All About Gastrointestinal Signaling

Gastrointestinal (GI) neural and hormonal signals to the brain alter mood states, appetite, and feeding behaviours. These pathways are an emerging area of investigation that has only begun to be explored in rodents. Such information will be crucial for developing novel therapies for GI disorders that may be better tolerated than centrally acting drugs such as antidepressants or psychostimulants. Sensory, gastrointestinal signalling, and gastrointestinal (GI) neural and hormonal signals to the brain alter mood states, appetite, and feeding behaviours. These pathways are an emerging area of investigation that has only begun to be explored in rodents.

About Gastrointestinal Signaling

Gastrointestinal (GI) sensory, neural, and hormonal signals to the brain alter mood states, appetite, and feeding behaviours. These pathways are an emerging area of investigation that has only begun to be explored in rodents. Such information will be crucial for developing novel therapies for GI disorders that may be better tolerated than centrally acting drugs such as antidepressants or psychostimulants.

Sensory, Gastrointestinal Signaling

Sensory, gastrointestinal signalling is when gastrointestinal (GI) neural and hormonal signals are sent to the brain and subsequently alter mood states, appetite, and feeding behaviours. These pathways are an emerging area of investigation that has only begun to be explored in rodents.

Sensory, Gastrointestinal Signaling Pathways:

There are three major pathways by which sensory and gastrointestinal signalling occurs. The three major pathways are: 

(1) The vagus nerves innervating the GI system send continuous information to the brainstem and hypothalamus.

(2) The brainstem and hypothalamus in turn project to the higher centres in the Limbic System; and (3) inputs are sent to a variety of regions in the Limbic System.

Sensory, Gastrointestinal Signaling in Brain:

Various brain regions are involved in sensory, and gastrointestinal signalling (SGIS). The exact locations vary depending on what type of information has been received. After a meal or upon sensing caloric content in the GI tract, inputs are sent to the ventral tegmental area (VTA), nucleus accumbens (NAc), amygdala, and prefrontal cortex (PFC) that result in feelings of reward and euphoria. Following a period of starvation or fasting, inputs are sent to the hippocampus, PFC, and hypothalamus that result in feelings of withdrawal, depression, and anxiety.

Hormonal Signaling

In the gastrointestinal system, several hormones have been shown to play a role in the regulation of satiety, muscle contractions, ingestion of food, and digestion. Thus, hormonal signals from the gut are important for controlling hunger, satiety, and other physiological functions.

There are many neurotransmitters in the nervous system, and among them, serotonin, acetylcholine, norepinephrine, dopamine, GABA, and epinephrine are important for gastrointestinal function. In addition to these known neurotransmitters, recent research has begun to delve into the role that other compounds such as endocannabinoids have on the gastrointestinal system. While there is preliminary evidence of their role in regulating GI processes, more extensive studies are needed to elucidate this role. 

1. Acetylcholine: Acetylcholine plays an important role in the gastrointestinal system and can be thought of as a neurotransmitter involved in both smooth muscle and nerve function. Thrill-like activity has been recorded in certain areas of the GI tract during chewing or eating, indicating that acetylcholine is involved in the perception of pain. 
2. Norepinephrine: Norepinephrine is a neurotransmitter involved in regulating the gastrointestinal system. Studies have shown an increase in gastric acid secretion with norepinephrine infusion. In addition, norepinephrine can stimulate glandular secretion.
3. Dopamine: Dopamine is a neurotransmitter involved in regulating the gastrointestinal system. It is involved in the suppression of gastric acid secretion and motility.
4. GABA: GABA is the primary inhibitory neurotransmitter in the nervous system. It plays an important role in regulating smooth muscle, blood vessels, and nerves. Studies have shown that GABA is involved in regulating gastrointestinal motility.
5. Epinephrine: Epinephrine is a neurotransmitter that regulates the gastrointestinal system. It has been shown to increase the rate of gastric emptying and the gut filling capacity.

Neural Signaling

In the gastrointestinal system, neural signalling is important for controlling hunger and satiety. Hormones secreted by the gut, such as glucagon-like peptide-1 (GLP-1), glucagon, cholecystokinin, and peptide YY affect satiety, glucose metabolism, and hormone secretion. GLP-1 is an incretin. Incretins are hormones produced in the intestine that act on the same receptors as insulin. GLP-1 slows gastric emptying and suppresses glucagon secretion, decreases blood glucose, and inhibits appetite. GLP-1 is derived from the proglucagon gene by posttranslational modification in enteroendocrine cells. Incretins, including GLP-1, help control appetite by increasing feelings of fullness and decreasing feelings of hunger after meals.

Conclusion

The study of sensory, and gastrointestinal signalling provides a new area of investigation and research tool for studying various aspects of depression, obesity, and disorders related to cognitive impairment. Understanding the neural and hormonal signals of the GI tract that regulate mood states, appetite, and feeding behaviour may provide a means of developing novel treatments for disorders of these processes. Gastrointestinal disorders can present with a variety of symptoms associated with a disruption to sensory, and gastrointestinal signalling. The main reason for this postulation is that the majority of patients with GI disorders suffer from psychological distress, which can be alleviated by centrally acting drugs.