A quantitative study of brainstem projections from lamina I neurons in the cervical and lumbar enlargement of the rat

Brain Res. 2010 Jan 13;1308(5):58-67. doi: 10.1016/j.brainres.2009.10.041. Epub 2009 Oct 23.


Lamina I of the rat spinal cord contains neurons that project to various brain areas including thalamus, periaqueductal grey matter (PAG), lateral parabrachial area (LPb), caudal ventrolateral medulla and a region in dorsal medulla that includes the nucleus tractus solitarius and dorsal reticular nucleus. We have shown that spinothalamic lamina I neurons are infrequent in rat lumbar enlargement, where they constitute approximately 5% of the estimated 400 projection neurons on each side of the L4 segment (Al-Khater and Todd, 2009). They are more numerous in cervical enlargement, but the total number of lamina I projection neurons in this region was not known. Here we have used paired injections of retrograde tracers into the brainstem to estimate the number of lamina I projection cells in the C7 segment. Our results suggest that there are approximately 215 lamina I projection cells per side, and that spinothalamic cells therefore make up approximately 42% of this population. The proportion of lamina I projection neurons labelled from PAG is higher in cervical than lumbar enlargement, while the proportion labelled from dorsal medulla is similar in the two regions. We also found that lamina I cells in L4 that project to the dorsal medulla are included in the population retrogradely labelled from LPb, thus confirming the estimate that there are around 400 lamina I projection cells in this segment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Afferent Pathways / physiology
  • Animals
  • Brain Stem / physiology*
  • Cell Count
  • Fluorescent Antibody Technique
  • Fluorescent Dyes
  • Male
  • Microscopy, Confocal
  • Neuronal Tract-Tracers
  • Neurons / physiology*
  • Rats
  • Rats, Wistar
  • Spinal Cord / physiology*
  • Spinothalamic Tracts / physiology
  • Thalamus / physiology*


  • Fluorescent Dyes
  • Neuronal Tract-Tracers