The Sweet Blockade
Actually, the aunt's slide show is boring, but her cream cake isn't easy to imitate. After the third piece of cake, your gaze suddenly wanders away from the slides. You can't concentrate anymore - poor aunt. Or can biology excuse the lack of attention? Whether we were hungry or tired, if our body didn't constantly call itself into our consciousness, we probably wouldn't be able to survive. The brain plays a crucial role here: it recognizes our power reserves, forwards the message and causes us to adapt our metabolism and our behavior to the energy reserves. In addition to hormones, a number of other metabolites help spread the message. Auntie's cake also had a signal that told the brain the three pieces of cake and perhaps invited it to be lazy: glucose. Scientists at the University of Manchester were investigating exactly how the three pieces of cake got around in the body.
Science has been learning for years. Researchers discovered glucose-sensitive neurons in the brain's hypothalamus, which are activated by the glucose in the brain fluid, the liquor, and then fire. Neurologists, however, are particularly puzzled by the neurons in which the sugar does not stimulate the conduction, but blocks it. This is the case with the orexin neurons, which go on strike when there is a lot of glucose in the CSF. The messenger substance orexin activates the neurons that control the body's appetite and sleep-wake rhythm. How important the neurons are becomes clear when they are missing - like those of narcolepsy patients. Denis Burdakov from the University of Manchester has set himself the goal of further researching the orexin neurons. He has now succeeded in explaining in detail how glucose manages to paralyze the neurons.
The researchers created genetically modified mice in which the orexin neurons form a fluorescent protein and thus become visible. The neurologists then cut the mouse brain into slices and exposed the nerve cells to glucose concentrations that fluctuated by the minute, which also occur in everyday mouse and human life. Biochemical and electrophysiological experiments allowed them to follow and finally analyze the excitation conduction on the neurons.
What Burdakov now concludes is surprising: Sugar obviously has no helpers outside of the nerve cell. The researchers believe that it is the glucose itself that binds to the outside of the nerve cell via receptors. A still unknown messenger then, stimulated by the bound sugar, transmits the signal to special potassium channels of the nerve cell, so-called tandem pore channels. This causes these channels to open, allowing potassium ions to rush out of the cell and preventing it from firing. Interestingly, neither the energy carrier ATP nor the glucose or calcium concentration in the cell seems to play a role in signal transmission. However, the opening and closing of the channels is regulated - for example by the acidity of the brain. The cells also sometimes fire less, sometimes more, depending on how much glucose finds its way to the nerve cell.
So the orexin neurons are the brain's sugar sensor - but also more. Somehow they sometimes turn our consciousness inside out - even if this doesn't always seem to happen with decency, may my aunt forgive me.
