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Suprachiasmatic nucleus

Suprachiasmatic Nucleus (SCN) Overview – Located in the hypothalamus above the optic chiasm – Acts as the circadian pacemaker in mammals – Contains approximately 10,000 […]

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Suprachiasmatic Nucleus (SCN) Overview
– Located in the hypothalamus above the optic chiasm
– Acts as the circadian pacemaker in mammals
– Contains approximately 10,000 neurons
– Divided into ventrolateral and dorsolateral portions
– Receives light input from the retina
– Critical for maintaining the internal body clock and regulating the sleep-wake cycle

Circadian Clock and Regulation
– Circadian rhythms present in various organisms
– SCN crucial for generating circadian rhythms in mammals
– Synchronizes slave oscillators in the body
– Light input entrains the SCN to the 24-hour cycle
– Regulates metabolic processes, circadian behaviors, photoreception, and thermoregulation in vertebrates
– Studies on clock genes like Clock (Clk) and Period2 (Per2) influence circadian rhythm

SCN Function in Endothermic and Ectothermic Vertebrates
– Endothermic animal circadian rhythms not influenced by external temperature
– SCN of ectothermic animals like the ruin lizard affected by temperature
– SCN plays a role in behavioral differences in vertebrates
– Evolutionary relationships exist between endothermic and ectothermic vertebrates
– SCN interacts with various brain regions and contains different peptides and neurotransmitters

Genetic Basis and Electrophysiology of SCN
– Neurons in the SCN exhibit synchronized circadian rhythms
– SCN functions as the central circadian pacemaker in mammals
– Genes like Clock and Bmal1 encode positive activators regulating gene transcription
– SCN neurons fire action potentials in a 24-hour rhythm
– SCN synchronizes nerve impulses to regulate body cells and drive glucocorticoid output

Clinical Implications and Disorders
– Disruptions or damage to the SCN can lead to mood and sleep disorders
– SCN functional disruption seen in early Alzheimer’s Disease stages
– Alzheimer’s patients suffer from insomnia, hypersomnia, and sleep disorders
– Major Depressive Disorder linked to altered circadian rhythms
– Study shows disturbed SCN rhythms in mice lead to anxiety-like behavior, weight gain, and despair

Suprachiasmatic nucleus (Wikipedia)

The suprachiasmatic nucleus or nuclei (SCN) is a small region of the brain in the hypothalamus, situated directly above the optic chiasm. It is the principal circadian pacemaker in mammals, responsible for generating circadian rhythms. Reception of light inputs from photosensitive retinal ganglion cells allow it to coordinate the subordinate cellular clocks of the body and entrain to the environment. The neuronal and hormonal activities it generates regulate many different body functions in an approximately 24-hour cycle.

Suprachiasmatic nucleus
Suprachiasmatic nucleus in green
Latinnucleus suprachiasmaticus
NeuroLex IDbirnlex_1325
Anatomical terms of neuroanatomy

The idea that the SCN is the main circadian pacemaker in mammals was proposed by Robert Moore, who conducted experiments using radioactive amino acids to find where the termination of the retinohypothalamic projection occurs in rodents. Early lesioning experiments in mouse, guinea pig, cat, and opossum established how removal of the SCN results in ablation of circadian rhythm in mammals.

Moreover, the SCN interacts with many other regions of the brain. It contains several cell types and several different peptides (including vasopressin and vasoactive intestinal peptide) and neurotransmitters.

Disruptions or damage to the SCN has been associated with different mood disorders and sleep disorders, suggesting the significance of the SCN in regulating circadian timing

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