Question

The Paraventricular nucleus of the hypothalamus (PVN) is important in two output systems of the SCN: Melatonin and glucocorticoids (cortisol) production. Describe how these systems are regulated (by other hormones?). Also describe how the SCN is involved in the circadian production of these two hormones. What are the respective functions of these hormones?

Answer 1

• Estrogen has pronounced effects on circadian activity rhythms, likely through both direct effects on the SCN and indirect mechanisms. In females, estrogen modulates both period and activity consolidation, suggesting actions on the circadian clock rather than transient effects on SCN targets.
• In males, testosterone also affects consolidation of locomotor activity rhythms. Testosterone may act through SCN androgen receptors.
• Growth hormone, essential to the repair and restoration processes of the body, is also secreted during sleep, particularly during deep non-REM sleep.
• The most important hormones affected by the circadian clock, at least insofar as they affect sleep, are melatonin (which is produced in the pineal gland in the brain, and which chemically causes drowsiness and lowers body temperature) and cortisol (produced in the adrenal gland, and used to form glucose or blood sugar and to enable anti-stress and anti-inflammatory functions in the body).
• The body’s master clock, or SCN, controls the production of melatonin, a hormone that makes you sleepy. It receives information about incoming light from the optic nerves, which relay information from the eyes to the brain. When there is less light—like at night—the SCN tells the brain to make more melatonin so you get drowsy.