We know how circadian rhythms work in the brain, what about the body?

        Circadian rhythms are an essential part of mammalian function, with the routine of light and darkness controlling multiple factors like hormone release, appetite, digestion and body temperature. The course of this light/dark cycle is over the course of 24 hours which allows organisms to strategically distribute these mechanisms for the optimal functioning of survival. This became known as the circadian clock network, which consists of a series of behavioral functions that are shown across organisms. The research done by Dr. Daniel Cavanaugh (Cavanaugh, 2024) in the article Overlapping Central Clock Network Circuitry Regulates Circadian Feeding and Activity Rhythms in Drosophila has provided evidence that specific neural alterations in specific cell regulations can affect feeding and locomotor regulations. In lateral clock manipulation, which is located in the lateral entorhinal cortex and interprets the perception of time in mammals, alters the timing of synchronized feeding schedule and the associated locomotor functions before or after said feeding. On the contrast, dorsal clock manipulation, which is located in the protocerebrum and control the 24-hour associated cycle of the day, affect the rhythm of overall tasks throughout the day. This article discerns the differences between these two areas of function, feeding and activation throughout the day, and the effects these manipulations can have on the overall disruption of the circadian rhythm. 

        This effect of systematic function and direct alterations affect rhythmic functions can be seen across humans as well. The article Clock-in, clock-out: Circadian timekeeping between tissues published at the University of California-Irvine, (Smith, 2020), explores how specific tissues must be in sync with each other in order for this process to occur. Light is cited as the “zeitgeber”, or the cue, for the entire process to occur. The suprachiasmatic nucleus (or SCN) is a small structure located in the hypothalamus that regulates the synchronization of the circadian rhythm, interprets light/lack of light through the retinas and adjusts each factor accordingly. Through various connections, the SCN can communicate with other brain areas (such as the prefrontal cortex, the pituitary gland and nearby endocrine glands) in order to ensure proper functions in the entire body. This system is noted as a hierarchy, with the SCN clock at the top because it not only begins and ends the process but also has direct communication with each element of the entire process.  

        One major aspect of this function that is also highlighted in this paper is how important the peripheral tissues, which includes areas such as the liver, specific muscles and fat cells, are throughout the process of feeding cycles. This paper has identified several “peripheral clocks”, which are biological clocks that are still regulated outside of the brain’s circadian clock. The hormone glucocorticoid is released by the adrenal glands in areas around the kidney and liver. The signals to begin the release and the specific amount of glucocorticoid to release are directly imported from the SCN, and the resulting binding to specific receptors is a direct factor in the feeding cycle of the organism. As an indirect result of this, the sleep-wake cycle is also affected by this, since feeding/consumption is directly associated with daytime (or when sunlight is present). This creates a domino effect for other peripheral clocks that are essential to be in sync during the sleep-wake cycle. Because of the increase in food intake, a specific clock called the “pancreatic clock” becomes activated and releases insulin to account for the spike in blood sugar. As a result, it becomes a direct influence on the circadian cycle because it affects the peripheral clocks of metabolic output.  

        Overall, the circadian rhythm is often restricted to the specific functions of the brain, when it encompasses a drastic number of functions throughout the body. Future research hopes to explore the direct communication between these peripheral clocks and how circadian rhythm is regulated throughout the body.  

                                                    References  

Cavanaugh, D. et. al. (2024) Overlapping Central Clock Network Circuitry Regulates Circadian Feeding and Activity Rhythms in Drosophila. Journal of Biological Rhythms. 39(5), 440-462.https://loyolauniversitychicago-my.sharepoint.com/personal/rmorrison_luc_edu/_layouts/15/onedrive.aspx?ga=1&id=%2Fpersonal%2Frmorrison%5Fluc%5Fedu%2FDocuments%2FTeaching%20%2D%20Onedrive%2FNEUR%20300%20%2D%20Neuroscience%20Seminar%2FNEUR%20300%20%2D%20Spring%2025%2FNEUR%2F%2801%2E28%2E25%29%20%2D%20Dan%20Cavanaugh%2Fsaurabh%2Det%2Dal%2D2024%2Doverlapping%2Dcentral%2Dclock%2Dnetwork%2Dcircuitry%2Dregulates%2Dcircadian%2Dfeeding%2Dand%2Dactivity%2Drhythms%2Din%2Epdf&parent=%2Fpersonal%2Frmorrison%5Fluc%5Fedu%2FDocuments%2FTeaching%20%2D%20Onedrive%2FNEUR%20300%20%2D%20Neuroscience%20Seminar%2FNEUR%20300%20%2D%20Spring%2025%2FNEUR%2F%2801%2E28%2E25%29%20%2D%20Dan%20Cavanaugh 

Smith, J. et. al. (2020). Clock-in, clock-out: Circadian timekeeping between tissues. Journal of Biological Clocks. 32(4). 345-350. https://watermark.silverchair.com/bio042020007.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAABFEwggRNBgkqhkiG9w0BBwagggQ-MIIEOgIBADCCBDMGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMr6C02hkG4WK1nhUsAgEQgIIEBEvajMYI4BrV-18mTc52c5BWkX0FQsUvvCOB6lQZcx5NEp0VfXwjsEa4Q7IYjpkjoXCVH6yx4ZgEy1OqHkgVUv5KOiHrm6dr8Z3hW0LPUU_PLAK_Tye35mSkYauKXNmL2V-YY7B43dTsLMXnnWn140t6t1_CUNwJfq17aqjxydEfnBK0wos7QZSMs38psq0r5Uou5SHOPpKrHtY7PK1G54AI9-zv61mjBmrtP4I9ZhKbbx4SuvQaYvloac2ckYRVqQTK1XFzISZ-6lnbTGANTgjQCj4UYAJp66a_BjyB8Ot54pZtu7ttyQpVwq0q7-ESQEYF4aEHivFGGXryFNoDqW3w6ZvmB9v9HYWJgX0xlVsfnPoiKzS6_rYvHm-zDcbid3NBrTSi8guQ9eoTX_JPu-pEQ_40kYtNYcerE3vTdhSsqz_R5okl63-lBdayjyci7aJc0a6Z-t8d1EXc-TxIUidIlQVW6z7ncMAw6Y0ifF8IFzLSO_0B5jeP_55PzHGiyMy7dT7mabd0pfV_M9n951UQD6I0EHFf-JakFSXjV7H7TptE_dYrZ4Zaf9xVOAzad8cvWV4FrWI_VmlLPyQp7hcLoTfIYrYn9jYn8nHbNZ96UDroMTM0qP2-daCfvB5xbljgF3gz_A-nDQG1vn1LynCwuulhNu1u8WlrwFdODwK4fgmDpIJTIXO5o4hdzYjlhNkZ1NZDt58GhLlGx-bLi8xL4RMWZ80Vq6cvKM0WsHPbAsg70gZwlDN9R2fDJpsdIjA32XskX9ejg_-3fcdPR7HwU4iuT4U1SBZ55TB3kQTZpNjTNIWGPbHgM3oj0VJcS70WgwcZoouEHWcpHfWHy6_GdSrIbFC3CgvdpSYv_mBeizmTGv9rBrjRV1ABUBOWR_F7vMrZotdsv1j82VsUmTkoNc9dEr_k9KfCmhLB2vrHfyp0O23FuDp2BN-dVN7L6tt3p-0-j9FrRUlEx18jp7CRZZdskD9C2VZlDr5Q6MTe_NRQ4WFy1SQ60FRMQ38K-fQhPcqUOVljVqEAIDRHM1gGt5FTETQ0TgmWnqTVtdmlzZISZmNdHxCGll_0T1Am5jv2f9GxjqTxm9-jTTWcKK49oZev5rLpDxpU60fBz-xAo8wOciy_t6dn737ePPnaAHJZsoIl5asnwyIFdEvANDQXn4cQzGmNxtW8lB_5voYbP5CTbEy3Ywg0WLde3hsGXdRs0PyAOSSHfKrhoJvEit7WHJyFcFFbckYJuJUdS6D6fVOINu4uLoIlVIREnQ4j2Kbycy6gt9_H8YmXfIVLzAf2zZedmH2L9lDf-5ojIeMK8rKCUkn_bfYDoWoU1tro-gGOc5cC9nY9wkyCsZ0jDLoq5k21