title: A quantitative study of neurochemically defined excitatory interneuron populations in laminae I-III of the mouse spinal cord.
abstract: BACKGROUND
  Excitatory interneurons account for the majority of neurons in laminae I-III, but their functions are poorly understood. Several neurochemical markers are largely restricted to excitatory interneuron populations, but we have limited knowledge about the size of these populations or their overlap. The present study was designed to investigate this issue by quantifying the neuronal populations that express somatostatin (SST), neurokinin B (NKB), neurotensin, gastrin-releasing peptide (GRP) and the γ isoform of protein kinase C (PKCγ), and assessing the extent to which they overlapped. Since it has been reported that calretinin- and SST-expressing cells have different functions, we also looked for co-localisation of calretinin and SST.
  
  
  RESULTS
  SST, preprotachykinin B (PPTB, the precursor of NKB), neurotensin, PKCγ or calretinin were detected with antibodies, while cells expressing GRP were identified in a mouse line (GRP-EGFP) in which enhanced green fluorescent protein (EGFP) was expressed under control of the GRP promoter. We found that SST-, neurotensin-, PPTB- and PKCγ-expressing cells accounted for 44%, 7%, 12% and 21% of the neurons in laminae I-II, and 16%, 8%, 4% and 14% of those in lamina III, respectively. GRP-EGFP cells made up 11% of the neuronal population in laminae I-II. The neurotensin, PPTB and GRP-EGFP populations showed very limited overlap, and we estimate that between them they account for ~40% of the excitatory interneurons in laminae I-II. SST which is expressed by ~60% of excitatory interneurons in this region, was found in each of these populations, as well as in cells that did not express any of the other peptides. Neurotensin and PPTB were often found in cells with PKCγ, and between them, constituted around 60% of the PKCγ cells. Surprisingly, we found extensive co-localisation of SST and calretinin.
  
  
  CONCLUSIONS
  These results suggest that cells expressing neurotensin, NKB or GRP form largely non-overlapping sets that are likely to correspond to functional populations. In contrast, SST is widely expressed by excitatory interneurons that are likely to be functionally heterogeneous.
authors.affiliation: Institute of Neuroscience and Psychology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK.
authors.forename: Maria
authors.initials: M
authors.lastname: Gutierrez-Mecinas
authors.affiliation: Department of Morphological Brain Science, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Furuta
authors.affiliation: Department of Anatomy, Hokkaido University School of Medicine, Sapporo, Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Watanabe
authors.affiliation: Institute of Neuroscience and Psychology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK andrew.todd@glasgow.ac.uk.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Todd
mesh_terms: D000818:Animals; D064032:Calbindin 2 / Q000378:metabolism; D019886:Gastrin-Releasing Peptide / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007395:Interneurons / Q000737:chemistry*; D008297:Male; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D009479:Neuropeptides / Q000378:metabolism*; D009496:Neurotensin / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism; D013004:Somatostatin / Q000378:metabolism; D066148:Spinal Cord Dorsal Horn / Q000378:metabolism*; D015320:Tachykinins / Q000378:metabolism
chemical_list: D064032:Calbindin 2; D009479:Neuropeptides; D011498:Protein Precursors; D015320:Tachykinins; C485184:enhanced green fluorescent protein; C044206:preprotachykinin; D049452:Green Fluorescent Proteins; D009496:Neurotensin; D013004:Somatostatin; D019886:Gastrin-Releasing Peptide; C087857:protein kinase C gamma; D011493:Protein Kinase C
keywords: Dorsal horn; gastrin-releasing peptide; neurokinin B; neurotensin; somatostatin