Neuropeptide Y-like immunoreactivity is absent from most perivascular noradrenergic axons in a marsupial, the brush-tailed possum

Noradrenergic perivascular axons were demonstrated in all systemic arteries and veins of a marsupial, the brush-tailed possum (Trichosurus vulpecula), by a catecholamine fluorescence procedure and with antisera directed against the catecholamine-synthesizing enzymes tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DβH). Perivascular axons with neuropeptide Y-like immunoreactivity (NPY-LI) were not found in most systemic arteries and veins using antisera which recognize NPY and other members of the pancreatic polypeptide family in diverse vertebrate species. The exceptions were the renal, coeliac, main mesenteric and iliac arteries, where up to 50% of axons with TH-LI or DβH-LI also showed NPY-LI with two of the 4 antisera used. No noradrenergic nerve cell bodies in thoracic sympathetic ganglia had NPY-LI, whilst 3% of noradrenergic nerve cell bodies in lumbar sympathetic chain ganglia had weak NPY-LI. This marsupial is the first vertebrate species found to date in which the majority of perivascular noradrenergic axons do not contain NPY-LI. If these axons contain an as yet unidentified neuropeptide, it is unlikely to be closely related to NPY.