A team of researchers from the Indian Institute of Science (IISc), Bengaluru, and Kolkata-based institute TCG-CREST have identified the “brain circuit” that involves the sensations associated with a certain side effect of chemotherapy known as “cold allodynia”. The discovery was published in the reputed journal Cell Reports in a research paper titled, “Parabrachial inputs to the parafascicular thalamus drive sensory and affective-motivational responses to cold-allodynia in mice”.

We explain what cold allodynia is, how scientists narrowed down its cause, and what the findings mean for humans.

What is cold allodynia?

Cold allodynia is a condition in which the sufferer may feel pain or distress from even a regular level of cold temperatures. It is one of the side effects that are part of “chemotherapy-induced peripheral neuropathy”, which includes many chemotherapy-induced neural side effects such as temperature sensitivity, a feeling of pins and needles, or pain etc.

Story continues below this ad

Cold allodynia specifically is known to be one of the side effects of oxaliplatin, a commonly used chemotherapy drug that contains platinum.

How did the team narrow it down and verify it?

IISc’s Professor Arnab Barik, one of the study’s co-authors, told that cold allodynia is a very specific side effect wherein apart from damage to the nerve endings, there is a sensitivity to cold but not to heat. While it is most commonly a side effect of platinum-based chemotherapy drugs, it can also be down to viral infections, injuries, or diabetes. He also said that while the damage to nerve endings could heal, the cause could persist and result in chronic pain.

The cause of cold allodynia was tested using mice. “What we have found is that there is a ‘circuitry’ that changes after you expose the mice to chemotherapy. Even after you stop the chemotherapy and everything has healed, the pain stays. That is reflected in some changes in the brain that do not come back to normal easily,” Barik said.

Story continues below this ad

“We traced the neural circuits in the affected part and how they reach the brain. We found that the connection between the lateral parabrachial nucleus and parafascicular region of the thalamus — it specifically changes after chemotherapy,” he added.

The lateral parabrachial nucleus refers to a group of nerve cells in the upper brainstem that processes pain, taste, breathing, and body fluid signals, whereas the parafascicular region of the thalamus refers to a key group of nerve cells located within the brain’s thalamus that plays a critical role in both motor control and pain regulation.

Does this finding apply to humans?

In this case, the experimentation on laboratory mice was invasive in nature, and cannot be carried out on humans. Barik said: “In the long term, we are looking at how to fix the issue pharmacologically, and then test that in mice. That could be much easier to translate to humans.”

“We are trying to understand better whether this finding is specific to chemo pain or can be extended to other forms such as from injuries. We are testing those, and the idea is to try and reverse that — that is the plan for the next five years or so,” he added.