Pain and the primate thalamus.

Area of Science:

• Neuroscience
• Pain Research
• Spinal Cord Research

Background:

• Pain signals travel via spinothalamic tract (STT) and spinotrigeminothalamic tracts (vSTT) to the thalamus.
• Lesions in somatosensory pathways cause significant loss of neurons and inhibitory GABAergic circuitry in thalamic nuclei.
• This circuitry disruption may explain abnormal thalamic neuron activity in central deafferentation pain.

Purpose of the Study:

• To investigate the potential of selectively eliminating noxious stimulus (NS) neurons in the dorsal horn for chronic pain treatment.
• To evaluate the efficacy and impact of SSP-saporin toxin on NS neurons in non-human primates.

Main Methods:

• Development of SSP-saporin toxin targeting substance P receptors on NS neurons.
• Administration of SSP-saporin to the lumbar spinal cord in monkeys.
• Assessment of lesions in NS neurons and changes in the animals' response to noxious stimuli.
• Analysis of thalamic inhibitory circuitry following SSP-saporin treatment.

Main Results:

• SSP-saporin effectively lesioned NS neurons in the monkey lumbar spinal cord.
• Treatment reduced the animals' response to noxious cutaneous stimuli.
• SSP-saporin treatment affected a small subset of neurons projecting to the thalamus.
• Crucially, no significant changes in the thalamus's inhibitory circuitry were observed.

Conclusions:

• Selective elimination of NS neurons using SSP-saporin is a viable strategy for pain management.
• This targeted approach avoids the detrimental effects on thalamic inhibitory circuitry seen with broader pathway lesions.
• SSP-saporin offers a promising therapeutic avenue for chronic pain by preserving crucial neural networks.