1 The suprachiasmatic nucleus or nuclei (SCN) is a small region of the brain in the hypothalamus, situated directly above the optic chiasm. It is a biological circadian clock system of neurons that are responsible for controlling/modulating the synchronization and temporal organization of circadian rhythms in cells and tissues throughout the body.
Importantly, merely mimicking the phase relationship of circadian dopaminergic and serotonergic input signals to the clock as observed at a particular season by appropriately circadian timed daily injections of their precursors (L-DOPA and 5HTP, respectively) produce that seasonal physiology irrespective of the actual time of year of such treatment. That is to say, it is possible to shift animals back and forth between the seasonal insulin sensitive and resistant states by such treatment even when made at any time of year. The circadian neuroendocrine output signals from the clock function to create circadian stimulus (humoral hormone, neurotransmitter) and response (cellular hormone and neurotransmitter signal transduction apparatus) rhythms in peripheral tissues to synchronize metabolic activities within the organ systems of the body and keep the organism in sync with its cyclic environment. A simple example of such an organization is the peak in the daily rhythm of hepatic lipogenic responsiveness to insulin synchronized with the daily peaks in insulin release from the pancreas and feeding. In obese animals these rhythms are all in phase and the amplitudes of the insulin stimulus and response rhythms are elevated relative to lean animals wherein the peaks in the insulin stimulus and response rhythms are out-of-phase and diminished (Figure 2).
A small town on South Africa’s southern coast just finished construction of the country’s first “green” airport. From its control towers to its escalators, its baggage carousels to its ATMs, the regional airport in George, South Africa, will run exclusively on power supplied by 2,000 solar panels, . The panels have the capacity to supply up to 750kW each day, nearly twice the required 400kW. Any excess energy will be transferred to the municipal power grid, with a running clock inside the airport tallying the number of households powered by the system.
A series of studies conducted initially and primarily by the laboratory of Dr. Albert H. Meier and his colleagues at Louisiana State University in Baton Rouge, LA, between the years of the early 1960s to the late 1980s and subsequently to date by the laboratories of Anthony H. Cincotta, have shed light on the essence of vertebrate biological timing mechanisms responsible for control of seasonal peripheral fuel metabolism. To concisely summarize the half century findings of these laboratories, it was found that the annual cycle of metabolism in vertebrates was itself the manifestation of changing circadian phase (temporal) relationships of circadian neuronal oscillations in the brain that input to the biological clock pacemaker system (centered at the suprachiasmatic nucleus1 of the hypothalamus). This information is then processed and responded to by the SCN (suprachiasmatic nucleus) that then directs metabolic functions through direct communication with the neuroendocrine axis. The SCN clock system sends strong regulatory signals to the preautonomic fibers in the hypothalamus, to higher brain centers regulating autonomic function, and to the entire neuroendocrine system. A long series of studies led to the postulate that the changing phase relations of circadian dopaminergic and serotonergic neuronal input signals into the pacemaker clock system in the hypothalamus (centered at the suprachiasmatic nuclei) regulate the output signals from the clock that in turn regulate neuroendocrine programming of metabolism. For example, a circadian peak of dopaminergic input activity to the SCN at 12 hours after the circadian peak of serotonergic input activity to the SCN is coupled to one seasonal condition (obese/insulin resistant state) while a circadian dopaminergic input activity to the SCN at 0 hours after the circadian peak in serotonergic input activity to the SCN is coupled to another seasonal condition (lean/insulin sensitive state) (Figure 1)