The Root of Thought by Andrew Koob Read Free Book Online Page A

look like ice cream sprinkles when they migrate toward an area of infection. They can be considered the Red Cross of the brain.
    However, the cell that has provided such startling discoveries recently is the astrocyte (see Figure 4.1 ). The astrocytes are the cities to the neuronal highways. This cell is different functionally from the otherglial cells. The astrocyte is the most abundant cell in the human cortex and was first described by Otto Deiters (1834–1863) in an unfinished manuscript in the 1850s. Deiters died at the age of 29, and it was another former student of Johannes Müller—Max Schulte (1825–1874)—who published it for him. Deiters supported Virchow’s view that the cells were simply connective tissue. He described the flat star-shaped cells with many processes in the white and grey matter.

FIGURE 4.1 On the left are drawings of neurons in the cortex by Cajal. On the right is a closer view of astrocytes (dark, spidery cells) hanging out next to neuron cell bodies (pale cells with axons extending up).

     
    Jakob Henle (1809–1885), who was also a student of Müller’s, believed that the cells were active, functional units in the brain. In 1856, Virchow wrote that Henle was blocking his concept of glia as connective tissue simply to serve “his own interests.” In 1869, Henle published his first drawing of these cells.
    Later, Golgi conducted studies with his stain where he claimed glia contact with the blood vessels and neurons. Golgi’s discovery of the astrocyte’s contact with the blood vessels would be the beginning of his idea that the function of astrocytes is to provide nourishment for neurons.
    Cajal was quick to discount Golgi, but he had no idea about the nature of astrocytes himself. In his struggles with glia, he once wrote, “What is the function of these glial cells in neural centers? The answer is still not known and the problem is even more serious because it might remain unsolved for many years to come until physiologists find direct methods to attack it.”
    The word astrocyte sounds like an intergalactic parade, and it was used to demonstrate the star-shaped cells. Michael von Lenhossek (1863–1937) came up with the term in 1891 to describe the “neuroglia.” Neuroglia was a vogue term in the nineteenth century as the neuron was being put on the pedestal. Neuroglia meant everything except for neurons. However, they mainly referred to astrocytes as they were abundant, and oligodendricytes had not been discovered yet. Astrocytes were also previously called “spider cells.” German pathologist Edgar von Gierke (1877–1945) called the term inadequate because “nobody has seen a spider with as many feet as these cells have processes.” Lenhossek thought all glia should be termed spongicytes and divided into subsets, one of which would be astrocytes.
    Some cells believed to be related to astrocytes are Bergmann glia in the cerebellum. Their processes are found in the synaptic layer and their cell bodies sit next to neural ganglion cell bodies. Also in the cerebellum and olfactory bulb are velate astrocytes, which ensheath tightly packed neuronal cell bodies like a veil. Fibrous astrocytes are found in the white matter around axons and adjacent to oligodendrocytes. These cells might be different functionally, but currently because of their appearance, we know they are astrocytes. It might be possible that they communicate with each other, but this has not been determined.
    Astrocytes of the cortex, mainly astrocytes referred to as “interlaminar” and “protoplasmic,” are currently studied in relation to neuronal signaling. They look like octopi or stars. The extending feet that reach out to blood vessels comprise about 80 percent of the cell. No neural surface is left unexplored.
    When looking at animals up the evolutionary ladder—the oldest fossil being about 600 million years old—we can see the difference in the behavior related to glial cells.
    In the jellyfish,