Classifying neuronal subclasses of the cerebellum through constellation 1 pharmacology 2 3

22 A pressing need in neurobiology is the comprehensive identification and 23 characterization of neuronal subclasses within the mammalian nervous system. To 24 this end we used constellation pharmacology as a method to interrogate the 25 neuronal and glial subclasses of the mouse cerebellum individually and 26 simultaneously. We then evaluated the data obtained from constellation-27 pharmacology experiments by cluster analysis to classify cells into neuronal and 28 glial subclasses, based on their functional expression of glutamate, acetylcholine, 29 and GABA receptors, among other ion channels. Conantokin peptides were 30 employed to identify NMDA receptor subtypes, which revealed that neurons of the 31 young mouse cerebellum expressed NR2A and NR2B NMDA receptor subunits. 32 Additional pharmacological tools disclosed differential expression of AMPA 33 receptors, nicotinic acetylcholine receptors, and muscarinic acetylcholine receptors 34 in different neuronal and glial subclasses. Certain cell subclasses correlated with 35 known attributes of granule cells, and we combined constellation pharmacology 36 with genetically labeled neurons to identify and characterize Purkinje cells. This 37 study illustrates the utility of applying constellation pharmacology to classify 38 neuronal and glial subclasses in specific anatomical regions of the brain.