Noradrenaline signaling in the LPBN mediates amylin's and salmon calcitonin's hypophagic effect in male rats.

The LPBN (lateral parabrachial nucleus) plays an important role in feeding control. CGRP (calcitonin gene-related peptide) LPBN neurons activation mediates the anorectic effects of different gut-derived peptides, including amylin. Amylin and its long acting analog sCT (salmon calcitonin) exert their anorectic actions primarily by directly activating neurons located in the area postrema (AP). A large proportion of projections from the AP and the adjacent nucleus of the solitary tractNTS to the LPBN, are noradrenergic (NA), and amylin-activated NAAP neurons are critical in mediating amylin's hypophagic effects. Here, we determine the functional role of NAAP amylin activated neurons to activate CGRP and non-CGRP LPBN neurons. To this end, NA was specifically depleted in the rat LPBN through a stereotaxic microinfusion of 6-OHDA, a neurotoxic agent that destroys NA terminals. While amylin (50 μg/kg) and sCT (5 μg/kg) reduced eating in sham-lesioned rats, no reduction in feeding occurred in NA-depleted animals. Further, the amylin-induced c-Fos response in the LPBN and c-Fos/CGRP colocalization were reduced in NA-depleted animals compared to controls. We conclude that AP → LPBN NA signaling, through the activation of LPBN CGRP neurons, mediates part of amylin's hypophagic effect.