What Are Serotonin Autoreceptors?

Serotonin is a naturally occurring chemical produced by the body, regulating sleep, depression and memory. Serotonin belongs to a class of chemicals called neurotransmitters, which send signals across the brain, including how to feel, when to remember and when you are tired. Autoreceptors regulate the amount of serotonin that is transmitted. To better understand the role of serotonin autoreceptors in brain functioning, think of the brain as a vast area of sky, with planes flying around in it.

Brain-Airport Analogy

• Neurons are like airports.

  Airports send planes with cargo across the sky. In the brain, neurons are like airports, planes are like neurotransmitters with serotonin cargo, and the sky is called the synaptic cleft. The pre-synaptic neuron is the originating airport. The post-synaptic neuron is the receiving airport.

Air Traffic Controllers

• Autoreceptors are like air traffic controllers. There are autoreceptors both at the pre-synaptic neuron (the originating airport) and at the post-synaptic neuron (receiving airport).

Flight Path

• Once the serotonin reaches the synaptic cleft, chemical signals (like radio signals) are sent to both the pre-synaptic neuron and the post-synaptic neuron. These signals tell the pre-synaptic neuron to stop sending serotonin when the post-synaptic neuron has enough. They also tell the post-synaptic neuron when it is time to receive the serotonin cargo. This is known as post-synaptic re-uptake. For a plane to travel efficiently, a carefully planned flight time is essential. The same principle applies to the flight of the serotonin neurotransmitters across the synaptic cleft. There is an optimal time the serotonin should remain in the cleft before being received by the post-synaptic neuron.

Flight Problems

• Disruption of the autoreceptors can result in serotonin neurotransmitter problems, much like plane crashes.

  As in airports, sometimes things do not always function well. Although the exact causes are unknown, there can be defects in the process at any or all levels. Any of these problems can result in too much or too little serotonin being sent across the synaptic cleft, or serotonin not remaining in the synaptic cleft for long enough, leading to depression, insomnia and memory problems. Problems could include not enough autoreceptors at either the pre-synaptic or post-synaptic sites (the airports) or the serotonin not reaching the post-synaptic autoreceptors (lost in flight, crashes, misrouting).

Antidepressants

• Depression is thought to be caused, in some cases, by the serotonin not remaining in the synaptic cleft long enough. In other words, it is received by the post-synaptic neurons (via re-uptake) too quickly. Some antidepressants, known as Selective Serotonin Re-uptake Inhibitors, work to block reabsorption (re-uptake) of the serotonin, so that it stays in the synaptic cleft longer.