Ghrelin signaling mediates fasting-induced activation of the hypophysiotropic CRF neurons via recruitment of the NPY/AGRP/GABA neurons

ANDREOLI MF; GARCÍA ROMERO G; GIOVAMBATTISTA A; FERNANDEZ G; REY MOGGIA MA; ZUBIRÍA G; CABRAL A; REYNALDO M; TOLOSA MJ; PERELLO, MARIO

Congreso; LXIII Congreso de Sociedad Argentina de Investigación Clínica; 2018

Ghrelin is a stomach-derived hormone that acts on the growth hormone secretagogue receptor (GHSR). Plasma ghrelin increases under fasting, when it promotes appetite and activation of the hypothalamic?pituitary?adrenal (HPA) via its action on corticotropin-releasing factor (CRF) neurons of the Paraventricular nucleus (PVN). The neuronal circuits by which ghrelin regulates these actions are unclear. Here, we tested in male mice with pharmacological or genetic blockage of GHSR the effect of 48 h fasting on the PVN CRF neurons and on the neuropeptide Y (NPY)/agouti-related protein (AgRP)/GABA neurons of the arcuate nucleus (ARC), which sense plasma factors and regulate the PVN. Results: As compared to fed mice, fasted mice had an increase of the number of PVN CRF cells (3.57±0.22 fold increase, p≤0.05, T-test) and of the NPY/AgRP-fiber intensity (NPY-fibers: 0.09±0.02 vs 0.17±0.02 OD; AgRP-fibers: 3428±754 vs 10783±1490 intensity; GFP-fibers: 8558±965 vs 16799±1771 intensity in mice expressing GFP in NPY neurons, p≤0.05, T-test). As compared to wild-type (WT) mice, GHSR-deficient mice had lower levels of plasma corticosterone and the marker of neuronal activation, c-Fos, in the PVN (corticosterone: 204±30 vs 113±30 ng/ml; c-Fos: 44±9 vs 13±6 cells/side, p≤0.05, 2-way ANOVA ). Similarly, fasted mice with pharmacological blockage of GHSR showed lower c-Fos and of NPY-fiber intensity in the PVN (c-Fos:119±19 vs 177±13 cells/side; NPY-fiber: 0.21±0.01 vs 0.45±0.04 OD, p≤0.05, T-test). Fasted mice expressing tdTomato fluorescent protein in GABA neurons had more tdTomato fibers in PVN (1.36±0.08 fold increase, p≤0.05 vs fed mice, T-test). As compared to fed mice, PVN explants of fasted mice had a reduction of the basal and KCl-stimulated GABA release (basal: 4.5±0.3 vs 3.1±0.5 and KCl: 6.1±0.3 vs 4.3±0.8 % of total incorporated tracer, p≤ 0.05, 2-way ANOVA). Current results indicate that ghrelin signaling mediates fasting-induced activation of the hypophysiotropic CRF neurons via recruitment of the NPY/AGRP/GABA neurons.