Tail-flick related activity in medullospinal neurons

Horacio Vanegas, Nicholas M. Barbaro, Howard L. Fields

Research output: Contribution to journalArticlepeer-review

121 Scopus citations


Using the classification system of Fields et al.16 131 neurons in the rostral ventromedial medulla (RVM) of lightly anesthetized rats were divided into 3 groups according to their response during tail-flick (TF) testing: those with an abrupt increase in activity prior to TF (on-cells); those with a sudden pause in activity prior to TF (off-cells); those with no change in activity prior to TF (neutral cells). Collision testing was performed using a cervical spinal cord stimulating electrode to determine whether these neurons projected to the cord. Conduction velocities were determined for all cord-projecting neurons. All 3 cell types projected to the cord and approximately 38% of cord-projecting neurons were flick-related (off-or on-cells). All projecting neurons were within or immediately adjacent to the nucleus raphe magnus. The mean conduction velocity of on-cell axons (17.7 m/s) was significantly greater than that of off-cell axons (10.7 m/s) and neutral cell axons (12.4 m/s). Conduction velocities for all cells were within the range for myelinated axons. These findings support the hypothesis16 that off- and on-cells in the RVM play a significant role in pain modulation at the spinal cord level.

Original languageEnglish (US)
Pages (from-to)135-141
Number of pages7
JournalBrain research
Issue number1
StatePublished - Oct 29 1984


  • analgesia
  • collision test
  • nucleus raphe magnus
  • rat
  • spinal cord

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology

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