How is Your Brain Able to Sense an Itch?
In a recently published study, researchers at the Salk Institute have unraveled how neurons in the spinal cord facilitate the transmission of itch signals to the brain.
The ability to sense light touch is critical. It is central to many tasks that we perform daily and vital for ensuring our safety. The sensation helps to keep us vigilant of things that might harm us, including biting insects that may cause not only itching but other health issues as well.
Cell Reports recently published findings that shed light on how the brain is able to sense an itch, such as that caused by biting insects. These findings documented how certain neurons in the spinal cord assist in the transmission of signals to the organ.
“The takeaway is that this mechanical itch sensation is distinct from other forms of touch and it has this specialized pathway within the spinal cord,” said senior author Professor Martyn Goulding.
This new research adds to the existing knowledge of itch. Furthermore, it may help in the development of treatments for chronic itch. Such chronic itch can be overwhelming to patients especially in conditions such as eczema, psoriasis, and diabetes.
The Role of Inhibitory Neurons
In previous research, Goulding and his team had uncovered certain inhibitory neurons in the spinal cord that turn off a mechanical pathway most times to prevent itching. These neurons produce a neurotransmitter known as neuropeptide Y (NPY) and essentially function like cellular brakes.
In the absence of these neurons, the mechanical itch pathway would constantly be on “on” state. Thus resulting in a chronic itch. However, what was not clear were the exact mechanisms by which the brain is able to pick itch signals.
Postdoctoral fellow David Acton formed a hypothesis that in the absence of NPY inhibitory neurons, those neurons typically responsible for transmitting light touch signals start acting like an accelerator, trapped in the “on” position.
The researchers identified a candidate for the “light touch” neurons, which are excitatory spinal cord neurons expressing the receptor for NPY – known as Y1 spinal neurons.
Fighting Chronic Itch
An experiment involving removal of the NPY and Y1 neurons was carried out by Salk researchers.
The results demonstrated that in the absence of Y1 “accelerator” neurons, scratching was absent in mice. Moreover, even following administration of a stimulus that would typically cause them to scratch, such was absent.
When the lab animals were given drugs activating the Y1 neurons, the researchers noticed that they scratched impulsively, even when not exposed to any touch stimuli.
Going further, Goulding and his team were able to demonstrate how the NPY regulates the excitability of Y1 neurons. The neurotransmitter helped to control sensitivity to light touch.
These findings may prove very interesting for people with psoriasis. Other researchers have observed that such individuals typically have NPY levels that are lower than average. This new study suggests that the lower levels may be the cause of itching that sufferers usually experience.
The scientists expressed the need for further research to map out the complete mechanical itch pathway. This will potentially help for developing drugs that can reduce the itch sensation and combat chronic itching.