1. The brain is a structure that controls many different functions; areas within the brain are highly specialized to control specific functions, but they are also interconnected.

2. Neurons send information to each other using both electrical and chemical signals. Electrical information moves along a neuron, and chemical information moves between neurons. When they work together as a unit, the neurons control the function of a specific brain area.

3. The communication between neurons can be disrupted by drugs; this happens specifically at the synapse, the most important control point in the process of communication.

4. Regardless of their method of intake, drugs of abuse, such as nicotine, cocaine and marijuana, reach the brain through the bloodstream. When drugs are smoked they reach the brain as fast as if they were injected, and even faster than if snorted or taken by mouth. The faster a drug reaches the brain, the more likely it will be abused.

5. Drugs interact with neurons at the synapse. Their targets can be receptors (e.g. for nicotine and marijuana) or uptake pumps (e.g. for cocaine).

6. By acting at the synapse, drugs change the way the brain functions and can affect behavior, thinking and learning, movement and sensations. Sometimes this is beneficial, as in the treatment of a disease, and sometimes this is detrimental, especially when drugs are abused.

 

 

Dopamine is a neurotransmitter. The surge of dopamine in a drug addict's brain is what triggers a cocaine high. Where another transmitter called serotonin is associated with feelings of sadness, dopamine is associated with pleasure and elation. Dopamine can be elevated by potent pleasures that come from drugs, but also to a lesser degree by a word of praise or winning a tennis match etc. At a purely chemical level, every experience that human beings find enjoyable - whether listening to music or savoring a chocolate - amounts to little more than an explosion of dopamine in a certain area in the brain. Addicts therefore do not crave heroin or cocaine or alcohol or nicotine per se, but actually want the rush of dopamine that these drugs produce. These drugs, so to say, hijack the natural brain reward systems that control behavior.

1.  Which neurotransmitter is associated with the feelings of pleasure or elation?
2.  Which neurotransmitter is associated with feelings or sadness?


That is not to say that dopamine is the only chemical involved. The brain is more complex than that. Drugs modulate the activity of a variety of brain chemicals, each which intersects with many others. Among some 50 neurotransmitters discovered to date, a good half-dozen are known to play a role in addiction. Neurotransmitters underlie every thought and emotion, memory and learning. Nevertheless, it seems as if dopamine may be the common end point of all those pathways.

3.  ~ how many neurotransmitters do we know exist?
4.  Of the known transmitters, ~ how many have a role in addiction?

Once the dopamine has locked into the receptors and transferred the impulse/signal, it will either be reabsorbed into the nerve ending from which it came, or else be destroyed by an enzyme. Amphetamines stimulate dopamine-producing cells to pump out more dopamine. Cocaine keeps the levels of dopamine high at the synapses, by preventing the re-absorption of dopamine back into the cells that produced it. Nicotine, heroin and alcohol trigger a complex chemical cascade that raises dopamine levels. Another unknown chemical in cigarette smoke may extend the activity of dopamine, by blocking a mopping up enzyme that would otherwise destroy it.
 
5.  What is the relationship between amphetamines and dopamine?
6.  What is the relationship between cocaine and dopamine?
7.  What is the relationship between nicotine, heroin and alcohol and dopamine?


Dopamine also appears to play a large role in causing the craving for drugs. The major drugs abused, whether depressants like heroin or stimulants like cocaine, mimic the structure of neurotransmitters. In this way, cocaine ties up to available binding sites on the molecules that transport dopamine through the brain. To produce any high at all, cocaine has to occupy at least 47% of these sites. The “best” results occur when it takes over 60% - 80% of the sites, effectively preventing the transporters from latching onto dopamine and removing it from the circulation.
 
8.  What minimum % of the binding sites has to be occupied by cocaine molecules to stimulate the feelings of a 'high' in a user?

So how does addiction come about? One explanation is that the addict's neurons, assaulted by abnormally high levels of dopamine, try to adapt to these high levels of dopamine and reduce the number of sites (receptors) to which dopamine can bind. So, in the absence of drugs, these nerve cells probably experience a shortage of dopamine. So while addicts start taking drugs to feel high, they end up taking them in order not to feel low. 
 
9.  Explain how addiction comes about.

Cocaine

Increases the amount of dopamine available to cells by blocking the mechanism that usually gets rid of excess dopamine. It also blocks re-uptake of noradrenaline and serotonin. The rise in these three neurotransmitters causes the feeling of euphoria (dopamine), confidence (serotonin) and energy (noradrenaline) associated with the drug. This drug became popular in the 70's and was often presented as a "non-addictive" substance. Countless stories of destroyed lives, especially in the entertainment world, soon became the norm, and the "non-addictive" drug was proven to be just the opposite.

10.  Is cocaine addictive?

Alcohol

Decreases neural activity through action on GABA (gamma amino butyric acid) neurons. Drugs that block the receptors in these cells reduce the pleasure of drinking and are effective in weaning addicts off alcohol. Alcoholism and probably all drug addiction is closely associated with genetic factors. Children of alcoholics, for example, are four times more likely than other people to become addicted, unrelated to environmental factors.

11.  What sort of drug is used to help wean addicts off alcohol?
12.  Is there a relationship between addiction and a person's genes?  Give an example that supports this.

Amphetamines

Releases dopamine and normal adrenaline. This creates energy but may also produce feelings of anxiety and agitation.

13.  What sensations does a person experience when using amphetamines?

Opioids

These fit into receptors that normally take the neurotransmitters endorphins and enkaphelins. This triggers the reward circuit that creates the dopamine rush. The disengagement from pain produced by these drugs is thought to be caused by the deactivation of an area in the cortex called the anterior cingulate gyrus, which concentrates attention on adverse internal stimuli. The withdrawal effects of opioids are associated with steep rise in stress hormones that activate the urge-making areas of the brain. These drugs are among the most dangerously addictive due to the painful withdrawal symptoms.

14.   What part of the brain is effected by the use of opioids?  How does this cause the highly addictive nature of these drugs?

Nicotine

Activates dopamine neurons by mimicking the effect of dopamine in binding to receptors in the cells' surface. Its initial effect is therefore similar to a dopamine rush. Nicotine quickly desensitizes the cells it works on so the initial effects are no longer felt. Nicotine also affects neurons that produce a neurotransmitter called acetylcholine. This is one of the chemicals involved in alertness and is known to boost memory.

Tranquilizers

Has the same effect as alcohol, decreasing neural activity through action on GABA (gamma amino butyric acid) neurons.