Why naked diggers are insensitive to pain

Naked diggers are superheroes in the animal world

marks, Geektimes

Under the dry plains of East Africa there are animals that surprise both with their appearance and their capabilities. We are talking about naked diggers. Their body is not covered with fur, they have very poor eyesight but good sense of smell, touch and strong paws. These animals can dig long passages in the ground with a length of several kilometers.

They live in colonies of up to 300 inhabitants. The queen is the main one in the colony. This is the only female that reproduces offspring. Rodents that have been born grow up quickly. All my life (about 30 years) these animals spend in conditions of a small amount of food and water. Naked diggers are small animals with a body length of 8-10 cm, a tail of 3-4 cm and a weight of 30-35 g. Females are larger: they weigh from 50 to 80 g.

The naked digger lives in dry savannas and semi-deserts of Kenya, Ethiopia and Somalia. They are secretive burrowing animals that feed on underground parts of plants, including succulent tubers and bulbs. Food is stored in specially equipped underground storerooms. Naked diggers do not drink water at all and feed almost exclusively on plant tubers. They get moisture together with food.

Apparently, in order to somehow offset the hardships of life of naked diggers, nature has rewarded them with unique opportunities. For example, they have almost no cancer. They live much longer than other rodents – 30 years or more. In addition, these animals are insensitive to acid burns and do not feel pain during temperature burns. And even without burns, the rodent does not feel pain when exposed to high temperature. In addition, the diggers are distinguished by their endurance to high concentrations of CO2. Interestingly, despite the almost complete absence of an external auditory shell, the hearing of animals is acute, as evidenced by the extensive repertoire of sounds made by diggers.

Scientists have been studying naked diggers for a long time, trying to understand what causes their unique features. Recently, an article appeared in the authoritative publication Cell Reports explaining the insensitivity of naked diggers to pain (Omerbašić et al., Hypofunctional TrkA Accounts for the Absence of Pain Sensitivity in the African Naked Mole-Rat). As it turned out, evolutionary changes led to the modification of amino acids in their pain receptors. In addition, experts note the almost complete absence of a "pain neurotransmitter" in adults.

Figure from an article in Cell Reports – VM

Scientists suggest that naked diggers are unlikely to have received their unique capabilities if they did not live in extreme conditions, including social characteristics. Experts know of only two species of animals whose lifestyle is so similar to that of social insects – these are naked diggers and their close relatives, the blind.

Females in the colony fight to the death for the right to be queen, after which they occupy this social position up to 15 years in a row. Having changed the social status, the animal increases in size, not only due to weight gain, but also due to an increase in the distance between the vertebrae. After the death of the queen, a deadly fight begins between the fertile females of the colony, and after the final victory, the winning female becomes the head. Successful colonies can be very large, with an extensive system of moves. Naked diggers dig the ground with their paws and teeth. Despite the fact that the nest chambers are quite large, there can be a lot of inhabitants crammed in there, which probably causes them some inconvenience.

Diggers, like other animals, have a tendency to thermal hyperalgesia. This phenomenon is also characteristic of humans. It is not so difficult to explain the nature of thermal hyperalgesia. Imagine, for example, a severely sunburned skin on your back. What will you feel if you direct warm water to this area? Not hot, but really warm, as we feel the temperature of the water in the usual state. But for the burned area, this water will seem extremely hot.

The thing is that the temperature sensors located on the damaged area are chemically "overstimulated" as a result of the action of fire, sunlight or any other energy source. Therefore, even a gentle touch to the burn is perceived by sensors as a painful sensation. The pain signal is sent to the brain, and the living being feels pain. Everything is logical.

In the case of naked diggers, the situation is a little different. When an animal digs in dry soil, the sensors located in the skin become overexcited. But at this time, the rodent does not feel pain, as it happens, for example, with a person. And all thanks to special changes in the structure of amino acids of the skin sensors of the animal. These changes have led to the fact that the naked digger does not feel pain when exposed to high temperature. After the injection of a neurotransmitter known as "substance P", the pain in the diggers is fully manifested.

"We believe that evolutionary changes have led to the fact that the pain sensitivity of rodents has not disappeared completely, since it represents an undoubted benefit for the animal. But nature has weakened the pain of the diggers to such an extent that they do not cause any particular inconvenience to the rodent. Naked diggers live underground in desert regions, they don't get much food. The level of metabolism of diggers is significantly lower than the level of metabolism of any of the mammals. Under these conditions, evolution has removed what is not absolutely necessary," says Gary Levin, lead author of the study, in a press release from the Max Delbrück Center for Molecular Medicine in the Helmholtz Association How the naked mole-rat escapes inflammatory pain.

Levin and his colleagues also found that diggers are born with normal skin sensitivity to heat. But, growing up, they lose this ability. This helps them save more energy, which is needed in the conditions under which diggers exist. What is interesting is that small changes in the structure of the amino acids of the rodent organism led to significant consequences.

Now rodents live without constant discomfort, which, undoubtedly, they would experience if they had a normal sensitivity to high temperature. And this is correct, because pain is not always necessary for a living organism. In some cases, it only gets in the way. In the case of naked diggers, pain would be an obstacle to the survival of the entire species. And the evolutionary process has led to the disappearance of the animal's susceptibility to "heat pain" as such.

Portal "Eternal youth" http://vechnayamolodost.ru  17.10.2016