Citation

We recently demonstrated that exogenous and endogenous Neuropeptide Y (NPY) decreases sympathetic nerve activity and baroreflex function via an action on Y1 receptors (Y1R) in the hypothalamic paraventricular nucleus (PVN). However, whether NPY acts directly on presympathetic neurons projecting to the rostral ventrolateral medulla (RVLM) is unknown. To test this hypothesis, we used immunofluorescence to determine if Y1R are present in PVN neurons that project to RVLM, identified by prior RVLM microinjection of the retrograde tracer cholera toxin subunit B (CTb, 0.25%; List Laboratories). NPY Y1R-immunoreactivity (ir) (1:100; Santa Cruz; n=4) was found in scattered neurons in multiple PVN parvocellular subdivisions, including the dorsal, medial, lateral, and ventrolateral subnuclei. NPY Y1R-ir was also prominent in the PVN posterior magnocellular subnucleus. In separate experiments, NPY Y1R-ir colocalized with vasopressin-ir (1:800; gift of H. Gainer) in neurons in this region. While no colocalization of NPY Y1R-ir with CTb-ir (1:1000; AbCam) was observed in the more rostral PVN (1.6 mm from bregma), a significant fraction (1638%) of NPY Y1R neurons in caudal PVN regions (1.8 to 2.1 mm from bregma) co-expressed CTb. In summary, NPY Y1R are expressed in PVN neurons projecting to the RVLM, suggesting that NPY acts directly on these neurons to inhibit sympathetic nerve activity and baroreflex regulation. Supported in part by HL088552.