Drug addiction is a chronic disease characterized by changes in the brain.
A network of neurons in the brain known as the _________
________ is responsible for
driving our feelings of motivation, reward and behaviour. Neurons, such as those that
comprise the reward pathway, communicate at the synapse using ___________________.
There is a genetic component to addiction. The adolescent brain is particularly susceptible to
developing a lifetime addiction.
Within seconds of entering the body, drugs cause dramatic changes to synapses in the brain.
By bypassing the five senses and directly activating the brain's reward circuitry fast and
hard, drugs can cause a jolt of intense pleasure.
Drugs of abuse affect the brain in such a dramatic way that the brain must try to adapt.
One way the brain compensates is to ___________ the number of
dopamine receptors at the synapse. As a result, after the user has "come down",
they will need more of the drug next time they want to get high. This response is commonly
referred to as _______________________ .
As the brain continues to adapt to the presence of the drug, regions outside of the reward
pathway are also affected. Brain regions responsible for judgment, learning and memory
begin to physically change or become "hard-wired."
Once this happens, drug-seeking behaviour becomes driven by habit, almost reflex. This is
how a drug user becomes transformed into a drug addict
The simplified mechanisms of drug action presented on the mouse party animation are just a
small part of the story. When drugs enter the body they elicit very complex effects in many
different regions of the brain. Often they interact with many different types of
neurotransmitters and may bind with a variety of receptor types in a variety of different
locations. For example, THC in marijuana can bind with cannabinoid receptors located on the
presynaptic and/or postsynaptic cell in a synapse.
The mouse party presentation primarily depicts how drugs interact with dopamine
neurotransmitters because the website focuses on the brain's reward pathway. Mouse Party
is designed to provide a small glimpse into the chemical interactions at the synaptic level
that cause the drug user to feel 'high'.
List the main role(s) for each neurotransmitter below:
Dopamine:

Serotonin:
GABA:
The red traffic light
Glutamate: The green traffic light
Nerve cells communicate with each other at a junction called a ____________. When
stimulated by an __________________, a neuron releases neurotransmitters into the
synapse. Receptors on the outside of the receiving cell (post synaptic cell) fit synaptic
neurotransmitters similar to a “lock and key”. Once neurotransmitters “lock” into the
appropriate receptor, a ______________________is released in the receiving cell. After
neurotransmitters have done their job, they are released from the receptors and sent back
through the cell through re-uptake transmitters. In the sending cell, neurotransmitters are
packaged in vesicles.
1. What structure is responsible for “recycling” neurotransmitters back into the axon
terminal once they have done their job?
2. How do the vesicles “know” when to move to the membrane to dump their contents into the
synapse?
3. How does the message continue past the post-synaptic membrane?
4. Diagram, label and describe the action of dopamine while communicating a pleasure or
reward message across the synapse.
 

Natural
Opiate
H
Gabba
Heroin – looks like
inhibitory
a natural opiate
neurotransmitter
Using the heroin mouse
animation together with
the symbols to the right –
draw illustrations () to
demonstrate what is going
on in the synapse
Before heroin enters the system, inhibitory
neurotransmitters (gabba) are active – one effect of this is that it stops dopamine from
being released further down the line.
The gabba binds to a gabba receptor to prevent neural firing – which stops the action
potential which then stops dopamine being released.

So, put another way, when natural opiates bind with opiate receptors the release of
inhibitory neuro-receptors (gabba) is shut down…………………………………………...this means dopamine
is released.
Heroin LOOKS like a natural opiate and binds to the gabba neuro-receptors, this means
dopamine is no longer inhibited so you end up with a dopamine flood. The reward pathway is
activated and the resulting experience is one of sedation and well-being.

Pain signals are reduced. The stress response is reduced and emotional attachment is also
reduced.