Wednesday, September 15, 2010

TRHR1 and LepRb receptors and Thermogenesis

I would like to thank Montina Van Meter, Lab Manager, Autonomic Neuroscience at Pennington Biomedical Research Center, for alerting me to this just published study. Included are excellent images of stained LepRb (OB-Rb) and GAD1 expressing neurons localized in loose clusters of cells in the DMN, NST, and the VLM.

This study focus on identifying loci in the hindbrain where leptin and TRH act synergistically to increase thermogenesis. Since thermogenic processes are at the root of how our bodies regulate energy, understanding the related expression and signaling pathways could be key to finding therapies for obesity.

Maria J. Barnes, Richard C. Rogers, Montina J. Van Meter and Gerlinda E. Hermann. Co-localization of TRHR1 and LepRb receptors on neurons in the hindbrain of the rat. doi:10.1016/j.brainres.2010.07.094

Example images: Distribution of LepRb+ fibers in hindbrain. LepRb-ir (red) fibers and varicosities are seen among TRHR1-ir (green) cells and fibers. These red and green fibers are adjacent and co-mingle but do not show co-localization of receptors. This pattern is seen in (A) fascicles of the solitary tract (ST); (B) raphe pallidus (RP), and (C) raphe obscurrus (RO). (D) Border between the medial solitary nucleus (NST) and the area postrema (AP; white dashed line) showing an abundance of LepRb-ir (red) fibers and
 neurons (white arrows for selected neurons) in the NST but not the AP. (E) LepRb-ir staining is suppressed by pretreatment of tissue with LepRb epitope blocking peptide. (F) TRHR1-ir staining is suppressed by treatment with excess TRHR1. Scale bar A–D=100 microns; E, F=300 microns. cc=central canal.
Abstract: We have reported a highly cooperative interaction between leptin and thyrotropin releasing hormone (TRH) in the hindbrain to generate thermogenic responses (Hermann et al., 2006) (Rogers et al., 2009). Identifying the locus in the hindbrain where leptin and TRH act synergistically to increase thermogenesis will be necessary before we can determine the mechanism(s) by which this interaction occurs. Here, we performed heat-induced epitope recovery techniques and in situ hybridization to determine if neurons or afferent fibers in the hindbrain possess both TRH type 1 receptor and long-form leptin receptor [TRHR1; LepRb, respectively]. LepRb receptors were highly expressed in the solitary nucleus [NST], dorsal motor nucleus of the vagus [DMN] and catecholaminergic neurons of the ventrolateral medulla [VLM]. All neurons that contained LepRb also contained TRHR1. Fibers in the NST and the raphe pallidus [RP] and obscurrus [RO] that possess LepRb receptors were phenotypically identified as glutamatergic type 2 fibers (vglut2). Fibers in the NST and RP that possess TRHR1 receptors were phenotypically identified as serotonergic [i.e., immunopositive for the serotonin transporter; SERT]. Co-localization of LepRb and TRHR1 was not observed on individual fibers in the hindbrain but these two fiber types co-mingle in these nuclei. These anatomical arrangements may provide a basis for the synergy between leptin and TRH to increase thermogenesis.

Related Reagents:
Leptin and Leptin Receptor Antibodies
Leptin Proteins

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