Preparation of Brain Slices

Frontiers in Neural Circuits www.frontiersin.org May 2010 | Volume 4 | Article 12 | 1 clature for morphological, physiological and molecular features was agreed upon by the Petilla Interneuron Nomenclature Group (Ascoli et al., 2008). Among GABAergic interneurons, those expressing the neuropeptide somatostatin (SOM) are particularly heterogeneous in their molecular, morphological and electrophysiological features (Sabo and Sceniak, 2006). To better understand this variability, we took advantage of a transgenic mouse line where SOM-positive neurons are labeled with GFP (Oliva et al., 2000) to explore if subtypes of SOM interneurons could be distinguished objectively. 59 SOM-positive interneurons from mouse primary somatosensory, frontal and visual cortex were quantitatively characterized using their morphological properties measured from reconstructions of biocytin-fi lled cells and their intrinsic electrophysiological properties, measured from whole cell recordings. Unsupervised cluster analysis revealed a group comprised of the well-known Martinotti cells, as well as two other sub-groups of SOM-positive neurons that, to our knowledge, have not yet been described. The electrophysiological classifi cation agreed well with, and thus confi rmed, the morphological classifi cation. Furthermore, signifi cant differences in axon morphology and fi ring properties between the three groups suggest that the two novel subtypes and Martinotti cells could serve different functional roles in the cortical circuit.