Received for publication January 20, 2006.
Revised March 19, 2006.
Accepted for publication March 23, 2006.

The Phenotypic Differentiation of Locus Coeruleus Noradrenergic Neurons Mediated by BDNF is Enhanced by Corticotropin Releasing Factor through the Activation of a cAMP-dependent Signaling Pathway

Abstract

We have developed a model system of locus coeruleus (LC) neurons in culture, in which brain-derived neurotrophic factor (BDNF) induces the emergence of noradrenergic neurons attested by the presence of tyrosine hydoxylase (TH) and dopamine--hydroxylase and the absence of phenylethanolamine N-methyl-transferase. Although inactive in itself, the neuropeptide corticotropin releasing factor (CRF) strongly amplified the effect of BDNF, increasing the number of cells expressing TH and the active accumulation of noradrenaline by a factor of 2-3 via a mechanism that was nonmitogenic. CRF also acted cooperatively with neurotrophin-4, which like BDNF is a selective ligand of the TrkB tyrosine kinase receptor. The effect of CRF but not that of BDNF was prevented by astressin, a non-selective CRF-1/CRF-2 receptor antagonist. However, only CRF-1 receptor transcripts were detectable in LC cultures suggesting that this receptor subtype mediated the effect of CRF. Consistent with the positive coupling of CRF-1 receptors to adenylate cyclase, the trophic action of CRF was mimicked by cAMP elevating agents. Epac a guanine nucleotide exchange factor directly activated by cAMP contributed to the effect of CRF through the stimulation of extracellular signal-regulated kinases 1/2 (ERK_1/2). However, downstream of ERK_1/2 activation by CRF, the phenotypic induction of NA neurons relied upon the stimulation of the phosphatidylinositol-3-kinase/Akt transduction pathway by BDNF. Altogether, our results suggest that CRF participates to the phenotypic differentiation of LC noradrenergic neurons during development. Whether similar mechanisms account for the high degree of plasticity of these neurons in the adult brain remains to be established.

Key words: Adrenergic, Neuropeptides, CRF, cAMP, Biogenic Amine

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