Neurons responding to electrical stimulation of the SCN region are primarily GABAergic in nature. a Left shows a schematic of the recording configuration for experiments using SCN electrical and optogenetic stimulation of target cells in GAD2+/cre; Ai32+/− slices. Pie charts show proportions unresponsive (upper) and optogenetically activated (lower) target cells showing varying classes of response to electrical stimulation (n.r. indicates no response to electrical stimulation; difference in proportions analysed by χ2 test, P = 0.03). Right plot shows proportions of neurons showing optogenetic activation as a function of position on the dorsal-ventral axis. b–e Peri-stimulus rasters for representative cells showing response to optogenetic stimulation (left) and SCN electrical stimulation (right), under baseline conditions and following GABAA receptor blockade (BIC; 20 μm (+)-bicuculline) in the absence and presence of ionotropic glutamate receptor antagonists (iGlu-X; 50 μm D-AP5 and 20 μm CNQX). Panels respectively show examples of neurons classed as GABA inhibited (b), Mixed (c), GABA activated (d) and Glu. activated (e) based on response to SCN electrical stimulation and effects of antagonist treatments. Raw data values used for statistical analysis can be found in Additional file 8.