Mapping the Reflex Mechanisms May Alleviate Chronic Pain

Reflexes are immediate and involuntary actions to a particular stimulus. They make up our day-to-day activities such as "sudden jerky withdrawal of hands on touching a hot kettle", catching yourself automatically when you miss a rung on a ladder. These motions don't require forethought and are almost instantaneous. The physical organization of cells in the spinal cord that help mediate these and similar critical "sensorimotor reflexes" are sketched out as per researchers at the Salk Institute, published in the journal Neuron.

The reflex movements are relayed from sensory neurons that detect touch, heat, and painful stimuli to motor neurons, which cause the muscles to take action. In-between, these actions are relayed upon by the interneurons in the spinal cord, which serve as sort of "middlemen," thereby saving time by bypassing the brain.

‘Mapping of the reflex mechanisms mediated by different layers of interneurons reveals their physical organization. This aids in exploring the pathological changes in the somatosensory system that result in chronic itch or pain and design better management strategies for chronic pain.’

"There's been a lot of research done at the periphery of this system, looking at how cells in the skin and muscles generate signals, but we didn't know how that sensory information is trafficked and interpreted once it reaches the spinal cord. This new work gives us a fundamental understanding of the architecture of our sensorimotor system", says Martyn Goulding, a professor in Salk's Molecular Neurobiology Laboratory and holder of the Frederick W. and Joanna J. Mitchell Chair.

The Reflex Pathway:

Using molecular engineering tools earlier developed by the team, they demonstrated the organization of these spinal reflexes in mice. Mapping of the particular interneurons that were active during reflex sensations like itch, pain, or touch was done initially, followed by probing the function of concerned interneurons. The functions were assessed by turning them on and off individually and observing how the resulting reflex behaviors were affected.

It was found that the interneurons in the outermost layer of the spinal cord were involved in relaying reflexive messages related to itching between sensory and motor cells. Deeper interneurons mediated messages of pain-causing a mouse to move a foot touched by a pin, for instance. And the deepest set of interneurons helped mice reflexively keep their balance, stabilizing their body to prevent falling.

Neurons in each spatial area that had different molecular signatures revealed the same function, while the more similar neurons located in different areas of the spinal cord were responsible for different reflexes.

Thus, the study proved the physical architecture of the interneuron circuits that make up these different reflex pathways. However researchers are set to explore the interactions among these interneurons and further investigate the pathological changes in the somatosensory system that result in chronic itch or pain. This would help design better management strategies for chronic pain.

Source: Medindia