New research from the University of Connecticut has brought the drug-free technology of electrical anaesthesia for all chronic pain sufferers a step closer.
Pain stimuli, or ‘nociceptive stimuli’ is picked up by nociceptors which send signals to the spinal cord, which passes it on to the brain where the perception of pain is manifested.
Bin Feng, associate professor in the Biomedical Engineering Department, led research which discovered how electrical stimulation of the dorsal root ganglia (DRG), sensory neural cell body clusters, can block nociceptive signal transmission to the spinal cord and prevent the brain from perceiving chronic pain signals. The findings are reported in PAIN.
Electrical devices to treat pain typically deliver electrical signals to the peripheral nervous system and spinal cord to block nociceptive signals from reaching the brain.
A major obstacle with these devices is that while some patients find them beneficial in relieving their chronic pain, others have little or no pain reduction. Despite incremental developments of neurostimulator technologies, there has not been much improvement in getting the devices to work for these patients.
“The trouble with this technology is that it can benefit a portion of patients very well, but for a larger portion of patients it has little benefit,” Prof Feng said.
One of the reasons is that such devices lag behind research into neural stimulation.
“We’re sitting on a huge pile of clinical data,” Prof Feng says. “But the science of neuromodulation remains understudied.”
Neurostimulators relieve pain according to a ‘gate control’ theory. Our bodies can detect both innocuous stimuli, like something brushing against the skin, and painful stimuli, through low- and high-threshold sensory neurons, respectively.
The spinal cord ‘gate’ can be shut by activating low-threshold sensory neurons, preventing painful nociceptive signals from high-threshold sensory neurons from crossing the spinal cord to the brain.
Neurostimulators reduce pain in patients by activating low-threshold sensory neurons with electrical pulses. This usually causes a non-painful tingling sensation in certain areas of the skin, or paresthaesia, masking the perception of pain.
Many patients receiving DRG stimulation treatment reported pain relief without the expected paraesthesia.
Seeking to understand this, Prof Feng’s lab discovered that electrical stimulation to the DRG can block transmission to the spinal cord at frequencies as low as 20 hertz. This is in contrast to previous research indicating that blocking requires kilohertz electrical stimulation.
“The cell bodies of sensory neurons form a T-junction with the peripheral and central axons in the DRG,” Feng says. “This T-junction appears to be the region that causes transmission block when DRG is stimulated.”
More remarkably, sensory nerve fibres with different characteristics are blocked by different electrical stimulation frequency ranges at the DRG, allowing the development of new neural stimulation protocols to enhance selective transmission blocking with different sensory fibre types.
“A-fibre nociceptors with large axon diameters are generally responsible for causing acute and sharp pain,” Prof Feng explained. “It is the long-lasting and dull-type pain that bothers the chronic pain patients mostIn a chronic pain condition, C-fibre nociceptors with small axon diameter and no myelin sheath play central role in the persistence of pain. Selectively blocking C-fibres while leaving A-fibres intact can be a promising strategy to target the cause of chronic pain.”
This provides evidence to place more electrodes for devices that target the DRG and surrounding neuronal tissues, letting doctors provide more precise neuromodulation.
“The next-generation neurostimulators will be more selective with fewer off-target effects,” Prof Feng said. “They should also be more intelligent by incorporating chemical and electrical sensory capabilities and ability to communicate bidirectionally to a cloud-based server.”
Prof Feng hopes that more people will be eventually able to achieve chronic pain relief with this technology. He is now working toward conducting clinical studies with his collaborators at UConn Health to test the efficacy of this method in humans.
Source: University of Connecticut
