Neuropeptide Y immunoreactivity in cutaneous sympathetic and sensory neurons during development of the guinea pig

Different levels of the cutaneous vasculature are innervated selectively by subpopulations of sympathetic neurons distinguished by the presence or abs ence of immunoreactivity (-IR) for neuropeptide Y (NPY). This study used mu ltiple-labelling immunohistochemistry to examine the appearance of NPY-IR i n neurons innervating cutaneous vessels in the ear pinna of embryonic, feta l, and neonatal guinea pigs. NPY-immunoreactive axons were detected in the ear bud at embryonic day 25. However, these axons lacked IR for tyrosine hy droxylase (TH) and often ran in bundles with substance P (SP)-immunoreactiv e axons close to the epidermis. Many neuronal somata in the cervical dorsal root ganglia (DRG) at late embryonic stages contained NPY-IR with or witho ut SP-IR, but no NPY-IR was detected in DRG or subepidermal axons by late f etal stages. IR for calcitonin gene-related peptide increased in DRG neuron s from midfetal to late fetal stages, after the decrease in NPY-IR. Populat ions of TH-IR neurons with or without NPY-IR were present in the superior c ervical ganglion (SCG) from midembryonic stages. TH-immunoreactive axons we re not detected in the ear pinna until midfetal stages, when axons with TH- IR and NPY-IR innervated proximal arteries arid TH-immunoreactive axons wit hout NPY-IR innervated distal vessels. Vasoactive intestinal peptide-IR was detected transiently in most fetal SCG neurons with TH-IR and NPY-IR but w as not detected in cutaneous axons. These results demonstrate that selectiv e expression of NPY by subpopulations of sympathetic neurons occurs prior t o innervation of their targets. This suggests that target contact is not re quired to establish appropriate patterns of expression of peptide neurotran smitters by cutaneous sympathetic neurons. J. Comp. Neurol. 437: 321-334, 2 001. (C) 2001 Wiley-Liss, Inc.