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The Journal of Neuroscience, July 4, 2007, 27(27):7344-7360; doi:10.1523/JNEUROSCI.0873-07.2007

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Behavioral/Systems/Cognitive
Catecholaminergic Control of Mitogen-Activated Protein Kinase Signaling in Paraventricular Neuroendocrine Neurons In Vivo and In Vitro: A Proposed Role during Glycemic Challenges

Arshad M. Khan,¹ Todd A. Ponzio,² Graciela Sanchez-Watts,¹ B. Glenn Stanley,^2,3 Glenn I. Hatton,² and Alan G. Watts¹

¹Neuroscience Research Institute and Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-2520, and ²Department of Cell Biology and Neuroscience and ³Department of Psychology, University of California, Riverside, California 92521

Correspondence should be addressed to Dr. Arshad M. Khan, Neuroscience Research Institute and Department of Biological Sciences, University of Southern California, 3641 Watt Way, Hedco Neuroscience Building, MC 2520, Los Angeles, CA 90089-2520. Email: arshadk{at}usc.edu

Paraventricular hypothalamic (PVH) corticotropin-releasing hormone (CRH) neuroendocrine neurons mount neurosecretory and transcriptional responses to glycemic challenges [intravenous 2-deoxyglucose (2-DG) or insulin]. Although these responses require signals from intact afferents originating from hindbrain CA (catecholaminergic) neurons, the identity of these signals and the mechanisms by which they are transduced by PVH neurons during glycemic challenge remain unclear. Here, we tested whether the prototypical catecholamine, norepinephrine (NE), can reproduce PVH neuroendocrine responses to glycemic challenge. Because these responses include phosphorylation of p44/42 mitogen-activated protein (MAP) kinases [extracellular signal-regulated kinases 1/2 (ERK1/2)], we also determined whether NE activates ERK1/2 in PVH neurons and, if so, by what mechanism.

We show that systemic insulin and 2-DG, and PVH-targeted NE microinjections, rapidly elevated PVH phospho-ERK1/2 levels. NE increased Crh and c-fos expression, together with circulating ACTH/corticosterone. However, because injections also increased c-Fos mRNA in other brain regions, we used hypothalamic slices maintained in vitro to clarify whether NE activates PVH neurons without contribution of inputs from distal regions. In slices, bath-applied NE triggered robust phospho-ERK1/2 immunoreactivity in PVH (including CRH) neurons, which attenuated markedly in the presence of the ₁ adrenoceptor antagonist, prazosin, or the MAP kinase kinase (MEK) inhibitor, U0126 (1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene). Therefore, at a systems level, local PVH delivery of NE is sufficient to account for hindbrain activation of CRH neuroendocrine neurons during glycemic challenge. At a cellular level, these data provide the first demonstration that MAP kinase signaling cascades (MEKERK) are intracellular transducers of noradrenergic signals in CRH neurons, and implicate this transduction mechanism as an important component of central neuroendocrine responses during glycemic challenge.

Key words: ERK1; ERK2; p44/42 MAP kinases; MEK; PVH; parvicellular; CRH; neuroendocrine; norepinephrine; catecholamine; ₁ adrenoceptor; signal transduction; stress; hypoglycemia; stimulus–response coupling

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Received Feb. 26, 2007; revised May 30, 2007; accepted May 31, 2007.

Correspondence should be addressed to Dr. Arshad M. Khan, Neuroscience Research Institute and Department of Biological Sciences, University of Southern California, 3641 Watt Way, Hedco Neuroscience Building, MC 2520, Los Angeles, CA 90089-2520. Email: arshadk{at}usc.edu

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