Archive for October, 2012

What happens to your brain if you keep taking drugs?

Just as we turn down the volume on a radio that is too loud, the brain adjusts to the overwhelming surges in dopamine (and other neurotransmitters) by producing less dopamine or by reducing the number of receptors that can receive signals.

As a result, dopamine’s impact on the reward circuit of a drug abuser’s brain can become abnormally low, and the ability to experience any pleasure is reduced. This is why the abuser eventually feels flat, lifeless, and depressed, and is unable to enjoy things that previously brought them pleasure. Now, they need to take drugs just to try and bring their dopamine function back up to normal. And, they must take larger amounts of the drug than they first did to create the dopamine high – an effect known as tolerance.

 

Decreased Dopamine Transporters in a Methamphetamine Abuser

brain scan

Methamphetamine abusers have significant reductions in dopamine transporters.
Source: Am J Psychiatry 158:377–382, 2001.

 

We know that the same sort of mechanisms involved in the development of tolerance can eventually lead to profound changes in neurons and brain circuits, with the potential to severely compromise the long-term health of the brain. For example, glutamate is another neurotransmitter that influences the reward circuit and the ability to learn.

When the optimal concentration of glutamate is altered by drug abuse, the brain attempts to compensate for this change, which can cause impairment in cognitive function. Similarly, long-term drug abuse can trigger adaptations in habit or no conscious memory systems. Conditioning is one example of this type of learning, whereby environmental cues become associated with the drug experience and can trigger uncontrollable cravings if the individual is later exposed to these cues, even without the drug itself being available. This learned “reflex” is extremely robust and can emerge even after many years of abstinence

Chronic exposure to drugs of abuse disrupts the way critical brain structures interact to control and inhibit behaviours related to drug abuse. Just as continued abuse may lead to tolerance or the need for higher drug dosages to produce an effect, it may also lead to addiction, which can drive an abuser to seek out and take drugs compulsively. Drug addiction erodes a person’s self-control and ability to make sound decisions, while sending intense impulses to take drugs.

 

How does the brain communicate?

The brain is a communications centre consisting of billions of neurons, or nerve cells. Networks of neurons pass messages back and forth to different structures within the brain, the spinal column, and the peripheral nervous system. These nerve networks coordinate and regulate everything we feel, think, and do.

  • Neuron to Neuron
    Each nerve cell in the brain sends and receives messages in the form of electrical impulses. Once a cell receives and processes a message, it sends it on to other neurons.
  • Neurotransmitters – The Brain’s Chemical Messengers
    The messages are carried between neurons by chemicals called neurotransmitters. (They transmit messages between neurons.)
  • Receptors – The Brain’s Chemical Receivers
    The neurotransmitter attaches to a specialized site on the receiving cell called a receptor. A neurotransmitter and its receptor operate like a “key and lock,” an exquisitely specific mechanism that ensures that each receptor will forward the appropriate message only after interacting with the right kind of neurotransmitter.
  • Transporters – The Brain’s Chemical Recyclers
    Located on the cell that releases the neurotransmitter, transporters recycle these neurotransmitters (i.e., bringing them back into the cell that released them), thereby shutting off the signal between neurons.

To send a message a brain cell releases a chemical (neurotransmitter) into the space separating two cells called the synapse. The neurotransmitter crosses the synapse and attaches to proteins (receptors) on the receiving brain cell. This causes changes in the receiving brain cell and the message is delivered.

Most drugs of abuse target the brain’s reward system by flooding the circuit with dopamine.