title: Galanin-immunoreactivity identifies a distinct population of inhibitory interneurons in laminae I-III of the rat spinal cord.
abstract: BACKGROUND
  Inhibitory interneurons constitute 30-40% of neurons in laminae I-III and have an important anti-nociceptive role. However, because of the difficulty in classifying them we know little about their organisation. Previous studies have identified 3 non-overlapping groups of inhibitory interneuron, which contain neuropeptide Y (NPY), neuronal nitric oxide synthase (nNOS) or parvalbumin, and have shown that these differ in postsynaptic targets. Some inhibitory interneurons contain galanin and the first aim of this study was to determine whether these form a different population from those containing NPY, nNOS or parvalbumin. We also estimated the proportion of neurons and GABAergic axons that contain galanin in laminae I-III.
  
  
  RESULTS
  Galanin cells were concentrated in laminae I-IIo, with few in laminae IIi-III. Galanin showed minimal co-localisation with NPY, nNOS or parvalbumin in laminae I-II, but most galanin-containing cells in lamina III were nNOS-positive. Galanin cells constituted ~7%, 3% and 2% of all neurons in laminae I, II and III, and we estimate that this corresponds to 26%, 10% and 5% of the GABAergic neurons in these laminae. However, galanin was only found in ~6% of GABAergic boutons in laminae I-IIo, and ~1% of those in laminae IIi-III.
  
  
  CONCLUSIONS
  These results show that galanin, NPY, nNOS and parvalbumin can be used to define four distinct neurochemical populations of inhibitory interneurons. Together with results of a recent study, they suggest that the galanin and NPY populations account for around half of the inhibitory interneurons in lamina I and a quarter of those in lamina II.
authors.affiliation: College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ UK. andrew.todd@glasgow.ac.uk
authors.forename: Sheena Y X
authors.initials: SY
authors.lastname: Tiong
authors.forename: Erika
authors.initials: E
authors.lastname: Polgár
authors.forename: Josie C
authors.initials: JC
authors.lastname: van Kralingen
authors.forename: Masahiko
authors.initials: M
authors.lastname: Watanabe
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Todd
mesh_terms: D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D019004:Galanin / Q000378:metabolism*; D007150:Immunohistochemistry; D007395:Interneurons / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D009433:Neural Inhibition / Q000502:physiology*; D009478:Neuropeptide Y / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism; D010320:Parvalbumins / Q000378:metabolism; D020671:Posterior Horn Cells / Q000166:cytology / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000166:cytology*; D013194:Staining and Labeling; D050495:Vesicular Inhibitory Amino Acid Transport Proteins / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D009478:Neuropeptide Y; D010320:Parvalbumins; C118623:Slc32a1 protein, rat; D050495:Vesicular Inhibitory Amino Acid Transport Proteins; D005680:gamma-Aminobutyric Acid; D019004:Galanin; D052248:Nitric Oxide Synthase Type I; D015740:Calcitonin Gene-Related Peptide