Suprachiasmatic nucleus

The suprachiasmatic nucleus ( Suprachiasmatic nucleus, SCN, English: suprachiasmatic nucleus ) is a core area in the brain, more specifically in the ventral hypothalamus of mammals. In the adjacent diagram is an example of the field mouse shown, where the nucleus is located suprachiasmatic. The approximately 800 microns wide area below the III. Cerebral ventricles and on the crossing of the optic nerve ( optic chiasm ). For photo opposite a preparation made ​​from the red marked area. In the center is (dark, vertical bar) to see the ventricle ( 1) and including two pear-shaped densities of stained cells (2). The dark horizontal area at the bottom third of the picture is the junction of the optic nerve (3).

It is now accepted that the " master clock ", ie the circadian rhythms controlling localized "internal clock " of the mammals in this area. Lesions of this structure lead to a loss of rhythmic behavior, such as the sleep-wake rhythm can. However, not all the rhythms fall in a mammal (including humans ) under the control of the SCN. One can therefore assume that there are other internal clocks that operate in parallel or can be influenced by the SCN.

Case of an isolated SCN tissue that is still viable in a suitable culture medium, rhythmic metabolic reactions can be observed even in vitro.

The immediate location of the SCN to the optic nerve is not a coincidence. If the optic nerve is severed before the SCN - reach the area that is on the tract retinohypothalamicus no pulses of a light - dark cycle more - is also an entrainment of the rhythm no longer possible. A cut after the crossing of the optic nerves, however, has no influence on the synchronization with a light -dark cycle.

Further evidence for the localization of the circadian clock in the SCN transplantation experiments with SCN tissue in hamsters. Here it was possible to the rhythm of a " short-day hamsters " to transplant reversed to a " long-day hamsters " and.

  • Chronobiology
  • Heartland