Food cravings are a familiar—and sometimes surprising—part of pregnancy. Someone who rarely eats sweets may suddenly crave ice cream, while another person may develop a strong desire for salty or high-fat foods. Although pregnancy cravings are well known, scientists are still working to understand what causes them. New research offers an intriguing clue: a study in mice identified a specific brain circuit involving serotonin, a chemical messenger involved in mood, appetite and reward. The researchers found that pregnancy alters the activity of certain serotonin-producing neurons, potentially making highly rewarding foods more appealing. Although the research was conducted in mice, it may help explain why food cravings can become particularly strong during pregnancy.
What Is Serotonin?
Serotonin is a neurotransmitter, a chemical in the body that helps nerve cells communicate with one another. It is involved in numerous processes throughout the body and brain, including mood, sleep, appetite, digestion and aspects of learning and reward. Because serotonin influences appetite and food-related behavior, researchers have long been interested in how changes in serotonin signaling might affect eating.
However, serotonin is not simply an “appetite chemical,” and its relationship with eating behavior is complicated. Different serotonin pathways can have different effects depending on which brain regions and receptors are involved. The new pregnancy study illustrates just how specific those effects can be by identifying a particular group of serotonin-producing neurons that may help regulate the motivation to seek highly rewarding foods.
Researchers Identify a Serotonin Circuit Linked to Food Cravings
The study focused on serotonin-producing neurons in an area of the brain called the dorsal raphe nucleus (DRN). The DRN is one of the brain’s major sources of serotonin. Researchers found that pregnancy changed the electrical activity of a particular population of serotonin neurons in this region. Specifically, these neurons became less active during pregnancy, and the researchers linked this change to increased motivation for highly palatable foods; foods that are especially rewarding because of their taste and other sensory characteristics, such as foods high in sugar or fat.
The researchers then investigated why these serotonin neurons became less active. That’s where a molecule called SK3 entered the picture. SK3 is a type of potassium channel found on neurons, and potassium channels help regulate the electrical activity of nerve cells. In this study, pregnancy increased SK3 activity in the serotonin neurons being investigated, making them less excitable and less likely to fire. A useful way to think about SK3 is as a kind of brake on neuronal activity: during pregnancy, that brake appeared to become stronger in these particular serotonin neurons.
Importantly, the researchers did more than simply observe this change. They conducted experiments to determine whether SK3 was actually contributing to the behavior. When they removed SK3 from the relevant serotonin neurons, the pregnancy-associated decrease in neuronal activity was reduced, and the animals showed less of the craving-like behavior observed during pregnancy. Conversely, increasing SK3 activity in nonpregnant mice produced changes resembling those seen during pregnancy. These experiments suggest that SK3 may be an important part of the mechanism rather than simply being associated with it.
How Does Serotonin Affect the Brain’s Reward System?
The researchers also traced the connections made by these serotonin neurons and found that they communicate with a region called the ventral tegmental area (VTA). The VTA is an important part of the brain’s reward and motivation system. It is closely associated with dopamine signaling and helps regulate how strongly we are motivated to pursue rewarding experiences, including food.
The study suggests that serotonin neurons in the DRN normally help regulate activity in this reward-related region. During pregnancy, reduced activity in the specific serotonin neurons studied may decrease their influence over the VTA. As a result, the reward system may respond more strongly to highly palatable foods. In simplified terms, the proposed sequence is: pregnancy increases SK3 activity, SK3 reduces the firing of certain serotonin neurons, and this changes how those neurons regulate reward circuitry, potentially increasing motivation for highly rewarding foods.
The researchers found additional evidence for this connection by manipulating the pathway directly. Artificially activating the DRN-to-VTA pathway in pregnant mice reduced food-seeking behavior, while silencing the pathway in nonpregnant mice increased craving-like behavior. Together, the findings suggest that this specific serotonin pathway plays a role in regulating food motivation during pregnancy.
How Pregnancy Changes Serotonin Signaling
The study does not suggest that pregnancy simply lowers serotonin throughout the brain. Instead, researchers found that pregnancy changes the activity of a specific group of serotonin-producing neurons and the brain circuit they connect to. In particular, pregnancy increased the activity of a potassium channel called SK3, which made these serotonin neurons less active. This change in serotonin signaling may alter communication with the brain’s reward system and contribute to the increased motivation for highly palatable foods observed in pregnant mice.
This distinction is important when discussing serotonin and pregnancy. Serotonin levels and serotonin signaling are not necessarily the same thing. A change in how frequently specific serotonin neurons fire can affect behavior without causing a generalized decrease in serotonin throughout the brain. The findings therefore point to a more targeted change in serotonin signaling rather than a simple serotonin deficiency.
Pregnancy, Hormones and Food Motivation
The researchers believe that the observed changes may be part of the body’s adaptation to pregnancy. Pregnancy dramatically changes physiology, including hormones, metabolism, energy requirements and numerous processes in the brain. Food intake is particularly important during this period, so it makes biological sense that pregnancy could influence brain systems involved in appetite, motivation and reward.
The study raises the possibility that changes in serotonin circuitry help modify the motivational value of certain foods during pregnancy. However, researchers do not yet know exactly how pregnancy triggers the changes in SK3 activity. One important question for future research is whether pregnancy hormones, including estrogen and progesterone, influence SK3 activity in these serotonin neurons. Understanding this potential connection could help scientists trace the pathway from hormonal changes during pregnancy to changes in appetite and food-related behavior.
What Does This Mean for Pregnancy Cravings in Humans?
It is important to note that this research was conducted in mice, not pregnant humans. Animal studies are valuable because researchers can manipulate individual neurons and molecular pathways in ways that cannot be done in people. However, findings in mice do not automatically mean that exactly the same mechanism occurs in humans. Researchers will need to determine whether the SK3-related pathway exists and functions similarly in human pregnancy.
Human food cravings are also influenced by many factors, including hormones, metabolism, emotions, memories, sensory preferences, sleep, stress and the availability of particular foods. The serotonin circuit identified in this study may be one piece of the puzzle rather than a complete explanation for pregnancy cravings. It also does not explain why one person might crave sweets while another develops a preference for salty or savory foods.
Potential Implications for Future Research
The findings could eventually help scientists better understand conditions involving appetite, reward and eating behavior, but any potential medical applications are still a long way off. SK3 and serotonin are involved in important neurological processes, so altering these systems could have effects beyond food cravings. The study should not be interpreted as evidence that serotonin or SK3 should be manipulated during pregnancy.
For now, the value of the research is primarily scientific. By identifying a specific potassium channel, a population of serotonin neurons and a connection to the brain’s reward circuitry, the researchers have provided several concrete targets for future investigation. Further studies will be needed to determine whether the same mechanism occurs in humans and how pregnancy hormones influence it.
What the Research Reveals About Serotonin and Pregnancy
The relationship between serotonin and pregnancy is more complex than the idea that pregnancy simply lowers serotonin and causes food cravings. This new research in mice suggests that pregnancy can alter the activity of specific serotonin-producing neurons in the brain. A potassium channel called SK3 appears to act as an important regulator of those neurons. When SK3 activity increases, the serotonin neurons become less active, potentially changing their influence on the brain’s reward circuitry and increasing motivation for highly palatable foods.
The findings offer a fascinating potential explanation for why food cravings can change during pregnancy while also demonstrating how much more there is to learn about the brain’s response to pregnancy. For now, the results remain preliminary and cannot be assumed to apply directly to humans. Still, the study highlights an important point: pregnancy doesn’t just change the body—it can also produce highly specific changes in the brain. Understanding those changes may eventually help researchers explain some of the powerful shifts in appetite and food motivation that accompany pregnancy.
