International Research Compendium - Drug Free Australia

Drugs work in the brain because they have a similar size and shape as natural
neurotransmitters and interact with receptors and other components of the synapse.
Drugs masquerade as neurotransmitters and therefore interfere with normal synaptic
transmission by introducing false messages or by changing the strength of real ones.
Disrupting the transmission of information at the synapse is the basic mechanism by
which drugs change behaviour. Drugs lock into receptors and start an unnatural
chain reaction of electrical charges, causing neurons to release large amounts of
their own neurotransmitter.
Every type of drug has its own individual mechanism for changing how the brain
functions.
Regardless of which drug a person is addicted to, many of the effects it has on the
brain are similar. Since there is much more dopamine released, there is increased
activation of dopamine receptors. This causes increased production of Cyclic AMP (
Adenosine monophosphate ) inside the post-synaptic cell which alters the normal
activity of the neuron. Cyclic AMP is an intracellular second messenger that can
initiate a wide variety of changes in the postsynaptic cell. Effects of an upregulated
cyclic AMP system have been demonstrated in many of the relevant brain regions
regarding substance use, such as the Nuc. Accumbens and the VTA. Through
upregulation of cyclic AMP, drugs induce a variety of molecular changes in neurons,
thereby remodelling and restructuring neurons. Synaptic plasticity ( the
reorganisation of neural circuitry ) by psychoactive substances can occur via changes
in neurotransmitter release, the status of the neurotransmitter receptors, receptormediated
signalling or the number of ion channels regulating neuronal excitability.
Repeated stimulation of receptors by drugs can lead to alterations in receptor number
and function. Many of the synaptic changes are thought to be mediated by processes
similar to those for learning and memory. There are both presynaptic changes (
increased dopamine release ) and postsynaptic changes ( changes in receptor
sensitivity ).
The result of this process is that drugs change the way the brain works, and that
changes how people perceive the world, how they feel about themselves and their
world, and how they behave. These changes have a huge influence on all aspects of
a person’s behaviour. A drug can become the single most powerful motivator in a
drug abuser’s existence. This does not mean that the addict has no ability to make
choices. But it does mean that the ability to make choices is altered.
Drugs teach people to take more drugs
The development of drug addiction can be seen as part of a learning process, in the
sense that enduring changes in behaviour result from interactions with drugs and
drug-related environments. The repetitive, profound stimulation of dopamine
transmission induced by drugs in the Nuc. Accumbens abnormally strengthens drugtaking
behaviour. The powerful memory of early drug experiences is one of the things
that drives users to keep taking drugs.
The huge release of dopamine in response to a reward leads to a strengthening of
the synaptic connections in neural pathways that led to the behaviour that was
associated with the reward.
Structural changes in the synapse of connecting neurons enable people to learn and
retain what they have experienced by using drugs. This reinforces the behaviours
that led to the occurrence of that reward. And the brain becomes more sensitive to
13