Sleep!

Sleep is an important part of our daily routine, we spend one-third part of our day sleeping(A Sehgal et al), but have you ever wondered why do we feel sleepy? what happens when we sleep? how is sleep regulated? What would happen if you don’t sleep for some days consecutively?

Sleep is regulated by circadian rthymn, Circadian rhythms are biological processes that endogenously oscillate with a period of 24 h. It is just like a clock present inside our body but it's complicated, owing to the fact that it is synchronized by feeding patterns, light, temperature. The central circadian pacemaker is in the suprachiasmatic nucleus (It is present in the hypothalamus which is in the brain) in mammals, other cells(Jennifer A Mohawk et al), including the cells of the Blood-Brain barrier (It is a functional separation between circulating blood and central Nervous system), have circadian rthymn driven by molecular clocks. The Blood-brain Barrier (BBB) permeability is controlled by sleep and circadian rthymn. 

When we sleep, endocytosis across BBB is increased(Artiushin et al), endocytosis is a process by which cells take up molecules inside the cell. Now just imagine you have ordered food from Zomato but to eat the food you need to open the door, take in the food inside then eat similarly cells take up molecules by endocytosis but in this case, the door is the receptor present on the cell membrane. The molecules taken up by BBB via endocytosis are leptin, TNF-α, cytokines to name a few(VA Cuddapah, et al). When endocytosis doesn’t occur, we feel sleepy(VA Cuddapah, et al), so the next time you feel sleepy it’s because endocytosis is inhibited. It was also found that endocytosis occurs highest early during the night and lowest early in the morning.

Sleep also promotes the clearance of metabolites out of the brain(VA Cuddapah, et al). During sleep, the interstitial spaces of the brain are larger, allowing for a more robust movement of metabolites. Accumulation of β-amyloid in the brain aggregates to form plaques that lead to Alzheimer’s disease. β-amyloid was found to accumulate in interstitial fluid during wakefulness and after sleep deprivation, even if it’s just 1 night of sleep deprivation(Ehsan Shokri-Kojori et al). β-amyloid is cleared through multiple routes. An age-related decline is observed in the clearance of β-amyloid; this can be due to loss of sleep given that older individuals sleep less and have decreased quality of sleep((VA Cuddapah, et al).

To conclude, sleep is a highly regulated process and I hope you get a good night’s sleep.

To Read More: 

1. Hirofumi Toda et al A sleep-inducing gene, nemuri, links sleep and immune function in Drosophila 10.1126/science.aat1650
2. Jennifer A Mohawkh et al Central and peripheral circadian clocks in mammals 10.1146/annurev-neuro-060909-153128
3. Vishnu Anand Cuddapah et al Regulation of Blood Brain Barrier by Circadian rtymns and sleep  https://www.cell.com/trends/neurosciences/fulltext/S0166-2236%2819%2930060-8
4. Ehsan Shokri-Kojori et al β-Amyloid accumulation in the human brain after one night of sleep deprivation https://doi.org/10.1073/pnas.1721694115
5. Gregory Artiushin et al Endocytosis at the Drosophila Blood Brain Barrier as a function of sleep https://doi.org/10.7554/eLife.43326.001