That electric feeling  pg. 2

Sweeping the synapse
The dopamine transporter, pictured here as a vacuum -like tube, sweeps dopamine back into the nerve cell after its job is done (top panel).  Drugs like Ritalin are thought to block the dopamine transporter, thereby increasing the supply of dopamine in the synapse (bottom panel).
Illustrations by Dominic Doyle
The first molecules we’ll meet are the neurotransmitters, which actually jump the gap. They include dopamine, norepinephrine and serotonin. After leaving their nerve cell, they attach to and activate receptors on the next cell in line, much like a key fits into a lock. Millions of locks must be opened in this way to send messages down their “signaling pathways.” The ultimate goal may be to bend an arm or trigger the recollection of a childhood memory.

When these signals go awry, the body cannot function properly. Depression has been linked to a lack of serotonin. A loss of dopamine-producing cells in the brain causes Parkinson’s disease, the inability to control voluntary muscle movement. Altered levels of norepinephrine can trigger heart disorders, depression and attention deficits.

These three neurotransmitters have been implicated in a wide range of other brain disorders, from ADHD to schizophrenia, and they represent just a fraction of the molecules known to carry or modify messages along the convoluted avenues of nerves between our ears.

But it gets even more complicated. Dopamine has five known receptors (some of which also can be activated by norepinephrine), while serotonin has at least a dozen. On top of that, one of the dopamine receptors, D4, exists in several genetically distinct forms, or variants. Your dopamine messaging system may function differently, and you may respond differently to drugs that affect it, depending on which genetic variant you inherit.

A clean sweep

The next molecule we’ll meet on our journey is the transporter, an important regulator of neurotransmitter function. The transporter acts like a molecular vacuum cleaner, sweeping neurotransmitter back into the nerve cell after the message has jumped the gap, so it will be ready for the next signal.

When the transporter is blocked, neurotransmitter builds up in the synapse. This can be a good thing, if you’re trying to treat depression. By blocking the serotonin transporter, drugs like Prozac increase the supply of serotonin at the synapse, and help elevate mood.

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