Phenylethanolamine N-Methyltransferase-Immunoreactive Neurons in the Medulla oblongata of the Pigeon (Columba livia) Projecting to the Hypothalamic Paraventricular Nucleus

Abstract

The distribution and ascending projections to the hypothalamic paraventricular nucleus of phenylethanolamine N-methyltransferase (PNMT)-immunoreactive perikaria were studied in adult pigeons using a combination of retrograde transport of Fluorogold injected into the paraventricular nucleus, and double immunohistochemical procedures for PNMT, tyrosine hydroxylase and neuropeptide Y. PNMT-immunoreactive cell bodies were found in the subtrigeminal reticular nucleus of the ventrolateral medulla and in the nucleus of the solitary tract, mainly in the subnuclei: medialis superficialis, pars posterior, and medialis ventralis, pars posterior. PNMT-immunoreactive perikaria were also tyrosine hydroxylase immunoreactive, and are located within the rostral tyrosine hydroxylase immunoreactive cell groups of these areas. No perikaria double-labeled for neuropeptide Y and PNMT were found. Retrograde labeled cell bodies were observed in the subtrigeminal reticular nucleus and in the nucleus of the solitary tract. PNMT-immunoreactive retrogradely labeled cells were mainly observed in the subtrigeminal reticular nucleus. These data suggest the presence in the pigeon of medullary adrenergic cell groups partially comparable to mammalian C1 and C2 groups. Comparison of these results with data previously obtained in amphibians and reptiles suggests that the presence of a hypothalamically-projecting C1-like group might be a plesiomorphic medullary attribute in amniotes, whereas the variable presence of C2 and C3-like groups, as well as the content of NPY in the putative adrenergic perikaria, seem to be species-specific.