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Mu-opioidergic modulation differs in deep and superficial wide-dynamic range dorsal horn neurons in mice

Qian Xu1, Wei-Yan Li, Yun Guan

  • 1Department of Clinical Pharmacology, Jinling Hospital, School of Medicine, Nanjing University, Nanjing, Jiangsu 210002, China.

Neuroscience Letters
|June 11, 2013
PubMed

Insights

Morphine reduces pain signals in deep dorsal horn neurons but not superficial ones. Naloxone, however, enhances pain signals in deep neurons, suggesting distinct mu-opioid effects in different spinal cord layers.

Area of Science:

  • Neuroscience
  • Pain Research
  • Pharmacology

Background:

  • The spinal cord dorsal horn is a key site for morphine's pain-relieving effects.
  • Wide-dynamic range (WDR) neurons in the dorsal horn transmit pain signals and exhibit windup (increased excitability) after repetitive noxious stimuli.
  • Differences in mu-opioid receptor distribution and WDR neuron properties exist between superficial and deep dorsal horn layers.

Purpose of the Study:

  • To investigate the differential effects of morphine and naloxone on WDR neurons in the superficial and deep dorsal horn.
  • To explore the distinct mechanisms of mu-opioidergic modulation in different spinal cord laminae.

Main Methods:

  • Extracellular single-unit activity of WDR neurons was recorded in C57BL/6 mice.
  • Responses were compared between deep (350-700 μm) and superficial (<350 μm) dorsal horn neurons.
  • Spinal superfusion with morphine (0.5mM) and naloxone (1mM) was performed, along with electrical stimulation protocols to induce windup and assess C-component responses.

Main Results:

  • Morphine significantly decreased windup in deep WDR neurons but not superficial ones.
  • Morphine significantly depressed the steady C-component response in superficial WDR neurons only.
  • Spinal naloxone facilitated windup in deep WDR neurons but not superficial ones.

Conclusions:

  • Mu-opioidergic modulation differs between deep and superficial WDR neurons.
  • Morphine's effects on neuronal sensitization/plasticity appear specific to deep WDR neurons.
  • Morphine may inhibit acute noxious inputs to superficial WDR neurons, while affecting plasticity in deep WDR neurons.
Keywords:
MiceMu-opioid receptorWide-dynamic range neuronsWindup

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