Book T of C
Chap T of C
Neurotransmitters and neurohormones are involved in everything we do. To study them, researchers manipulate their levels around the synapse. Researchers found many ways to alter levels of transmitters. Here is a sampling (that you do not have to memorize). Transmitters may...
—interfere with a neurotransmitter's synthesis; this lowers its levels.
—provide an artificial transmitter that has the same effect as a natural transmitter (this raises transmitter levels).
—stimulate synthesis of a "false transmitter" that competes with the real transmitter for places on the postsynaptic membrane (this reduces the effects of the real transmitter).
—block removal of the transmitter. Normally transmitter substances are recycled. This is called re—uptake of the transmitter. If the recycling operation is blocked, excess transmitter gathers in the area of the synapse (this raises transmitter levels).
—cut down on calcium around the synapse, which prevents release of the transmitter substance from the vesicles (this lowers transmitter levels).
—provide the re—uptake system with "dummy" neurotransmitters that don't work when released (this lowers transmitter levels).
What "two things" are the result of manipulating transmitter levels?
The result is always one of two things: increasing or decreasing the amount of active transmitter at a synapse.
Blocking or accumulation of transmitters may occur in roundabout ways. Consider the case of caffeine, the active ingredient in coffee. Caffeine has a molecular shape similar to adenosine, a transmitter. Caffeine is able to occupy receptor sites on the postsynaptic membrane where adenosine would normally go. When caffeine occupies the receptor sites, adenosine cannot exert its usual inhibitory action. Thus caffeine wakes us up by blocking a transmitter (adenosine) that normally makes us sleepy.
How does coffee achieve its effect? Why was the mouse "laid back"?
From an article in Science: "Laid back mouse: A mouse treated with an adenosine mimic has lost its 'get-up-and-go'."
If coffee achieves its stimulatory effect by blocking adenosine, you would expect an adenosine mimic, a chemical which has the same effect as adenosine, to make animals sluggish. This is what happens. For example, a mouse treated with an adenosine mimic-a chemical with the same effect as adenosine-would "lie around loose, relaxed, and splayed out, but wide awake and responsive to painful stimuli." A cup of coffee would put it right back on its feet (Caffeine's stimulatory effects explained, 1981).
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Copyright © 2007 Russ Dewey