Gut Feelings

Illustration by Kamila Giermakowski Rios

By Trixie Manaloto

The mosquito lands silently, drawn by the warmth of human skin that bled.
Her wings relax as she drinks and drinks until her belly glows red.
Until a moment when receptors in her rectum whisper to her brain: “enough.”
For days thereafter: No buzz. No bite. Her stomach, overstuffed.
She rests, content, as eggs begin to be produced in her brood.
What stilled her thirst for blood, and rewired her every mood? 

A mosquito’s brain doesn’t always decide when to bite you – sometimes, its rectum does.

Neuroscientist Chloe Greppi’s research sought to uncover what exactly creates this sense of satiation or “fullness” in mosquitos. Her team found that, deep in the insect’s hindgut, a special receptor called NPYLR7 activates when nutrients from human blood enter the gut (Greppi et al., 2025). This receptor consequently sends a signal to the brain, acting like a neuron, that switches off the mosquito’s craving for human scent.

Essentially, the gut “thinks”, creates a sensation, and controls her behavior.

And in humans, our guts are just as talkative. In fact, receptors from the same Neuropeptide Y (NPY) family are found in high concentration in the human brain and gut, which modulate the circadian rhythm and stimulate hunger (Pharmacology, 2017). In fact, Columbia University’s very own Dr. Michael Gershon was the first to call the gut our “second brain” (Gershon, 1999). Hidden in the walls of our intestines is a vast network of over 100 million neurons–more than the spinal cord itself. This structure, known as the enteric nervous system (ENS), can operate even if communication with the brain or spinal cord is severed. Studies have shown that peristalsis (the rhythmic contraction that moves food through the body) continues even when the gut is cut off from the brain or spinal cord. Unlike other organs that rely on constant direction from the brain, the gut can sense, decide and respond on its own, guided by its dense web of neurons. This interdependence allows it to regulate digestion automatically, ensuring food keeps moving even without signals from the central nervous system. 

This independence of the gut’s functions reveals how the gut actively negotiates with the brain, which makes it unlike any other organ that passively obeys the brain’s commands. Like Greppi’s work that showed gut signals sent to the brain in mosquitos (Greppi et al., 2025), Gershon’s decades of research show that the human ENS can even send more signals to the brain than the brain sends to the gut, making it one of the body’s most active communication highways (Gershon, 1999). 

Evolution, it seems, gave vertebrates two cooperating brains: one in the head and one in the bowel. The gut is an active participant in feeling; it senses distress, interprets emotion, and translates it into motion or a physical sensation. The flutter of “butterflies” before a presentation, the sinking stomach during grief, or the tightness during fear are all messages pulsing through its neurons. When the gut and brain have trouble sending messages to each other, there is, as Gershon writes, “chaos in the gut and misery in the head” (Gershon, 1999). Disorders such as irritable bowel syndrome, anxiety, and depression often emerge when this delicate connection is disrupted.

The same chemicals that shape our joy and sadness are also responsible for how smoothly a meal passes through us. Gershon’s research also revealed that the gut produces about 95% of the body’s serotonin, the neurotransmitter responsible for regulating mood, sleep, and appetite (Gershon, 1999). A surge of serotonin can quicken both the bowels and the mind; a deficiency can slow them down. The same molecule that steadies emotion also controls the speed of digestion. This overlap also explains why antidepressant medications (designed to raise serotonin levels in the brain) so often cause nausea or digestive distress. 

In this light, “gut feelings” become more than a nonsensical intuition. Gut feelings are the nervous system’s attempt to translate inner emotion into tangible physiology. When we say we have a bad feeling about something, it is not just language. It is neurons firing in our intestines, sending a message up to urgently warn the brain.

So, when emotion churns your stomach or calm settles it, it’s not “all in your head.”

It’s in your second brain; the one that works quietly beneath your ribs, creating a physical manifestation to convey your body’s instinctual messages.


References


Gershon, M. D. (1999). The second brain. Harpercollins World ; London.

Greppi, C., Frank, K., Saltz, V., & Duvall, L. B. (2025). A Signaling Hub in the Mosquito Rectum Coordinates Reproductive Investment After Blood Feeding. BioRxiv (Cold Spring Harbor Laboratory). https://doi.org/10.1101/2025.08.25.672111

​Pharmacology. (2017). Tocris Bioscience. https://www.tocris.com/pharmacology/npy-receptors#background