Scratch That Itch: Brain Mechanism Identified

Highlights:

A small subset of neurons in the periaqueductal gray matter, an area in the deeper portion of the brain may be involved in the vicious loop of itching (or pruritis) sensation and scratching
The activity of the periaqueductal gray matter that produce a neurotransmitter called glutamate and a neuropeptide called tachykinin 1 (Tac1) was tracked
Destroying the tachykinin 1 (Tac1) producing neurons significantly decreased itch-induced scratching
Findings of the current study may give rise to new treatment targets with the scope to develop newer and more effective drugs to manage chronic itching

A small set of neurons present in the periaqueductal gray area of the brain may be involved in the production of itching and the itch scratch feedback loop (itching sensation leads to scratching and scratching causes more itching), according to a recent study conducted by the Chinese Academy of Sciences.

This finding may have possible implications in the identification of newer treatment targets and development of better drugs to treat chronic itching conditions. The findings of the study appear in the journal Neuron.

Itchy Skin | Pruritus – Causes, Symptoms, Diagnosis, Treatment
Itchy skin is an unpleasant skin sensation that urges the person to scratch. The main causes of itchy skin include dandruff, allergic reactions.

‘Identifying the brain area involved in processing and production of chronic itch may give rise to new treatment targets and development of newer and more effective therapies for chronic itching’
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Driving Force Behind Current Study

Previous research has outlined possible neurons in the spinal cord that may be involved in the production of itching such as cells that express the gastrin-releasing peptide receptor (GRPR)
However, the brain areas involved in itch processing and production remain unclear
Scientists involved in the current study postulated that the periaqueductal gray area of the brain may play a role since it is known to play a key role in the processing and production of sensory stimuli such as pain

The current study was undertaken to confirm the above hypothesis

Test Your Knowledge on Itching / Pruritus
Itching, also called pruritus, is a sensory experience that causes an impulse or reflex to scratch at the point of itch. While the mechanism of how to stop itching is unknown, it is believed that pain inhibits itch. Causes of itching include infections, allergies, bug bites, chronic diseases, dry skin or sun exposure.

Testing the Role of Periaqueductal Gray Neurons in Itch Production

The current study was carried out in mice and the study team firstly induced itching sensation and scratching in mice by either injecting a chemical called histamine or chloroquine an antimalarial drug
The team then tracked the activity of a specific subset of neurons in the mice periaqueductal gray matter that produce a neurotransmitter called glutamate and a neuropeptide called tachykinin 1 (Tac1)
Destroying the tachykinin 1 (Tac1) producing neurons significantly decreased itch-induced scratching
On the other hand, stimulating the tachykinin 1 (Tac1) producing neurons caused spontaneous itching sensation and scratching even in the absence of histamine and chloroquine by activating the GRPR-expressing neurons in the spinal cord

The findings of the study, therefore, suggest that the tachykinin 1 (Tac1) producing neurons of the periaqueductal gray matter in the brain may play a role in itch production.

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Role of Itching and Its Trigger Factors

The itching sensation can be triggered by several factors such as insect bite, skin allergic reaction pregnancy, drugs, cancer treatment, skin diseases and fungal or parasitic infections.

Itching and scratching play a protective role in the removal of certain irritants or insects that may have attached to the skin
Sometimes itching may elicit an immune reaction which helps to overcome the offending agent

Nevertheless, the itching and scratching feedback loop may sometimes be persistent resulting in skin injury and damage that may be disfiguring as well as affecting the quality of life.

Mild itching can be treated by antihistamine (antiallergic) tablets, steroid creams and gels or moisturizing lotions to reduce inflammation. However, these treatments may not be very effective in severe and chronic itchy conditions.

Home Remedies for Itchy Skin
Natural home remedies can offer you an herbal method to treat itchy skin effectively. Follow these simple home remedies and tips to get rid of itchy skin.

Future Research Plans

Study team plans to investigate whether the Tac1 producing neurons can be targeted by drugs as possible treatment of chronic itching conditions
They also plan to look for other neurons that may have a possible role in itch production

Conclusion

In conclusion, the study findings may pave the way for further research into the development of newer and more effective treatments of chronic itching, which can not only impact the quality of a person’s life but be cosmetically disfiguring as well.

Reference:

Tac1-Expressing Neurons in the Periaqueductal Gray Facilitate the Itch-Scratching Cycle via Descending Regulation - (http://dx.doi.org/10.1016/j.neuron.2018.11.010)

Source-Medindia