Female mice like warmer spaces than males because of two types of tiny temperature sensors in their nerves which are tuned to switch on at higher temperatures, according to researchers at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King's College London.
The study, led by researchers at the Wolfson Sensory, Pain and Regeneration Centre at IoPPN and published today in The Journal of Physiology, explains at a molecular level a sex difference seen in every mammal studied so far, and even in birds.
An animal's preferred external temperature can vary between individuals, but there are general trends. Female mice will choose a floor temperature of 36°C, compared to the male preference of 32°C. These trends are also seen in humans. On average, women prefer a room at around 25°C and men around 22°C. The new study points to two ion channels behind it - tiny pores in nerve cells that open as the temperature changes, letting charged particles flood in and ultimately fire a signal to the brain. TRPM2 picks up gentle warmth; TRPM8 picks up coolness. In female mice, both types of channel activate at warmer temperatures than in males. So, a floor that feels pleasantly warm to a female feels unpleasant to a male. While the study was done in mice, humans also have both types of ion channel.
It has long been known that in many mammals, including humans, females prefer a warmer environment than males, but the molecular basis for this difference had not been identified until now.
Professor Peter McNaughton, Professor in Pharmacology at the Wolfson Sensory, Pain and Regeneration Centre, IoPPN
Professor McNaughton, the senior author on the study, added:
"In mice, we found that the thermal ranges of activation of the two ion channels that detect warmth and coolness, TRPM2 and TRPM8, are shifted towards warmer temperatures in females, and it is this shift that causes the difference in how males and females sense and react to temperature. This study did not look at humans, but humans have both of these types of ion channels, and similar differences in average temperature preference so it is likely that a similar mechanism is at work."
The researchers placed mice on two heated metal plates, that could be gently warmed, side by side. One was kept at 33°C and the other was varied, and the team watched which one the mice chose to stand on. Males avoided a plate heated to 38°C, while females strongly preferred it. Genetically removing the warmth sensor shifted males towards preferring warmer temperatures. Removing or blocking the cool sensor shifted females towards cooler ones. Because a genetic change and a drug that blocked the sensors gave the same result, the researchers conclude that the effect was due to direct actions on the sensors themselves.
Hormones play a part in this process. Lowering testosterone in male mice shifted them towards the female preference for warmth, and raising it in females made them more averse to warmth. Female sex hormones had no effect, and testosterone didn't explain the whole difference. Body temperature wasn't the cause either. Males and females had the same core and skin temperature, which suggests the mice were responding to what they felt through their paws.
Dr Bruno Vilar, from the Wolfson Sensory, Pain and Regeneration Centre, IoPPN, said:
"Much of the earlier work on temperature sensing, including our own, was carried out only in male mice. However, genetically removing the warmth sensor TRPM2, whichhad a large effect on how males responded to warmth, had almost no effect in females. We wanted to understand why, and that led us to discover that both sensors are shifted towards warmer temperatures in females."
Some questions remain. The sensors were genetically removed throughout the body, so the team can't yet say for sure whether the difference lies in the nerves that detect temperature or in how the brain reads their signals. Nerve cells isolated in the lab also didn't show the pattern seen in the animals, which the researchers put down to the effects of the isolating these neurons on their biological processes. Next, they hope to genetically fine-tune the two sensors at the nerve ending in the paws and test whether that changes how the animals behave.
TRPM8 and TRPM2 ion channels determine sex differences in thermal preference in mice (Vilar et al. 2026), is published in The Journal of Physiology. DOI: 10.1113/JP288076.
This research was funded by the Wellcome Trust.
