Medial hypothalamic stimulation suppresses nociceptive spinal dorsal horn neurons but not the tail-flick reflex in the rat

E. S. Culhane, Earl Carstens

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


This study investigated the potential analgesic effects of medial hypothalamic stimulation (HS) on a measure of nocifensive behavior (tail-flick test (TF)) in awake rats, and potential inhibitory effects of identical HS on spinal dorsal horn neuronal responses to noxious skin heating in the same animals anesthetized with sodium pentobarbital. Sixty-five male Sprague-Dawley rats implanted with a bipolar stimulation electrode in histologically verified medial hypothalamic sites were tested behaviorally for TF suppression during HS (100 ms trains at 100 Hz, 3/s, 100-1100 μA) in 2-4 consecutive weekly test sessions. Thirty-three of these rats were then used in electrophysiological experiments to record responses of 36 dorsal horn units to noxious skin heating (48-54 °C, 10 s/2 min) of the hindfoot pad in the absence of and during HS. Behaviorally, 31 65 rats had no TF suppression at the highest HS intensity tested (1100 μA). 24 65 rats exhibited aversive behavior or motor activity which disallowed reliable TF testing, and only 10 65 rats showed TF suppression in at least one test session. In electrophysiological experiments, the heat-evoked responses of 25 36 dorsal horn units were inhibited to at least 50% of control during HS. The responses of 11 units remained at 65-100% of the control responses during HS of up to 1100 μA. In rats demonstrating TF suppression, 4 7 units were inhibited. In rats with no TF suppression, 10 15 units were inhibited, and in rats showing aversive behavior, 11 14 units were inhibited by HS. These data indicate that although HS suppresses spinal nociceptive neurons, it does not cause reliable TF suppression in unanesthetized rats and bring into question the often-held assumption that stimulation-evoked descending inhibition of spinal nociceptive neurons implies behavioral analgesia.

Original languageEnglish (US)
Pages (from-to)137-144
Number of pages8
JournalBrain Research
Issue number1-2
StatePublished - Jan 12 1988


  • Descending inhibition
  • Dorsal horn neuron
  • Heat-evoked response
  • Medial hypothalamus
  • Rat
  • Stimulation-produced analgesia
  • Tail-flick reflex

ASJC Scopus subject areas

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


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