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865.23/MM24 Stimulus-, circuit- and intracellular-level determinants
of MAP kinase and CREB activation in parvicellular hypothalamic paraventricular
A M Khan, K L Rapp, T A Ponzio, G Sanchez-watts, A G Watts
featuring IT-03 Anti-DBH-SAP (Poster; Wednesday, Nov 19, 2008, 3:00 PM - 4:00 PM)
Systemic insulin or 2-deoxyglucose (2-DG) rapidly elevate phosphorylated MAP
kinases (phospho-ERK1/2) and/or CRH hnRNA in PVHp neurons, and increase circulating
ACTH and corticosterone. These neuroendocrine responses are likely driven by
hindbrain-originating catecholaminergic (CA) neuron subpopulations, which richly
innervate the PVHp and are activated by glycemic challenges. Supporting this,
acute in vivo or in vitro PVH delivery of the prototypical catecholamine, norepinephrine
(NE), recapitulates these responses (J Neurosci, 2007, 27:7344-7360). Here,
we determined whether PVHp ERK/CREB phosphorylation responses require: 1) intact
CA afferents, when triggered by three distinct in vivo challenges; and 2) upstream
MEK kinase activity, when triggered by NE application in acute hypothalamic
slices maintained in vitro.
Methods. Rats given PVH microinjections of anti-dopamine-b-hydroxylase (DBH)-saporin antibody-toxin conjugate (DSAP) or mIgG-saporin control conjugate received either normal 0.9% saline vehicle or one of three systemic challenges: insulin (2 U/kg, i.v.); 2-DG (250 mg/kg, i.v.); or hypertonic saline (1.5 M, i.p.) and sacrificed 30 min later. Brains were processed for CRH mRNA/hnRNA hybridization, or DBH, phospho-ERK or phospho-CREB immunocytochemistry. Plasma was collected for hormone determinations at 0 and 30 min. In separate in vitro studies, acute hypothalamic slices received either no treatment (controls), or received bath-applied NE (100 mM) in the presence or absence of the MEK inhibitor, U0126 (10 mM), or the inactive MEK inhibitor analogue, U0124 (10 mM). Ten min later, slices were placed in fixative.
Results. 1. Sham-lesioned animals: Relative to vehicle, all challenges elevated phospho-ERK1/2, phospho-CREB, and ACTH/corticosterone levels; and, except for insulin, also increased CRH hnRNA. 2. Lesioned animals: DSAP treatment selectively destroyed hindbrain-originating CA afferents. In insulin- and, to a lesser extent, 2-DG-treated animals, this loss was accompanied by markedly reduced PVH phospho-ERK1/2 and circulating ACTH/corticosterone. In contrast, these responses remained robust in CA-deafferented hypertonic saline-treated rats. Phospho-CREB levels were differentially reduced relative to phospho-ERK in lesioned rats. 3. Slices: NE-induced PVH elevations of phosphorylated ERK1/2 and CREB were reduced markedly by U0126, but not U0124, pre-treatment.
Conclusions. PVHp phospho-ERK selectively couples to CA afferents during glycemic challenges and ERK/CREB recruitment appears to require MEK activity.