According to the scientists, ghrelin, which is synthesized in the gastrointestinal tract, helps the body to adjust its internal sleeping and waking patterns to the daily rhythm of the outside world. The results were published in the I.M. Sechenov Russian Journal of Physiology.
Ghrelin is a peptide hormone produced by the stomach lining. It affects cognitive performance, learning and memory and stimulates hunger. Its concentration in the blood increases when a person sees and hears the smell of food, so ghrelin is called "hunger hormone" and "appetite hormone", said experts from the S.P. Korolev Samara National Research University at Samara University.
Scientists discovered that another function of ghrelin in the mammalian body is the adjustment of the biological clock to the external 24-hour astronomical day. The so-called suprachiasmatic nucleus, located in the main generator of circadian rhythms – the hypothalamus – is responsible for this synchronization.
"The main mechanism of regulation of circadian rhythms is photic: it is based on what a person sees outside the window, how much light hits the retina at a certain time of day," said Elena Inyushkina, study co-author and associate professor of the Department of Animal and Human Physiology at Samara University.
"Some other, non-photic mechanisms use information about diet, composition and energy value of food." Ghrelin works in accordance with the non-photic mechanism, added the researcher.
The team of scientists found that this hormone affects the nerve impulses transmitted from neuron to neuron through synaptic communication adhesions. "We examined rat brain slices and found that 50 out of 81 neurons showed activity in response to ghrelin administration," the researcher explained. "A more detailed study showed that the effect of ghrelin on neuronal spike activity is through GHS-R1a receptors, which are also involved in the body's anti-inflammatory response."
After ghrelin was introduced, 32 percent of neurons showed increased activity. But by contrast 30 percent were "inhibited", indicating that ghrelin acts differently on different parts of the brain, Inyushkina added.
The work was conducted with support of the Russian Science Foundation.