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單一神經元可以釋放多種神經傳導物嗎？
Can one neuron release more than one neurotransmitter?
單一神經元可以釋放多種神經傳導物嗎？
—Marvin Shrewsbury, Wailuku, Hawaii
Rebecca Seal, a neuroscientist at the University of California, San Francisco, replies:
When discussing neurotransmitters, most people think of the classical neurotransmitters, such as dopamine and serotonin—the primary chemical messengers used by neurons to communicate with one another and with other types of cells. In the early 20th century physiologist Sir Henry Dale hypothesized that an individual neuron releases the same classical neurotransmitter from all its axons, the spindly branches that jut out from the main cell body. Another prominent scientist of the time, Sir John Eccles, restated Dale’s principle to also mean that a neuron releases only one neurotransmitter. From that point on, the concept of “one neuron, one transmitter” became widely accepted.
每每談到神經傳導物(neurotransmitters)時，大部分的人都會想到古典的神經傳導物，如多巴胺(dopamine)和血清張力素(serotonin)─等神經元用來和其他神經元或其他細胞溝通的初級化學傳訊者(primary chemical messengers)。二十世紀早期的生理學家(physiologist)Sir Henry Dale提出一個假說認為單一神經元的所有軸突都將釋放相同的神經傳導物質。當時另一位卓越的科學家Sir John Eccles則重新闡釋Henry Dale的概念為單一神經元只會釋放一種神經傳導物。從那之後「一神經元，一神經傳導物(one neuron, one transmitter)」的概念就被廣為接受。
Neuroscientists now know, however, that it is common for neurons to release a classical transmitter with another type of messenger, such as a gas (nitric oxide, for instance) or a neuropeptide (a small protein that can act as a transmitter). With the aid of new techniques for manipulating and imaging neurons, researchers have found that a number of neurons communicate using more than one classical neurotransmitter. Indeed, some of our auditory neurons simultaneously release three different classical transmitters during a brief period in development.
然而，現在神經科學家知道，神經元其實普遍在釋放一種古典的神經傳導物之外，還會伴隨釋放其他的傳訊分子，例如一氧化氮(nitric oxide)或神經肽類(neuropeptide)。由於有了新的操作技術以及顯影技術，研究人員發現許多神經元甚至能使用不只一種古典神經傳導物。例如，有些聽覺神經元在短暫的發育過程中能同時釋放三種古典神經傳導物。
So we see that “one neuron, one transmitter” is a bit too simplistic. But what about the original principle put forth by Dale that all axonal branches of a neuron release the same transmitter? There now appear to be at least a few exceptions to this principle. Motor neurons, which are important for voluntary muscle movements, have long been known to release acetylcholine onto both muscle cells in the body and neurons in the spinal cord. Recent studies show, however, that motor neurons also release a second transmitter, glutamate. Remarkably, they appear to release glutamate only onto neurons in the spinal cord and not onto muscle cells—in other words, certain branches of a single neuron release glutamate, and others do not.
所以我們知道「一神經元，一神經傳導物」的假說是太過簡化了。那麼最初Dale提出的假說「所有的軸突分枝都釋放相同的神經傳導物」呢？至少我們發現有一些例外。運動神經元曾被認為只釋放乙醯膽鹼(acetylcholine)到脊髓及肌肉細胞上，然而，運動神經元其實還會釋放麩胺酸(glutamate)。值得注意的是，運動神經元似乎只會釋放麩胺酸到脊髓而不會釋放到肌肉細胞上，這代表說單一運動神經元只有部分的軸突會釋放麩胺酸，而其他不會。
A next step in neurotransmitter research will be to understand how the release of more than one messenger ¬affects the function of the neural cir¬cuit and the organism as a whole. The fundamental question you ask has led to nearly a century of fascinating research, and it will continue to be an active and exciting area of investigation.
下一步的神經傳導物研究將能明白釋放多種神經傳導物的能力將如何影響神經迴路(neural circuit)的功能以及影響整個生物體。
[ 本帖最後由 abc2108612 於 2011-8-30 23:04 編輯 ]
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