Human evolution: vagus nerve, liver and urge to eat (Introduction)

by David Turell , Friday, November 08, 2024, 17:53 (13 days ago) @ David Turell

As noted before, the vagus nerve is in control of liver hunger stimulation:

https://www.sciencemagazinedigital.org/sciencemagazine/library/item/08_november_2024/42...

"The hepatic vagal nerve mediates the impact of circadian disruption on food intake in mice

"Timing mechanisms have evolved across all kingdoms of life to anticipate daily changes in the light environment and to optimize opportunities for nutrition. In mammals, the central circadian clock in the hypothalamic suprachiasmatic nucleus synchronizes to external light. However, other cells, tissues, and organs in the body have their own circadian clocks. For example, the liver has a molecular clock that can be entrained by feeding-fasting cycles. Desynchrony between the light-entrained suprachiasmatic nucleus and the food-entrained liver carries adverse health consequences, including increased risk of cardiometabolic diseases or type 2 diabetes; yet, how these clocks become misaligned remains unknown. On page 673 of this issue, Woodie et al. report a neural link from the liver to the brain that conveys the misalignment signal to drive changes in eating behavior, body weight maintenance, and energy metabolism. This reveals a potential therapeutic target to mitigate the metabolic impact of circadian disruption.

"Mammalian circadian rhythms are set by cues that initiate a transcription-translation feedback loop involving activators [such as BMAL1 (basic helix-loop-helix ARNT-like protein 1)] and repressors [such as REV-ERBs (reverse c-erbAa)]. Deletion of the core clock components REV-ERBα and REV-ERBβ in adult mouse hepatocytes disrupts circadian changes in gene expression and liver function.

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"Food intake is regulated by a complex central neuronal system, primarily involving hypothalamic centers located at the base of the brain. Of particular importance is the arcuate nucleus of the hypothalamus, which has a key role in controlling food intake. Indeed, in mice lacking REV-ERBα and REV-ERBβ in liver cells, the circadian organization of the arcuate nucleus in the hypothalamus was disrupted, confirming that rhythmic activity in this important feeding center requires a rhythmic liver.

"The central metabolic circuitry is regulated by numerous endocrine and neural inputs. The common hepatic branch of the vagus nerve is a two-way highway of communication between the brain and liver, regulating many aspects of food intake and metabolism. Fibers in this region transmit information on liver function to the brain.

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"This finding supports the hypothesis that afferent vagal signaling is a key mediator for the desynchronized liver clock. It also underscores the vital role of the liver-brain axis, which requires an intact hepatic vagus nerve, a pathway previously shown to be crucial in controlling metabolic functions, such as glucose homeostasis.

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"Notably, transection of the hepatic vagal branch reduced calorie intake to that observed during the animal’s active phase, reduced overall calorie intake, and prevented the development of obesity. This intervention provides a mechanistic explanation for the experimentally observed beneficial effects of timerestricted feeding in mice and time-restricted eating in people.

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"The implication of the findings of Woodie et al. is that the circadian-disrupted liver sends signals to the arcuate nucleus to drive disordered eating and that this circuit explains the obesity seen in response to prevalent human circadian and sleep disruption (such as shift work)."

Comment: here we see a highly complex control of appetite. The purpose is proper weight control. Darwin style 'natural' evolution has no purpose. So how did this happen? This is obviously designed.