Inhibition of the responses of cat dorsal horn neurons to noxious skin heating by stimulation in medial or lateral medullary reticular formation

S. Pretel, M. J. Guinan, Earl Carstens

Research output: Contribution to journalArticle

12 Scopus citations

Abstract

Responses of single lumbar dorsal horn units to noxious radiant heating (50° C, 10 s) of glabrous footpad skin were recorded in cats anesthetized with sodium pentobarbital and 70% nitrous oxide. The heat-evoked responses of 37/40 units were reduced during electrical stimulation (100 ms trains, 100 Hz, 3/s, 25-600 μA) in the medullary nucleus raphe magnus (NRM) and/or in laterally adjacent regions of the medullary reticular formation (MRF). Inhibition was elicited by stimulation in widespread areas of the medulla, but with greatest efficacy at ventrolateral sites. The magnitude of inhibition increased with graded increases in medullary stimulation intensity. Mean current intensities at threshold for inhibition or to produce 50% inhibition were higher for NRM than for MRF sites. Units' responses to graded noxious heat stimuli increased linearly from threshold (42-43° C) to 52° C. During NRM (5 units) or ipsilateral MRF stimulation (7 units), responses were inhibited such that the mean temperature-response functions were shifted toward higher temperatures with increased thresholds (1.5° and 1° C, respectively) and reduced slopes (to 60% of control). Contralateral MRF stimulation had a similar effect in 4 units. Inhibitory effects of NRM and MRF stimulation were reduced (by >25%) or abolished in 4/6 and 5/12 units, respectively, following systemic administration of the serotonin antagonist methysergide. Inhibitory effects from NRM, ipsi- and contralateral MRF were reduced or abolished in 2/9, 4/8 and 6/9 cases, respectively, following systemic administration of the noradrenergic antagonist phentolamine. These results confirm and extend previous studies of medullospinal inhibition and the role of monoamines, and are discussed in terms of analgesic mechanisms.

Original languageEnglish (US)
Pages (from-to)51-62
Number of pages12
JournalExperimental Brain Research
Volume72
Issue number1
DOIs
StatePublished - Aug 1988

Keywords

  • Descending inhibition
  • Medullary stimulation
  • Monoamines
  • Noxious heat
  • Spinal dorsal horn

ASJC Scopus subject areas

  • Neuroscience(all)

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