Neurokinin-1 receptor-immunoreactive neurons of the ventral respiratory group in the rat

J Comp Neurol. 2001 May 28;434(2):128-46. doi: 10.1002/cne.1169.

Abstract

The rostral end of the ventral respiratory group (VRG) contains neurons that are intensely neurokinin-1 receptor (NK1R) immunoreactive (ir). It has been theorized that some of these cells might be critical to respiratory rhythmogenesis (Gray et al. [1999] Science 286:1566-1568). In the present study we determined what major transmitter these NK1R-ir cells make and whether they are bulbospinal or propriomedullary. NK1R-ir neurons were found in the VRG between Bregma levels -11.7 and -13.6 mm. The highest concentration was found between Bregma -12.3 and -13.0 mm. This region overlaps with the pre-Bötzinger complex (pre-BötC) as it was found to contain many pre-inspiratory neurons, few E2-expiratory neurons, and no I-incremental neurons. VRG NK1R-ir neurons contain neither tyrosine hydroxylase (TH) nor choline acetyl-transferase (ChAT) immunoreactivity, although dual-labeled neurons were found elsewhere within the rostral medulla. GAD67 mRNA was commonly detected in the ventrolateral medulla (VLM) but rarely in the NK1R-ir neurons of the pre-BötC region (6 % of somatic profiles). GlyT2 mRNA was commonly found in the pre-BötC region but rarely within NK1R-ir neurons (1.3 %). Up to 40% of VRG NK1R-ir neurons were retrogradely labeled by Fluoro-Gold (FG) injected in the contralateral pre-BötC region. Some NK1R-ir VRG neurons located caudal to Bregma -12.6 mm were retrogradely labeled by FG injected in the spinal cord (C4-C5, T2-T4). In sum, NK1R immunoreactivity is present in many types of ventral medullary neurons. Within the VRG proper, NK1R-ir neurons are concentrated in an area that overlaps with the pre-BötC. Within this limited region of the VRG, NK1R-ir neurons are neither cholinergic nor catecholaminergic, and very few are gamma-aminobutyric acid (GABA)ergic or glycinergic. The data suggest that most NK1R-ir neurons of the pre-BötC region are excitatory. Furthermore, the more rostral NK1R-ir cells are propriomedullary, whereas some of the caudal ones project to the spinal cord.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetylcholine / metabolism
  • Action Potentials / physiology
  • Amino Acid Transport Systems, Neutral*
  • Animals
  • Carrier Proteins / genetics
  • Catecholamines / metabolism
  • Choline O-Acetyltransferase / metabolism
  • Efferent Pathways / cytology
  • Efferent Pathways / metabolism
  • Fluorescent Dyes / pharmacokinetics
  • Glutamate Decarboxylase / genetics
  • Glycine Plasma Membrane Transport Proteins
  • Immunohistochemistry
  • Isoenzymes / genetics
  • Male
  • Medulla Oblongata / cytology
  • Medulla Oblongata / metabolism*
  • Neurons / cytology
  • Neurons / metabolism*
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Sprague-Dawley / anatomy & histology
  • Rats, Sprague-Dawley / metabolism*
  • Receptors, Neurokinin-1 / metabolism*
  • Respiratory Center / cytology
  • Respiratory Center / metabolism*
  • Respiratory Physiological Phenomena*
  • Spinal Cord / cytology
  • Spinal Cord / metabolism
  • Stilbamidines*
  • Tyrosine 3-Monooxygenase / metabolism

Substances

  • 2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt
  • Amino Acid Transport Systems, Neutral
  • Carrier Proteins
  • Catecholamines
  • Fluorescent Dyes
  • Glycine Plasma Membrane Transport Proteins
  • Isoenzymes
  • RNA, Messenger
  • Receptors, Neurokinin-1
  • Slc6a5 protein, rat
  • Stilbamidines
  • Tyrosine 3-Monooxygenase
  • Choline O-Acetyltransferase
  • Glutamate Decarboxylase
  • glutamate decarboxylase 1
  • Acetylcholine