The need to gnaw in mice and hamsters is related not only to tooth growth but also to the functioning of certain nerve circuits in the brain. This conclusion was reached by researchers whose work was published in the journal Neuron.
These animals have continuously growing incisors. To prevent them from becoming too long and interfering with food intake, rodents need to regularly wear them down. However, scientists noticed an unusual phenomenon: some laboratory mice had excessively long teeth, even though their diet was no different from that of other individuals. This led specialists to suspect that the cause might be related not to nutrition, but to the characteristics of the nervous system.
To test the hypothesis, researchers used genetically modified mice. Their nerve cells were made sensitive to a specific toxin. After the substance was introduced, these neurons were destroyed, allowing the observation of how the animals' behavior changed.
It turned out that there are touch-sensitive neurons in the teeth that are connected to two circuits. One of them is responsible for the proper closing and movement of the jaws, while the other is linked to the area of the brain that produces dopamine. This area is involved in the formation of the reward sensation.
Signals generated during chewing are transmitted from the teeth to the brain and, apparently, activate the dopamine system. When these connections were disrupted, the mice stopped gnawing on objects, and their incisors began to uncontrollably elongate.
The authors of the study believe that the mechanisms discovered may not be characteristic only of rodents. They suggest that similar neural circuits regulating oral behavior may be present in many species of animals.
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