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Presentation
Postsynaptic spinal mu opioid receptor-expressing neurons are required for morphine anti-hyperalgesia
American Pain Society/ The Journal of Pain (2007)
  • Robert H. Kline, IV, University of Kentuc
Abstract
Lumbar intrathecal (i.t.) injection of Dermorphin-saporin (500 ng) in rats
has been shown to selectively destroy spinal cord dorsal horn neurons
expressing the mu-opioid receptor (MOR) with resulting attenuation of
antinociceptive effects of systemic and i.t. morphine to low intensity (44
C) but not high (52 C) heat and increased responding in the formalin
test. The current study examined the effects of lumbar i.t. Derm-sap on
morphine antinociception during capsaicin-induced thermal hyperalgesia
and in the formalin test. Effects of Derm-sap on primary afferent
thermal nociceptors were assessed in baseline hotplate and tail flick
testing and after systemic loperamide, a peripherally restricted mu opioid.
Sixteen male rats and twenty female rats received a single lumbar
intrathecal injection of 10 ul of PBS or Derm-sap (500 ng). Sensitivity to
mu opioids was evaluated on the 44 C hotplate test under baseline
conditions in the female rats and three hours after topical plantar capsaicin
cream (0.94%) in the male rats. Effects of morphine (10 mg/kg, s.c.)
on formalin behavior (25 ul of 5%) was evaluated in female rats for 90
min after plantar formalin injection. Immunohistochemical staining for
GIRK2, a postsynaptic potassium channel essential for morphine analgesia,
was evaluated in lumbar dorsal horns of PBS and Derm-sap rats.
Derm-sap produced: 1) no change in baseline tail flick responses, 2)
reduced antinociceptive effects of systemic morphine in the 44 C hotplate
test after plantar capsaicin; 3) reduced antinociceptive effects of
systemic morphine, but not loperamide, in the 44 C hotplate test; 4)
reduced antinociceptive effects of morphine in the formalin test and 4)
decreased GIRK2 staining in the dorsal horn. These observations demonstrate
an important role for dorsal horn MOR-expressing neurons in
analgesic and anti-hyperalgesic actions of morphine.
Publication Date
April, 2007
Location
Washington DC
Citation Information
Robert H. Kline. "Postsynaptic spinal mu opioid receptor-expressing neurons are required for morphine anti-hyperalgesia" American Pain Society/ The Journal of Pain (2007)
Available at: http://works.bepress.com/robert-kline/5/