The ENK^{RVM →SRD} Projection Constitutes a Functionally Specific Circuit for Bidirectional Pain Modulation

Area of Science:

• Neuroscience
• Pain Research
• Molecular Biology

Background:

• Chronic pain management faces challenges due to limited effective therapies with severe side effects.
• The rostral ventromedial medulla (RVM) is crucial for pain modulation, but its neuronal subpopulations are not fully understood.

Purpose of the Study:

• To identify neurochemical identities and functional roles of RVM neuronal subpopulations involved in pain modulation.
• To elucidate the descending pain-inhibitory circuits originating from the RVM.

Main Methods:

• Utilized mouse models of inflammatory (CFA) and neuropathic (CCI) pain.
• Employed in situ hybridization, chemogenetics, optogenetics, and in vivo electrophysiology.
• Conducted behavioral experiments to assess pain, anxiety, and motor function.

Main Results:

• Identified enkephalinergic (ENK) neurons in the RVM projecting to the subnucleus reticularis dorsalis (SRD) as a distinct descending pain-inhibitory circuit.
• Observed elevated ENK RVM neuron activity in pain models.
• Demonstrated that activating the ENK RVM→SRD pathway elevates pain thresholds and reverses hyperalgesia, while inhibition induces hyperalgesia.
• Confirmed selective modulation of nociception without affecting anxiety or motor function.

Conclusions:

• The ENK RVM→SRD pathway represents a novel, bidirectional descending circuit for pain inhibition.
• This pathway holds significant potential as a therapeutic target for developing new analgesics.