How the fresh touch travels from skin to brain

Key questions answered

Q: What did the researchers discover about how we feel cold temperatures?
A: The study identified a complete neural route from the skin to the brain dedicated to detecting cold temperatures, showing how this sensation is transmitted and amplified in the spinal cord.

Q: Why is this discovery important?
A: It is the first time that a complete temperature detection circuit is mapped, offering information about basic biology and opening the door to specific treatments for cold -induced pain, such as experienced by patients with chemotherapy.

Q: How does this route of cold pain signals differ?
A: The newly discovered circuit specifically feels harmless coldness and not medium with painful cold, which probably involves different and more complex roads.

Summary: An innovative study has mapped the complete neuronal circuit that transports cold temperature signals from the skin to the brain. The road begins with molecular sensors in the skin, which activate the neurons that send signals to the spinal cord, where the message is amplified before reaching the brain.

This precise circuit explains how we experience harmless freshness, such as entering a room with air conditioning, and is different from the roads involved in painful cold sensations. Understanding this route could lead to new treatments that relieve the discomfort related to cold without interrupting the normal perception of temperature.

Key facts:

Dedicated route: The researchers identified a complete neuronal circuit for cold temperature detection. Signal amplifier: an “amplifier” of the spinal cord increases the cold signal on the road to the brain. Medical relevance: the results can help the therapies objective for the pain induced by the cold without harming the normal sensation.

Source: Michigan University

The researchers at the University of Michigan have illuminated a complete sensory path that shows how the skin communicates the surrounding temperature to the brain.

This discovery, which is believed to be the first of its kind, reveals that cold temperatures obtain their own path, indicating that evolution has created different circuits for hot and cold temperatures.

This creates an elegant solution to guarantee precise thermal perception and the appropriate behavioral responses to environmental changes, said Bo Duan, lead author of the new study.

“The skin is the largest organ in the body. It helps us detect our environment and separate, distinguish different stimuli,” said Duan, an associate professor of UM of molecular biology, cellular and development.

“There are still many interesting questions about how this does, but now we have a way of how it detects cold temperatures. This is the first neuronal circuit for the temperature sensation in which the full path has been clearly identified from the skin to the brain.”

This work deepens our understanding of fundamental biology and brings us closer to an explanation of how we evolve to inhabit safe temperatures and avoid dangerous extremes, Duan said. But it also has medical implications that can be explored to help improve people’s quality of life in the future.

For example, more than 70% of people who have undergone chemotherapy experience pain caused by cold temperatures, Duan said. The new study found that the neuronal circuit responsible for detecting the harmless cold not this type of cold pain.

But, understanding how cold detection circuits works when it works correctly in normal conditions, researchers now have a better opportunity to discover what goes wrong in illness or injuries. It could also help develop directed therapies that restore a healthy sensation without affecting the normal perception of temperature.

This research was funded by the National Health Institutes and was carried out in collaboration with Shawn Xu and their research team at the UM Life Sciences Institute.

A great amplifier discovery

In his study, published in the journal Nature Communications, Duan and his team used sophisticated techniques of images and electrophysiology to observe how the mice transmitted the sensation of cold temperatures from their skin to the brain.

It is an approach that the team has applied to other sensations in the past. Directed by postdoctoral research partner Hankkyu Lee and doctoral students Chia Chun Hor and Lorraine Horwitz, the team focused on temperature on this work.

“These tools have allowed us to identify the neuronal pathways for chemical itching and mechanical itching previously,” Duan said. “Working together, the team identified this very interesting and very dedicated path for a great sensation.”

The cold signal begins in the skin, which houses molecules sensors that can detect a specific temperature range between approximately 15 and 25 degrees Celsius, equivalent to 59 and 77 degrees Fahrenheit. When those sensors get involved, they excite primary sensory neurons, which send the cold signal to the spinal cord. Here, the team discovered that the signal is amplified by specialized interneurons, which then activate the projection neurons that connect to the brain.

The researchers had previously known about the molecular thermometers of the skin, in part, the Nobel Prize in Physiology or Medicine 2021 obtained in California, but the spinal cord amplifier was an unknown key ingredient. With the disabled amplifier, the cold signal is lost in the noise, the team found.

Although the study was conducted in mice, it has been shown that each component of the circuit is in humans through genetic sequencing, Duan said. Therefore, we are likely to have the same path as to thank for the refreshing feeling of entering a room with air conditioning on a hot summer day.

In the future, the team is looking to identify the road or the roads involved in acute cold pain.

“I think the painful sensations will be more complicated,” said Duan. “When we are in more risky situations, there could be multiple ways involved.”

His team is also interested in how the brain processes these various skin signals and how we have evolved not only to differentiate between them, but also connect emotions with them to help us protect ourselves. In fact, it is the curiosity about such questions that originally motivated Duan’s work, which is perpetually remembered to work in Michigan.

“In summer, I love walking through Lake Michigan and having a soft breeze hit my face. I feel very good, very comfortable,” Duan said. “But winter is really terrible to me.”

About this perception of temperature and neuroscience research news

Author: Matt Davenport
Source: Michigan University
Contact: Matt Davenport – University of Michigan
Image: The image is accredited to Neuroscience News

Original research: open access.
“A dedicated circuit from skin to brain for cold sensation in mice” by Bo duan et al. Nature communications

Abstract

A Dedicated Circuit from brain for a cold sensation in mice

The perception of external temperature is essential to maintain homeostasis and avoid thermal lesions. Although molecular thermosensors have been identified, such as the transitional receiver potential, type 8 melastatin (TRPM8), the neuronal circuits responsible for transmitting cold signals are still not clear.

Here we show that a spinal circuit in mice transmits cold signs of the skin to the brain. The exciting interneurons in the spinal dorsal horn that expresses the thyrotropin liberating hormones (TRHr+) act as a central cube for cold sensation.

These TRHR+ neurons receive monosineptic information from TRPM8+ sensory afferents and are selectively activated by cold cold stimuli. The ablation of the interneurons trhr+ abole the behavior responses to the cold, but not to the hot or cold stimuli.

We also identify a population of positive spinal projection neurons for the calcitonin receiver (Calcrl+) that receive convergent contributions from both the TRPM8+afferents and the interneurons THR+, and transmit specific cold signals to the lateral winding nucleus (LPBN).

Our findings define an advance amplification circuit for cold sensation and reveal a specific spinal route of modality for thermal processing.