Fig. 4: The stimulatory effect of GLP-1 in the OB on insulin secretion is mediated by a decrease in sympathetic nervous system activity.

a Pancreatic NA levels of RD and WD mice after Ex4 injection in the OB (n = 9 mice in total, p-value _treatment = 0.0054). The dataset includes four groups: NaCl OB RD (n = 2), NaCl OB WD (n = 3), Ex4 OB RD (n = 2) and Ex4 OB WD (n = 2). For NaCl OB RD, the values are as follows: minimum = 555.9, 25th percentile = 555.9, median = 665.2, 75th percentile = 774.5 and maximum = 774.5. For NaCl OB WD, the values are: minimum = 303.5, 25th percentile = 303.5, median = 376.8, 75th percentile = 469.6 and maximum = 469.6. For Ex4 OB RD, the values are: minimum = 285.4, 25th percentile = 285.4, median = 337.8, 75th percentile = 390.2 and maximum = 390.2. For Ex4 OB WD, the values are: minimum = 13.49, 25th percentile = 13.49, median = 25.98, 75th percentile = 38.46 and maximum = 38.46. Data were analysed using ordinary two-way ANOVA followed by Fisher’s LSD pairwise comparisons. b Schematic illustration of bilateral OB injections of Ex4 combined with IP administration of UK14304 followed by an OGTT in OB-cannulated WD mice. The creation of this figure includes elements inspired by the style used in Montaner et al. ¹⁶. c OGTT tests preceded by an IP injection of UK14304 and an OB injection of Ex4 in OB-cannulated WD after 20 weeks under WD (n = 8; p-value OGTT treatment = 0.0047) (left). AUC of glycaemia (right); p-value AUC NaCl IP - NaCl OB vs. NaCl IP - Ex4 OB = 0.0159; p-value AUC NaCl IP - Ex4 OB vs. UK14304 IP - Ex4 OB = 0.0490. OGTT data were analysed using RM two-way ANOVA and AUCs by using RM one-way ANOVA followed by Bonferroni. d Plasma insulin levels of OB-cannulated WD during OGTT tests preceded with OB-injected Ex4 and IP injected UK14304 (RM two-way ANOVA followed by Bonferroni; n = 8; p-value t15 NaCl IP - NaCl OB vs. NaCl IP - Ex4 OB = 0.0313; p-value t15 NaCl IP - Ex4 OB vs. UK14304 IP - Ex4 OB = 0.0324; p-value t30 NaCl IP - NaCl OB vs. NaCl IP - Ex4 OB = 0.0078; p-value t30 NaCl IP - Ex4 OB vs. UK14304 IP - Ex4 OB = 0.0055). e Strategy to deliver Ex4 or vehicle in the OB of OB-cannulated C57BL6 mice prior to cFos counting in the MCL (f) or LH (g). The creation of this figure includes elements inspired by the style used in Montaner et al. ¹⁶. f Representative photomicrographs of cFos immunoreactivity and automated cell counting in the MCL using CellProfiler (left), scale bar: 200 µm. cFos density in the MCL after Ex4 or vehicle injection in the OB of WD mice (right). Data are expressed as cFos+ nuclei/mean MCL area of all mice. Data were analysed using two-sided unpaired Student’s t test (n = 5; p-value = 0.0401). g Representative photomicrographs of cFos immunoreactivity in the LH (left). cFos density in the LH after Ex4 or saline injection in the OB of WD mice (right). Data are expressed as cFos+ nuclei/mean LH area of all mice. Data were analysed using two-sided unpaired Student’s t test (n = 4; p-value = 0.0227). h Schematic illustration of unilateral Alexa 488-conjugated cholera toxin B subunit (CTB_green) delivery in the LH for retrograde tracing of the primary olfactory cortex. The creation of this figure includes elements inspired by the style used in Montaner et al. ¹⁶. i Coronal sections of the LH after unilateral injection of CTB_green (left). CTB staining in the primary olfactory cortex (right). LH lateral hypothalamus, AHP anterior hypothalamus – posterior part, VMH ventromedial hypothalamus, 3V third ventricle, AON anterior olfactory nucleus, VTT ventral tenia tecta, VON ventral olfactory nucleus, PC piriform cortex, OT olfactory tubercle. Structure boundaries were drawn based on Franklin and Paxinos mouse brain atlas. Scale bar: 200 µm (left) and 100 µm (right). Four biological replicates were conducted, obtaining similar results. j Schematic illustration of viral delivery in the OB and bilateral cannula placement in the PVN of Glp1r-Cre WD mice followed by OGTTs. The creation of this figure includes elements inspired by the style used in Montaner et al.¹⁶. k OGTT tests preceded with an IP injection of CNO in Glp1r^OBhM3Dq WD PVN-cannulated mice after 20 weeks under WD (26-week old; n = 10; p-value OGTT _treatment = 0.0019) (left). The black square and the green line indicate Bicuculline and CNO delivery, respectively, before the glucose gavage (t0). AUC of glycaemia (right; p-value NaCl PVN - NaCl IP vs. NaCl PVN - CNO IP = 0.0013; p-value NaCl PVN - CNO IP vs. Bic PVN - NaCl IP = 0.0213; p-value NaCl PVN - CNO IP vs. Bic PVN - CNO IP = 0.0446). OGTT data were analysed using RM two-way ANOVA and AUCs by using RM one-way ANOVA, both followed by Bonferroni post-hoc tests. l Plasma insulin levels of Glp1r^OBhM3Dq WD PVN-cannulated mice after CNO IP injection (RM two-way ANOVA followed by Bonferroni, n = 10; p-value t15 NaCl PVN - NaCl IP vs. NaCl PVN - CNO IP < 0.0001; p-value t15 NaCl PVN - CNO IP vs. Bic PVN - CNO IP < 0.0001). Data are given as mean ± SEM. *p < 0.05; **p < 0.01; ***p < 0.001; ns not significant. Source data are provided as a Source Data file.