Summary: Serotonin-producing neurons in the midbrain control both hunger-driven and pleasure-driven eating, but the circuits that govern each type of feeding are distinct and operate independently.
Source: Baylor College of Medicine
We often eat for reasons other than physical hunger—because food tastes good, because of social situations, or simply out of habit—even when we are already full.
Overeating, whether motivated by true energy need or by pleasure and environmental cues, contributes to obesity. According to the Centers for Disease Control and Prevention, roughly 42% of U.S. adults are affected. To better understand the brain mechanisms that drive different kinds of feeding and to inform possible treatments for overeating and obesity, an international research team led by scientists at Baylor College of Medicine studied how the brain regulates hunger-driven versus non-hunger-driven feeding in an animal model.
Under the leadership of Dr. Yong Xu, professor of pediatrics—nutrition and molecular and cellular biology at Baylor, the team found that serotonin-producing neurons in the midbrain influence both types of feeding but do so through two separate, independent neural circuits. The researchers also pinpointed two serotonin receptors and two ion channels linked to these circuits, suggesting new molecular targets for interventions that could reduce overeating. Their findings are published in the journal Molecular Psychiatry.
Distinct neural pathways govern hunger-driven and pleasure-driven eating
The investigators mapped two separate circuits formed by serotonin-producing neurons in the dorsal raphe region of the midbrain. One circuit projects to the hypothalamus—a brain area well known for regulating appetite and energy balance—while the other projects to a different midbrain region, the ventral tegmental area (VTA), which is involved in reward and motivation.
Activation of the pathway from dorsal raphe serotonin neurons to the hypothalamic arcuate nucleus predominantly suppresses hunger-driven feeding. In contrast, activation of the pathway from those serotonin neurons to the VTA primarily reduces feeding that is not driven by hunger, such as eating motivated by pleasure or environmental cues. In other words, the brain uses parallel but functionally separate circuits to control eating in response to internal energy needs versus external, reward-related triggers.
This circuit-level separation implies that interventions targeting one pathway could influence one type of feeding without necessarily affecting the other, opening the possibility of more precise approaches to curb overeating depending on its underlying cause.
Molecular targets: serotonin receptors and ion channels
Beyond mapping the circuits, the study identified receptor and ion channel mechanisms that mediate how these pathways influence feeding behavior. Two serotonin receptor subtypes—5-HT2C and 5-HT1B—were implicated in suppressing both hunger-driven and non-hunger-driven feeding. The data suggest that pharmacological strategies that engage both receptors could produce additive or synergistic effects to reduce food intake.
The researchers also found distinct roles for two ion channels in these circuits. A GABAA receptor (a chloride channel) is important for modulating the serotonin circuit that controls hunger-driven feeding but does not appear to affect non-hunger-driven eating. Conversely, a specific potassium channel influences the serotonin pathway that governs non-hunger-driven feeding but not the hunger-driven pathway. This clear functional segregation indicates that ion channel modulation could offer targeted ways to influence one type of feeding without disrupting the other.
Encouraged by these results, the team plans additional studies to identify molecules that can modulate these ion channels and to test whether modifying their activity can reduce overeating in animal models. They also intend to investigate how dietary and nutritional factors may alter ion channel function at the molecular level, potentially linking diet composition to circuit activity and feeding behavior.
About this neuroscience research news
Source: Baylor College of Medicine
Contact: Press Office – Baylor College of Medicine
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Original Research: Open access. “5-HT recruits distinct neurocircuits to inhibit hunger-driven and non-hunger-driven feeding” by Yanlin He, Xing Cai, Hailan Liu, Kristine M. Conde, Pingwen Xu, Yongxiang Li, Chunmei Wang, Meng Yu, Yang He, Hesong Liu, Chen Liang, Tingting Yang, Yongjie Yang, Kaifan Yu, Julia Wang, Rong Zheng, Feng Liu, Zheng Sun, Lora Heisler, Qi Wu, Qingchun Tong, Canjun Zhu, Gang Shu, Yong Xu. Molecular Psychiatry
Abstract
5-HT recruits distinct neurocircuits to inhibit hunger-driven and non-hunger-driven feeding
Obesity often results from consuming more calories than the body needs, but the neural drivers of excess eating are not fully understood. Serotonin (5-hydroxytryptamine, 5-HT) neurons in the dorsal raphe nucleus (5-HTDRN) influence diverse feeding behaviors, including eating to relieve hunger and eating for pleasure.
The study shows that activation of 5-HTDRN projections to the hypothalamic arcuate nucleus (5-HTDRN → ARH) suppresses hunger-driven food intake via actions at ARH 5-HT2C and 5-HT1B receptors. By contrast, activation of 5-HTDRN projections to the ventral tegmental area (5-HTDRN → VTA) suppresses non-hunger-driven feeding primarily via 5-HT2C receptors.
Mechanistically, hunger-driven feeding recruits ARH-projecting 5-HTDRN neurons by reducing their sensitivity to inhibitory GABAergic inputs, while non-hunger-driven feeding activates VTA-projecting 5-HTDRN neurons through a reduction in a potassium outward current. Together, these findings support a model in which parallel serotonin circuits selectively regulate feeding in response to internal energy needs or to external, hunger-independent cues.