader scientific community in the dynamic evolution of this project.

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