Neuropeptide Y acts in the paraventricular nucleus to suppress sympathetic nerve activity and its baroreflex regulation

Key points Neuropeptide Y (NPY) acts in the brain to decrease sympathetic nerve activity (SNA); however, the specific site is unknown. We identify the paraventricular nucleus of the hypothalamus (PVN) as a site of action, since nanoinjection of NPY into the PVN dose-dependently decreases SNA, whereas PVN injection of NPY Y1 and Y5 receptor antagonists increases SNA. NPY may directly inhibit PVN presympathetic neurons, since these neurons express Y1 receptors and, in patch-clamp experiments, are inhibited by NPY. Our data also indicate that identified PVN presympathetic neurons that are inhibited by NPY are also excited by α-melanocyte-stimulating hormone. These results identify endogenous PVN NPY as a novel and potent inhibitory neuromodulator that may contribute to changes in SNA that occur in states associated with altered energy balance, such as obesity and pregnancy. Abstract Neuropeptide Y (NPY), a brain neuromodulator that has been strongly implicated in the regulation of energy balance, also acts centrally to inhibit sympathetic nerve activity (SNA); however, the site and mechanism of action are unknown. In chloralose-anaesthetized female rats, nanoinjection of NPY into the paraventricular nucleus of the hypothalamus (PVN) dose-dependently suppressed lumbar SNA (LSNA) and its baroreflex regulation, and these effects were blocked by prior inhibition of NPY Y1 or Y5 receptors. Moreover, PVN injection of Y1 and Y5 receptor antagonists in otherwise untreated rats increased basal and baroreflex control of LSNA, indicating that endogenous NPY tonically inhibits PVN presympathetic neurons. The sympathoexcitation following blockade of PVN NPY inhibition was eliminated by prior PVN nanoinjection of the melanocortin 3/4 receptor inhibitor SHU9119. Moreover, presympathetic neurons, identified immunohistochemically using cholera toxin b neuronal tract tracing from the rostral ventrolateral medulla (RVLM), express NPY Y1 receptor immunoreactivity, and patch-clamp recordings revealed that both NPY and α-melanocyte-stimulating hormone (α-MSH) inhibit and stimulate, respectively, PVN–RVLM neurons. Collectively, these data suggest that PVN NPY inputs converge with α-MSH to influence presympathetic neurons. Together these results identify endogenous NPY as a novel and potent inhibitory neuromodulator within the PVN that may contribute to changes in SNA that occur in states associated with altered energy balance, such as obesity and pregnancy.