Spinal microglia are required for long-term maintenance of neuropathic pain

Area of Science:

• Neuroscience
• Pain Research
• Immunology

Background:

• Spinal microglia contribute to neuropathic pain initiation.
• The role of spinal microglia in maintaining chronic pain is not well understood.
• Chronic pain involves complex signaling pathways beyond initial inflammation.

Purpose of the Study:

• To investigate the persistence and therapeutic potential of spinal microglia in chronic neuropathic pain.
• To differentiate between early inflammatory and late maintenance mechanisms of pain hypersensitivity.
• To identify distinct therapeutic targets for acute versus chronic pain.

Main Methods:

• Rodent model of nerve injury-induced neuropathic pain.
• Selective depletion of spinal microglia using Mac1-saporin immunotoxin.
• Blockade of brain-derived neurotrophic factor (BDNF)-TrkB signaling via intrathecal TrkB Fc chimera.
• Assessment of pain hypersensitivity and synaptic activity in the spinal dorsal horn.

Main Results:

• Microglia activation in the spinal cord persisted for over 3 months post-nerve injury.
• Selective spinal microglia depletion and TrkB Fc chimera treatment almost completely reversed chronic pain hypersensitivity.
• Cytokine inhibition did not reverse established pain hypersensitivity.
• Spinal microglia depletion did not affect nociception or synaptic activity in control animals.

Conclusions:

• Persistent spinal microglia-neuron interactions maintain chronic neuropathic pain.
• Therapeutic strategies targeting spinal microglia or BDNF-TrkB signaling can reverse established pain.
• Distinct central signaling pathways underlie pain maintenance compared to early inflammatory responses, offering different treatment targets.