Local and commissural neuropeptide‐containing projections of the nucleus of the solitary tract to the dorsal vagal complex in the pigeon

Abstract

The neuropeptide content of neurons of the nucleus of the solitary tract (NTS), which have local and commissural projections to the dorsal motor nucleus of the vagus (DMNX) and to NTS, were demonstrated in the pigeon (Columba livia) by using a combined fluorescein-bead retrograde-transport-immunofluorescence technique. The specific peptides studied were bombesin, cholecystokinin, enkephalin, galanin, neuropeptide Y, neurotensin, and substance P. Perikarya immunoreactive for bombesin were located in medial tier subnuclei of NTS and the caudal NTS. Most galanin- and substance P-immunoreactive cells were found in subnucleus medialis ventralis. Cells immunoreactive for neuropeptide Y were found in the medial tier of NTS and in the lateral tier, especially in subnucleus lateralis dorsalis intermedius. The majority of enkephalin- and neurotensin-immunoreactive cells were found centrally in subnuclei medialis dorsalis and medialis intermedius. Cells immunoreactive for cholecystokinin were located in subnuclei lateralis dorsalis pars anterior, medialis superficialis, and the caudal NTS. Based on the presence of retrogradely labeled cells, numerous neurons of the medial tier of NTS, but extremely few lateral tier NTS neurons, had projections to the ipsilateral and contralateral DMNX and NTS. The number of retrogradely labeled NTS cells was always greater ipsilaterally than contralaterally. The percentages of peptide-immunoreactive NTS cells that projected to the ipsilateral and contralateral DMNX were in the ranges of 29-61% and 10-48%, respectively. The percentages of peptide-immunoreactive NTS cells that projected to the contralateral NTS ranged from 13 to 60%. Peptide-immunoreactive NTS cells that have local and commissural projections to DMNX and NTS may act as interneurons in vagovagal reflex pathways and in the integration of visceral sensory and forebrain input to NTS and DMNX.

Distribution of neurotensin-containing neurons in the central nervous system of the pigeon and the chicken

“…In the pigeon and chicken, the dorsal vagal complex has the same distribution of NT-containing neurons and fibers, and, in particular, immunoreactive fibers are present at the highest density found in the brains of these birds. The results in the pigeon are in agreement with those in previous studies (Berk et al, 1993a,b,;Berk and Smith, 1994). The distribution of immunoreactive neurons in birds is similar to that in the rat, in that the NT-containing neurons are located in the nucleus of the solitary tract, and immunoreactive fibers are present in the dorsal motor nucleus of the vagus nerve (Higgins et al, 1984).…”

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

“…These cells were observed in various NTS subnuclei including the mVp, that contains PNMT-IR hypothalamically projecting neurons. As stated by Berk and Smith [1994], colchicine treatment is a procedure necessary for NPY-IR cell body detection in the NTS, enhancing peptide visualization by disrupting microtubules, increasing mRNAencoding neuropeptides, or even inducing NPY mRNA in neurons that normally do not express it [Cortés et al, 1990]. Further, colchicine treatment induces long lasting increases in cFos expression in ventrolateral and NTS medullary neurons immunoreactive to TH and PNMT; this persists 24 h after colchicine treatment, in a pattern of distribution similar to that induced by immobilization stress [Ceccatelli et al, 1989].…”

“…However, NPY-IR perikaria were found in the NTS of pigeons treated with an intracerebroventricular injection of colchicine 36 hours before perfusion [Berk and Smith, 1994]. These cells were observed in various NTS subnuclei including the mVp, that contains PNMT-IR hypothalamically projecting neurons.…”

“…It is thus conceivable that the present absence of medullary NPY perikaria could be due to intracellular NPY levels that are below the detection limit of the technique. However, we cannot exclude the possibility that NPY is normally not synthesized by a large number of the NPY-IR cells found in colchicine-treated pigeons [Berk and Smith, 1994], and is produced by them only in some specific physiological or pharmacological conditions. Although there is evidence from various vertebrate taxa for a widespread distribution and possibly a conservative evolution of both NPY [Hoyle, 1999] and the prosencephalic circuits containing this peptide in vertebrates [Anderson and Reiner, 1990], it is still unknown whether NPY and PNMT are coexpressed in medullary neurons projecting to the hypothalamus of birds, as found in mammals.…”

Molecular cloning and characterization of avian bombesin‐like peptide receptors: new tools for investigating molecular basis for ligand selectivity

“…The effectiveness of GRP upon intracerebroventricular injection suggested that this peptide localized not only in the peripheral endocrine organ, as demonstrated earlier by immunohistochemistry, but also in brain. In fact, Vaillant et al (1979) found substantial quantities of BN-like immunoreactivity in turkey brain; Cassone & Moore (1987) reported the existence of BN-like reactivity in the suprachiasmatic region of house sparrow and Berk & Smith (1994) described projection of BN-immunoreactive cells to the vagal complex of the pigeon. More recently, Dubbeldam & den Boer-Visser (2000) studied in detail the distribution of GRP immunoreactivity in the brain of the dove.…”