pubmed.ncbi.nlm.nih.gov

GLP-1 receptor stimulation of the lateral parabrachial nucleus reduces food intake: neuroanatomical, electrophysiological, and behavioral evidence - PubMed

GLP-1 receptor stimulation of the lateral parabrachial nucleus reduces food intake: neuroanatomical, electrophysiological, and behavioral evidence

Jennifer E Richard et al. Endocrinology. 2014 Nov.

Abstract

The parabrachial nucleus (PBN) is a key nucleus for the regulation of feeding behavior. Inhibitory inputs from the hypothalamus to the PBN play a crucial role in the normal maintenance of feeding behavior, because their loss leads to starvation. Viscerosensory stimuli result in neuronal activation of the PBN. However, the origin and neurochemical identity of the excitatory neuronal input to the PBN remain largely unexplored. Here, we hypothesize that hindbrain glucagon-like peptide 1 (GLP-1) neurons provide excitatory inputs to the PBN, activation of which may lead to a reduction in feeding behavior. Our data, obtained from mice expressing the yellow fluorescent protein in GLP-1-producing neurons, revealed that hindbrain GLP-1-producing neurons project to the lateral PBN (lPBN). Stimulation of lPBN GLP-1 receptors (GLP-1Rs) reduced the intake of chow and palatable food and decreased body weight in rats. It also activated lPBN neurons, reflected by an increase in the number of c-Fos-positive cells in this region. Further support for an excitatory role of GLP-1 in the PBN is provided by electrophysiological studies showing a remarkable increase in firing of lPBN neurons after Exendin-4 application. We show that within the PBN, GLP-1R activation increased gene expression of 2 energy balance regulating peptides, calcitonin gene-related peptide (CGRP) and IL-6. Moreover, nearly 70% of the lPBN GLP-1 fibers innervated lPBN CGRP neurons. Direct intra-lPBN CGRP application resulted in anorexia. Collectively, our molecular, anatomical, electrophysiological, pharmacological, and behavioral data provide evidence for a functional role of the GLP-1R for feeding control in the PBN.

PubMed Disclaimer

Figures

Figure 1.
Figure 1.

GLP-1 innervation of the PBN. Fluorescent YFP-PPG neurons (green) and DAPI (nuclear stain, blue) in coronal sections through the PBN and the NTS of YFP-PPG mice. Micrographs showing the cell bodies of green YFP-immunoreactive PPG neurons (yellow arrows) in the NTS (A and B). Micrographs showing the lPBN (C and D), and the region of the mPBN just below the superior cerebellar peduncles (scp) (E and F). Many green YFP-immunoreactive axons closely appose blue DAPI-labeled cell bodies in the lPBN. White arrows indicate PBN cell bodies closely apposed by the GLP-1 fibers, whereas red arrows indicate cell bodies in this region that were not apposed by the GLP-1 fibers. Insets in B, D, and F show the interaction at a single cell level. cc, central canal. B, D, and F show higher magnification of areas in A, C, and D, respectively.

Figure 2.
Figure 2.

GLP-1R stimulation by Ex-4 in the lPBN reduces food intake and body weight. Intra-lPBN delivery of Ex-4 reduced the consumption of chocolate pellets over the 2-hour period of data collection (A), the amount of saccharine drank (but not water consumption) over 4 hours of data collection (B), the 24-hour chow intake (C), and 24-hour body weight change (D). Data are expressed as mean ± SEM. *, P < .05; **, P < .01; ***, P < .005. E, Representative photomicrograph of a coronal section of rat brain at the level of the lPBN illustrating the microinjection site (encircled area) for the behavioral experiments (left panel) and a schematic representation of the PBN (right panel). scp, superior cerebellar peduncles; 4th V, 4th ventricle.

Figure 3.
Figure 3.

GLP-1R blockade in the lPBN increases food intake and body weight. Intra-lPBN delivery of Ex-9 increased chow intake at 2 and 3 hours after injection (A). Overnight chow intake measured at 16 hours after Ex-9 injection was not altered (B). Ex-9 increased 16-hour body weight gain. C, Data are expressed as mean ± SEM. *, P < .05.

Figure 4.
Figure 4.

Loose-patch clamp recordings of action currents in the neurons of the external lPBN. Application of GLP-1R agonist Ex-4 (1μM) in the extracellular solution increased the firing rate (A and B). Extracellular administration of the GLP-1R antagonist Exendin-9(9-39) (Ex-9) (1μM), blocked this effect of Ex-4 (C and D). Histogram shows the relative percentages of firing rate after application of Ex-4 with and without Ex-9 (E). Central GLP-1R stimulation by lateral ventricle injection of Ex-4 increased c-Fos activation in the PBN. Quantified immunoreactivity of Fos-positive neurons in the PBN after Ex-4 treatment in ad libitum-fed rats (F) and representative images of the c-Fos study (G). Data are expressed as mean ± SEM. c-Fos data were expressed as average of total c-Fos count of all rats; total number per rat was calculated by adding total number of c-Fos-positive cells from the left and right lPBN. Each electrophysiological experimental group contained 10 recorded cells from 6–7 animals. *, P < .05. scp, superior cerebellar peduncles; VEH, vehicle.

Figure 5.
Figure 5.

Gene expression after central GLP-1R stimulation. In ad libitum-fed rats, GLP-1R activation by Ex-4 increased the mRNA expression of the gene that encodes CGRP (Calca), without significantly changing the mRNA expression of other genes previously shown to be associated with changes in food intake in the PBN (A). In overnight-fasted rats, Ex-4 did not significantly change the mRNA expression of any of the genes measured (B). Ex-4 increased the expression of IL6 (but not IL1β), central mediators of GLP-1R-induced anorexia in both ad libitum-fed (C) and fasted (D) rats. Data are expressed as mean ± SEM. **, P < .01.

Figure 6.
Figure 6.

GLP-1 innervation of CGRP neurons in the lPBN. Many YFP-immunoreactive axons (green) closely apposed the CGRP neurons (red) of the lPBN. Yellow arrows indicate CGRP-labeled lPBN cell bodies closely apposed by the GLP-1 fibers, whereas white arrows indicate CGRP-labeled cell bodies in this region that were not apposed by the GLP-1 fibers. B, Higher magnification of the lPBN region presented in A. Inset in B shows the interaction at a single cell level. Blue color represents DAPI the nuclear stain. Nearly half of the CGRP-positive cells in the lPBN receive GLP-1 innervation (C), and most cells in the lPBN that were innervated by GLP-1 fibers were CGRP-positive (D).

Figure 7.
Figure 7.

CGRP reduces food intake via a direct action in lPBN. Intra-lPBN delivery of CGRP reduced chow consumption up to 2 hours after injections (A). This effect was short lasting, because chow intake (B) and body weight (C) measured 16 hours after injections were not altered. Data are expressed as mean ± SEM. *, P < .05.

Figure 8.
Figure 8.

Graphical summary of results. Collectively, our data reveal the lPBN as a neural substrate for the feeding and body weight suppression effect of GLP-1 and identify the mechanisms involved. Elements of this novel energy balance relevant circuit identified in the current study are indicated in red. In contrast to the excitatory GLP-1 projections to the PBN, the projections from the hypothalamus (green) to the PBN provide inhibitory inputs, and their activation results in an orexigenic response.

Similar articles

Cited by

References

    1. Holst JJ. The physiology of glucagon-like peptide 1. Physiol Rev. 2007;87(4):1409–1439. - PubMed
    1. Rinaman L. Ascending projections from the caudal visceral nucleus of the solitary tract to brain regions involved in food intake and energy expenditure. Brain Res. 2010;1350:18–34. - PMC - PubMed
    1. Llewellyn-Smith IJ, Reimann F, Gribble FM, Trapp S. Preproglucagon neurons project widely to autonomic control areas in the mouse brain. Neuroscience. 2011;180:111–121. - PMC - PubMed
    1. Turton MD, O'Shea D, Gunn I, et al. A role for glucagon-like peptide-1 in the central regulation of feeding. Nature. 1996;379(6560):69–72. - PubMed
    1. Schick RR, Zimmermann JP, vorm Walde T, Schusdziarra V. Peptides that regulate food intake: glucagon-like peptide 1-(7-36) amide acts at lateral and medial hypothalamic sites to suppress feeding in rats. Am J Physiol Regul Integr Comp Physiol. 2003;284(6):R1427–R1435. - PubMed

Publication types

MeSH terms

Substances