title: Dynorphin is expressed primarily by GABAergic neurons that contain galanin in the rat dorsal horn.
abstract: BACKGROUND
  The opioid peptide dynorphin is expressed by certain neurons in the superficial dorsal horn of the spinal cord, but little is known about the types of cell that contain dynorphin. In this study, we have used an antibody against the dynorphin precursor preprodynorphin (PPD), to reveal the cell bodies and axons of dynorphin-expressing neurons in the rat spinal cord. The main aims were to estimate the proportion of neurons in each of laminae I-III that express dynorphin and to determine whether they are excitatory or inhibitory neurons.
  
  
  RESULTS
  PPD-immunoreactive cells were concentrated in lamina I and the outer part of lamina II (IIo), where they constituted 17% and 8%, respectively, of all neurons. Around half of those in lamina I and 80% of those in lamina II were GABA-immunoreactive. We have previously identified four non-overlapping neurochemical populations of inhibitory interneurons in this region, defined by the presence of neuropeptide Y, galanin, parvalbumin and neuronal nitric oxide synthase. PPD co-localised extensively with galanin in both cell bodies and axons, but rarely or not at all with the other three markers. PPD was present in around 4% of GABAergic boutons (identified by the presence of the vesicular GABA transporter) in laminae I-II.
  
  
  CONCLUSIONS
  These results show that most dynorphin-expressing cells in the superficial dorsal horn are inhibitory interneurons, and that they largely correspond to the population that is defined by the presence of galanin. We estimate that dynorphin is present in ~32% of inhibitory interneurons in lamina I and 11% of those in lamina II. Since the proportion of GABAergic boutons that contain PPD in these laminae was considerably lower than this, our findings suggest that these neurons may generate relatively small axonal arborisations.
authors.affiliation: Institute of Neuroscience and Psychology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ UK.
authors.forename: Thomas C P
authors.initials: TC
authors.lastname: Sardella
authors.forename: Erika
authors.initials: E
authors.lastname: Polgár
authors.forename: Francesca
authors.initials: F
authors.lastname: Garzillo
authors.forename: Takahiro
authors.initials: T
authors.lastname: Furuta
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kaneko
authors.forename: Masahiko
authors.initials: M
authors.lastname: Watanabe
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Todd
mesh_terms: D000818:Animals; D004399:Dynorphins / Q000378:metabolism*; D059330:GABAergic Neurons / Q000378:metabolism*; D019004:Galanin / Q000378:metabolism; D007395:Interneurons / Q000378:metabolism; D008297:Male; D020671:Posterior Horn Cells / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000166:cytology / Q000378:metabolism
chemical_list: D011498:Protein Precursors; C036448:pre-prodynorphin; D004399:Dynorphins; D019004:Galanin