Fig. 4: Excitation of septal GLU neurons is reinforcing and SuM neurons monosynaptically excites septal GLU neurons.

a Schematic showing septal site of AAV injection and optic fiber placement in WT, vGat-, vGlut2-, and ChAt-Cre mice. b Example histology of ChR2-eYFP expression in the septum and optic fiber placements (yellow dotted outline) for the 4 strains of mice used. Scale bar = 100 µm. See Supplementary Fig. 5 for all results (n = 48). c Active lever-press (mean − SEM) per session per group: WT (n = 10), vGat- (n = 18), vGlut2- (n = 12), and ChAt-Cre (n = 6) mice. *pWT vs vGat = 0.0008, pWT vs ChAt = 0.0071, and pvGlut2 vs vGat = 0.0077 and pvGlut2 vs ChAt = 0.0397 (Tukey post hoc HSD test). d Schematic showing an injection of the retrograde vector into the MS of the vGlut2-Cre mouse. e, f Photomicrogram showing retrogradely labeled glutamatergic (GLU) cells in green and non-GLU cells in red. n = 4 mice. Scale bars = 200 µm. Abbreviations: cc, corpus callosum; DBB, diagonal band of Broca; fr, fasciculus retroflexus; LS, lateral septum; ml, medial lemniscus; MM, medial mammillary nucleus; MS, medial septum; PH, posterior hypothalamic region; SHi, septohippocampal nucleus; VStr, ventral striatum. g Schematic showing injection preparation for ex vivo brain slice electrophysiology experiments to determine whether SuM vGlut2 neurons can monosynaptically excite septal vGlut2 neurons. h Top row shows an example of a septum neuron expressing Td-tomato, and therefore glutamatergic, surrounded by ChR2-eYFP fibers, the image was taken before patch-clamp electrophysiology of this neuron. Bottom row shows example histology of the septal area with Td-tomato positive cells localized primarily to MS and SuM:SeptvGlut2 terminals innervating the septal complex. Scale bar top = 10 µm, bottom = 200 µm. i Average EPSP traces from recorded septum neurons. Traces are calculated from average responses of cells at the midpoint of data sets. Postsynaptic response is abolished by GLU antagonists. Blue rectangle represents approximately 2 ms blue-light laser stimulation. j EPSP amplitude data of septum neurons. Data are mean + SEM with individual data points (circles; 2–4 cells per mouse, n = 4). At least 1 Tomato + and − was recorded per mouse. k Effect of GLU antagonists on EPSP amplitude. Data are mean − SEM with individual data points. **p = 0.01, paired t-test. See (j) for n’s. l EPSP latency responses after the onset of blue-light pulse. Data are mean ± SEM with individual data points. See (j) for n’s. Source data are provided as a Source Data file.