The discovery and surgical application of general anesthesia by the American physician Crawford Williamson Long in 1849 was surely one of the great miracles of science and medicine , allowing millions of human beings to have undergone the most atrocious operations without feeling pain
However, although we have been using it since then, scientists did not know the exact mechanisms of its operation. Finally, a recently published Duke University study has found that drugs used as anesthetics hijack the neural circuits that make us sleep to knock us out for a few hours. In short, they have found that general anesthesia induces unconsciousness by appropriating the neural circuits that lead us to sleep. The Duke University team traced this neural circuit to a group of cells at the base of the brain responsible for producing hormones to regulate body functions, mood and sleep. The finding could be used to invent more effective sleeping pills capable of putting patients to sleep with fewer side effects.
Since the first patient was operated on under general anesthesia in 1849, scientists have been trying to figure out exactly its mechanisms. The prevailing theory has been that many of these drugs disrupt normal brain activities and cause an inability to move or feel pain . Other theories revolved around sleep, the state most similar to general anesthesia. However, research over the last decade has shown that sleep is a more active process than previously thought, with entire sets of neurons firing while we are sleeping.
Fan Wang, a professor of neurobiology at Duke University School of Medicine, and Li-Feng Jiang-Xie, a student in her lab, thought that the prevailing view of general anesthesia was too biased and that perhaps, instead By simply inhibiting neurons, anesthetics could also activate certain neurons in the brain. To test their theory, Jiang-Xie and Luping Yin, a postdoctoral fellow in Wang’s lab, applied general anesthesia to mice with several different commonly used drugs . They then used molecular markers to track the neurons that were most commonly activated by anesthetics. Among them they found a group of neurons buried in a small region of the brain called the supraoptic nucleus, which has long projections that release large amounts of hormones such as vasopressin directly into the bloodstream.
Cells that connect the nervous and endocrine systems
“Most of the cells activated by anesthesia were hybrid cells that connect the nervous system and the endocrine system. That surprised us and led us to investigate uncharted territory to understand the neural pathways of general anesthesia,” according to Jiang-Xie. The researchers then used a sophisticated technique developed in Wang’s lab to activate or deactivate this specialized group of cells with chemicals or light. When they activated the cells of the mice, the animals stopped moving and fell into a deep sleep. waves , usually associated with unconsciousness. They then proceeded to eliminate this group of cells and the mice began to move and were unable to fall asleep. artificially pre-activated neuroendocrines made them remain subject to to the effect of anesthesia for longer periods of time. Conversely, when these cells were silenced, the mice awoke from anesthesia more easily.
This study also revealed an unexpected role for hormone-secreting cells in the brain in promoting deep sleep. Many people, especially those with Alzheimer’s, have a hard time falling asleep, but current medications have troublesome side effects. The researchers believe that if they can find ways to manipulate this neural circuitry, perhaps targeting hormones or small peptides, more efficient sleeping pills could be developed.
