TY - JOUR T1 - Classes and continua of hippocampal CA1 inhibitory neurons revealed by single-cell transcriptomics JF - bioRxiv DO - 10.1101/143354 SP - 143354 AU - Kenneth D. Harris AU - Carolina Bengtsson Gonzales AU - Hannah Hochgerner AU - Nathan G. Skene AU - Lorenza Magno AU - Linda Katona AU - Peter Somogyi AU - Nicoletta Kessaris AU - Sten Linnarsson AU - Jens Hjerling-Leffler Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/06/28/143354.abstract N2 - Understanding any brain circuit will require a categorization of its constituent neurons. In hippocampal area CA1, at least 23 classes of GABAergic neuron have been proposed to date. However, this list may be incomplete; additionally, it is unclear whether discrete classes are sufficient to describe the diversity of cortical inhibitory neurons, or whether continuous modes of variability are also required. We studied the transcriptomes of 3663 CA1 inhibitory cells, revealing 10 major GABAergic groups that divided into 49 fine-scale clusters. All previously described and several novel cell classes were identified, with three previously-described classes unexpectedly found to be identical. A common continuous mode of variation modulated the expression of many genes, reflecting a range from metabolically highly active faster-spiking cells that proximally target pyramidal cells, to slower-spiking cells that target distal dendrites or interneurons. Within classes, cells showed further variability along the continuum and this correlated with their spiking phenotype. Surprisingly, several cell types previously described as discrete classes represented ranges along this continuum. These results elucidate the complexity of inhibitory neurons in one of the simplest cortical structures, and show that characterizing these cells requires continuous modes of variation as well as discrete cell classes. ER -