Do kiwis and sauerkraut make your mouth water? If so, you can thank the mood-regulating neurotransmitter called serotonin, which may also enable you to taste sour foods, according to a study published last month in the Journal of Neuroscience and covered today by Science News.

When you eat a sour food, the acid in it triggers a response in the taste receptor cells found on your taste buds. The taste receptors release chemical compounds designed to lock into special nerve cells found on the tongue, which then relay messages to the brain.

Previous studies have suggested that eating sour foods causes the release of serotonin, a compound that can affect many basic bodily functions such as appetite, sleep, memory, mood, and sexual desire. We usually hear about serotonin’s role in the brain, since it’s often associated with feeling happy, but in fact the compound can be found in several parts of the body, including in the central nervous system, on the tongue. Maybe, the researchers thought, serotonin is relaying the sour message from the taste receptors to nerves on the tongue.

To test that, the researchers programmed a green-glowing protein to fit into any serotonin receptor on the nerve cells. They found the highest concentration of the fluorescing proteins on the part of the tongue known to detect sour tastes. And though other foods are known to trigger serotonin production in the brain, the researchers concluded that was the first definite evidence that serotonin is the neurotransmitter that tells the brain when a food is sour.

The researchers stumbled upon another strange finding as well: One of the anesthetics they used on their mouse subjects, called pentobarbital, blocked the receptors on nerve cells in the tongue from absorbing serotonin at all. That anesthetic is frequently used in taste studies, the researchers write, which might call previous findings into question.

Wonky serotonin levels have been linked with health conditions including insomnia and depression, but the relationship between those conditions and different types of foods or tastes is still poorly understood. Future studies may further explore the relationship between chemical compounds like serotonin and the sense of taste in humans.