Imbalanced Innervation of the Hypothalamic Paraventricular Nucleus by the AgRP and α-Melanocyte-Stimulating Hormone Axonal Projections in Germ-Free Mice.

Abstract

Introduction: Innervation of the paraventricular nucleus of the hypothalamus (PVN) by the orexigenic agouti-related protein (AgRP) and anorexigenic α-melanocyte-stimulating hormone (α-MSH) neurons of the arcuate nucleus (ARC) is a key element in the appetite-regulating neuronal circuitry whose development is influenced by circulating metabolic signals. In the present work, we studied if PVN innervation by the AgRP and α-MSH fibers is influenced by gut microbiota.

Methods: To this aim, we compared, using immunohistochemistry, the innervation of PVN by AgRP and α-MSH fibers between germ-free and specific pathogen-free 7-week-old female mice.

Results: We found that germ-free mice display an increased innervation of the PVN by both AgRP and α-MSH fibers, but also that the increase in AgRP fiber density was about twice as pronounced as that of α-MSH.

Conclusion: These data reveal that gut microbiota plays a modulatory role in the development of the ARC/PVN axonal projections. An imbalance between AgRP and α-MSH innervation in germ-free mice may contribute to their metabolic and behavioral alterations.