title: Lamina I NK1 expressing projection neurones are functional in early postnatal rats and contribute to the setting up of adult mechanical sensory thresholds.
abstract: BACKGROUND
  A small proportion of lamina I neurons of the spinal cord project upon the hindbrain and are thought to engage descending pathways that modulate the behavioural response to peripheral injury. Early postnatal development of nociception in rats is associated with exaggerated and diffuse cutaneous reflexes with a gradual refinement of responses over the first postnatal weeks related to increased participation of inhibitory networks. This study examined the postnatal development of lamina I projection neurons from postnatal day 3 (P3) until P48.
  
  
  RESULTS
  At P3, a subset of lamina I neurons were found to express the neurokinin 1 (NK1) receptor. Using fluorogold retrograde tracing, we found that the NK1 positive neurons projected upon the parabrachial nucleus (PB) within the hindbrain. Using c-fos immunohistochemistry, we showed that lamina I and PB neurons in P3 rats responded to noxious stimulation of the periphery. Finally, ablation of lamina I neurons with substance-P saporin conjugates at P3 resulted in increased mechanical sensitivity from P45 onwards compared to control animals of the same age.
  
  
  CONCLUSIONS
  These results suggest that the lamina I pathway is present and functional at least from P3 and required for establishing and fine-tuning mechanical sensitivity in adult rats.
authors.affiliation: Department of Cell and Developmental Biology, University College London, London, WC1E 6BT, UK.
authors.forename: Sharon H W
authors.initials: SH
authors.lastname: Man
authors.forename: Sandrine M
authors.initials: SM
authors.lastname: Géranton
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Hunt
mesh_terms: D000375:Aging / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D008297:Male; D040542:Mechanotransduction, Cellular / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010812:Physical Stimulation; D020671:Posterior Horn Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018040:Receptors, Neurokinin-1 / Q000378:metabolism*; D054789:Ribosome Inactivating Proteins, Type 1 / Q000008:administration & dosage / Q000494:pharmacology; D000076985:Saporins; D012684:Sensory Thresholds / Q000187:drug effects; D013373:Substance P / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D015430:Weight Gain / Q000187:drug effects
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D018040:Receptors, Neurokinin-1; D054789:Ribosome Inactivating Proteins, Type 1; C468274:substance P-saporin; D013373:Substance P; D000076985:Saporins