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Abstract
<p class="first" id="P1">Phoenixin (PNX) is a 14-amino acid amidated peptide (PNX-14)
or an N-terminal extended
20-residue amidated peptide (PNX-20) recently identified in neural and non-neural
tissue. Mass spectrometry analysis identified a major peak corresponding to PNX-14,
with negligible PNX-20, in mouse spinal cord extracts. Using a previously characterized
antiserum that recognized both PNX-14 and PNX-20, PNX-immunoreactivity (irPNX) was
detected in a population of dorsal root ganglion (DRG) cells and in cell processes
densely distributed to the superficial layers of the dorsal horn; irPNX cell processes
were also detected in the skin. The retrograde tracer, Fluorogold, injected subcutaneously
(s.c.) to the back of the cervical and thoracic spinal cord of mice, labeled a population
of DRG, some of which were also irPNX. PNX-14 (2, 4 and 8 mg/kg) injected s.c.to the
nape of the neck provoked dose-dependent repetitive scratching bouts directed to the
back of the neck with the hindpaws. The number of scratching bouts varied from 16–95
in 30 min, commencing within 5 min post-injection and lasted 10–15 min. Pretreatment
of mice at −20 min with nalfurafine (20 µg/kg, s.c.), the kappa opioid receptor agonist,
significantly reduced the number of bouts induced by PNX-14 (4 mg/kg) compared with
that of saline-pretreated mice. Our results suggest that the peptide, PNX-14, serves
as one of the endogenous signal molecules transducing itch sensation in the mouse.
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