Assembly and Maintenance of GABAergic Synapses

Understanding the mechanisms underlying Axon Growth and Guidance is key to finding the root cause of neurological diseases and discovering potential therapies.

In this important study, researchers TrkB is required for the localization of an Ig superfamily cell adhesion molecule, Contactin-1, in Golgi and granule cells and the absence of Contactin-1 also results in deficits in inhibitory synaptic development. This demonstrates that TrkB controls the assembly and maintenance of GABAergic synapses and suggest that TrkB functions, in part, through promoting synaptic adhesion: TrkB (Tropomyosin-Related Kinase B) Controls the Assembly and Maintenance of GABAergic Synapses in the Cerebellar Cortex. The Journal of Neuroscience, February 23, 2011 • 31(8):2769 –2780 • 276

Contactin-1 IHC and WB

Images: Inactivation of TrkB kinase activity disrupts the localization of GABAergic synaptic proteins. A–I, Homozygous mice carrying TrkB F616A allele were treated with water or 1NMPP1 from P0 to P28 and analyzed at P28. The localization of GAD65 (green; B), GAD67 (green; E) and gephyrin (red; H ) in the IGL is reduced in TrkB F616A mice treated with 1NMPP1 compared with TrkB F616A mice treated with water (A, D, G). C, F, I, Quantification of the area ratio of GAD65:vGluT1 (C), GAD67:vGluT1 (F ) and gephyrin:vGluT1 expression (I) in control and 1NMPP1-treated mice. J–R, Homozygousmice carrying TrkB F616A allele were treated with water or 1NMPP1 from P30 to P50 and analyzed at P50. The localization of GAD65 (green; K ), GAD67 (green; N ) and gephyrin (red; Q) is reduced in TrkB F616A mice treated with 1NMPP1 compared with control (J, M, P). L, O, R, Quantification of the area ratio of GAD65:vGluT1 (L), GAD67:vGluT1 (O) and gephyrin:vGluT1 expression (R) in control and 1NMPP1-treated mice. Scale bar, 10 um.

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

Diabetes and Obesity Research

Antibodies

Diabetes and Obesity Proteins