Research ArticleObesity

GABA neurons in the nucleus tractus solitarius express GLP-1 receptors and mediate anorectic effects of liraglutide in rats

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Science Translational Medicine  04 Mar 2020:
Vol. 12, Issue 533, eaay8071
DOI: 10.1126/scitranslmed.aay8071
  • Fig. 1 Knockdown of Glp1r in the NTS attenuates the food intake– and body weight–reducing effects of acutely delivered systemic liraglutide.

    (A) Mean daily body weight for AAV-GLP-1R and AAV-control rats after viral injection (day 0). Inset represents cumulative body weight change over 26 days between viral injection and sacrifice. (B) Reverse transcription PCR analysis of Glp1r expression in the NTS of AAV-GLP-1R– (n = 8) versus AAV-control–treated rats (n = 8). Inset represents histological demonstration of GFP-tagged viral expression at the caudal extent of the micropunch in a representative AAV-GLP-1R–treated rat. GAPDH, glyceraldehyde-3-phosphate dehydrogenase. (C and D) Mean cumulative chow intake and body weight change in NTS AAV-GLP-1R and AAV-control rats after vehicle (Veh) or liraglutide (Lirag; 50 μg/kg) treatment. NTS, nucleus tractus solitarius; cc, central canal. Data are expressed as means ± SEM. *P < 0.05, **P < 0.01, and ***P < 0.001 by unpaired, two-tailed Student’s t tests (A and B) and two-way repeated-measures ANOVA with Sidak’s multiple comparison tests (C and D).

  • Fig. 2 Knockdown of Glp1r in the NTS attenuates the food intake– and body weight–reducing effects of chronically delivered systemic liraglutide.

    (A) Daily HFD intake for AAV-GLP-1R (n = 10 per group) and AAV-control (n = 9 per group) rats treated with chronic daily vehicle (Veh) or liraglutide (Lirag; 200 μg/kg). (B) Mean daily HFD across 3 weeks of vehicle or liraglutide treatment compared with baseline intake (average of the 3 days before injection). (C) Daily body weight for AAV-GLP-1R and AAV-control rats treated with chronic daily vehicle or liraglutide. (D) Mean body weight across the 3 weeks of vehicle or liraglutide treatment compared with baseline intake (average of the 3 days before injection). Data are expressed as means ± SEM. *P < 0.05, **P < 0.01, and ***P < 0.001 by two-way ANOVA with Tukey’s multiple comparison tests (B and D).

  • Fig. 3 AP lesion does not attenuate liraglutide-induced food intake and body weight reduction nor c-Fos expression in the NTS.

    (A and B) Mean cumulative chow intake and body weight change in sham (n = 9) and AP-lesioned (APX; n = 11) rats after vehicle (Veh) or liraglutide (Lirag; 50 or 200 μg/kg) treatment. (C) Representative images of NTS c-Fos expression in sham and APX rats treated 90 min before sacrifice with systemic vehicle (Veh) or liraglutide (Lirag; 200 μg/kg). Red dashed lines represent the removed area postrema in APX rats. (D) Quantification of mean c-Fos+–expressing cells per NTS section in sham and APX rats treated with vehicle (Veh; n = 5 and n = 5, respectively) or liraglutide (Lirag; 200 μg/kg; n = 4 and n = 7, respectively). NTS, nucleus tractus solitarius. AP, area postrema. cc, central canal. Data are expressed as means ± SEM, *P < 0.05, **P < 0.01, and ***P < 0.001 by two-way repeated measures ANOVA with Sidak’s multiple comparison tests (A and B) or by two-way ANOVA with Tukey’s multiple comparison tests (D).

  • Fig. 4 GABAergic neurons in the NTS mediate effects of systemically delivered liraglutide on food intake and body weight.

    (A) Systemically delivered Cy3-labeled liraglutide (Cy3-Lirag; 200 μg/kg, intraperitoneally; pink) within the DVC. White box within the NTS designates area with increased magnification and three-dimensional reconstruction, pictured above, with Cy3-Lirag and DAPI-stained cell nuclei (blue). (B) FISH showing colocalization of Glp1r (red) and Gad1 (green) mRNA around cell nuclei (DAPI, blue) in the NTS. White box within the NTS designates area with increased magnification pictured above. (C) Percentage of NTS GABAergic neurons that did (GLP-1R+) and did not (GLP-1R) express the Glp1r (top) and analysis of the percentage of Glp1r mRNA–expressing cells that were (GABA+) or were not (GABA) GABA cells (bottom). (D and E) Effect of chemogenetic inhibition of GABAergic neuron signaling in the NTS via vehicle or CNO pretreatment (CNO; 1 mg/kg) on food intake and body weight after systemic liraglutide treatment (Lirag; 200 μg/kg) in GAD Cre+ rats (n = 6). (F and G) Effects of DREADD-mediated inhibition of GABAergic neuron signaling in the NTS on food intake and body weight after systemic liraglutide treatment in GAD Cre rats (n = 7) rats. GR, nucleus gracilis. Scale bar, 50 μm. Data are expressed as means ± SEM. *P < 0.05, **P < 0.01, and ***P < 0.001 by two-way repeated-measures ANOVA with Sidak’s multiple comparison tests.

Supplementary Materials

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    • Materials and Methods
    • Fig. S1. AP lesioning attenuates the food intake–reducing effects of sCT.
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