In 1895, Hungarian neurohistologist Mihály Lenhossék, aka Michael von Lenhossék, coined the term “astrocytes,” which means “star cells” in Greek, to describe the multi-limbed structures he and others have seen in brain tissue human under the microscope.
Although abundant, astrocytes have escaped the notice of neuroscientists, who instead focused on neurons. “Historically, of course, because neurons are electrically excitable cells,” they were easier to detect and record, says Yongjie Yang, professor of neuroscience at Tufts University in Boston, Massachusetts. Non-neuronal cells, called glial cells, were considered secondary.
Over time, it became clear that astrocytes help maintain homeostasis in the brain. Their appendages, called processes, have “terminal feet” that wrap around blood vessels to prevent molecules from passing through, forming part of the blood-brain barrier. Astrocytes also help to scaffold neurons; scavenge excess neurotransmitters, ions and reactive oxygen species; produce glycogen to feed neurons; and, if there is a brain injury, migrate to the site and surround it with protective scar-like tissue.
Scientists have long thought astrocytes were “silent”, says Yang, but now appreciate that they communicate – by altering levels of calcium ions through surface ion channels in conjunction with organelles – in response to stimuli. .
Astrocytes talk in other ways, too: They, or the chemicals they produce, must be there to guide neuronal growth, telling synapses when and how to form, according to a 2005 study, and eliminating those that don’t. are not necessary. Throughout this process,[astrocytes] release different signals, corresponding to developmental time,” says Nicola Allen, associate professor of molecular neurobiology at the Salk Institute in La Jolla, California.
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