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New Brain Mechanism Controlling Growth hormone Release Discovered
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Neuroscientists from the University of California, Berkeley and Stanford University have explored brain circuits that control growth hormone release during sleep and discovered a new feedback mechanism in the brain that keeps growth hormone levels finely balanced. This mechanism could open avenues for treating people with sleep disorders tied to metabolic conditions like diabetes, as well as degenerative diseases like Parkinson’s and Alzheimer’s.
Sleep is known to promote tissue growth and regulate metabolism, partly by enhancing growth hormone (GH) release, but the underlying circuit mechanism is unknown. Ding et al.demonstrate how GH release, which is enhanced during both rapid eye movement (REM) and non-REM (NREM) sleep, is regulated by sleep-wake-dependent activity of distinct hypothalamic neurons expressing GH-releasing hormone (GHRH) and somatostatin (SST). SST neurons in the arcuate nucleus suppress GH release by inhibiting nearby GHRH neurons that stimulate GH release, whereas periventricular SST neurons inhibit GH release by projecting to the median eminence. GH release is associated with strong surges of both GHRH and SST activity during REM sleep but moderately increased GHRH and decreased SST activity during NREM sleep. Furthermore, Ding et al.identified a negative feedback pathway in which GH enhances the excitability of locus coeruleus neurons and increases wakefulness. Image credit:
Understanding the Growth Hormone Regulation
Sleep plays a crucial role in tissue growth and metabolic regulation, largely due to the increased release of growth hormone (GH) during sleep. However, the precise brain circuits responsible for this process remained largely unknown. Recent research has shed light on this mechanism, revealing a complex interplay between different types of neurons in the hypothalamus.
Key Players: GHRH and Somatostatin
The study identified two key players: neurons expressing Growth Hormone-Releasing hormone (GHRH) and neurons expressing somatostatin (SST). These neurons have opposing effects on GH release:
- GHRH neurons: Stimulate the release of GH.
- SST neurons: Suppress GH release by inhibiting GHRH neurons.
Researchers found that SST neurons operate in two distinct areas:
- Arcuate nucleus: SST neurons directly inhibit nearby GHRH neurons.
- Periventricular area: SST neurons project to the median eminence to inhibit GH release.
Sleep Stage Differences
The activity of these neurons varies depending on the sleep stage:
- REM sleep: Strong surges of both GHRH and SST activity are observed.
- NREM Sleep: Moderately increased GHRH activity and decreased SST activity are observed.
The Negative Feedback Loop
A significant finding of the study is the identification of a negative feedback loop. growth hormone itself influences wakefulness:
GH enhances the excitability of neurons in the locus coeruleus, a brain region associated with wakefulness, ultimately increasing wakefulness.
This feedback loop helps to maintain a delicate balance in GH levels, preventing excessive release and ensuring proper regulation.
Potential Therapeutic Implications
This discovery has significant implications for treating various conditions:
- Sleep Disorders & Metabolic Conditions: Understanding the GH regulation mechanism could lead to new treatments for sleep disorders linked to metabolic conditions like diabetes.
- Neurodegenerative Diseases: The findings may also offer insights into treating degenerative diseases such as Parkinson’s and Alzheimer’s, where sleep disturbances and metabolic dysfunction are common.
FAQ
Q: What is growth hormone and why is it significant?
A: Growth hormone is a hormone produced by the pituitary gland that plays a vital role in growth, cell regeneration, and metabolism.
Q: What are GHRH and somatostatin?
A: GHRH (Growth Hormone-Releasing hormone) stimulates GH release, while somatostatin inhibits it. They work in opposition to regulate GH levels.
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