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Scratch That Itch: Brain Mechanism Identified
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Scratch That Itch: Brain Mechanism Identified

Written by Dr. Lakshmi Venkataraman, MD
Article Reviewed by 
The Medindia Medical Review Team on December 17, 2018 at 4:04 PM
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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.

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Scratch That Itch: Brain Mechanism Identified

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

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.

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.

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 :
  1. 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

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