Addiction: The Biological Mechanisms of Addiction

Disruptions of the Neural Networks

Research has demonstrated that changes made to neural networks can result in abnormal and even addictive behavior. For example, in some parts of the CNS, post-synaptic receptors can be occupied by the neurotransmitter dopamine (DA). If the drug Haldol is administered, it will occupy the same receptors and not allow DA to bind. This blocking inhibits the overactive neurotransmission that is associated with schizophrenia and helps to eliminate large mood swings commonly seen amongst schizophrenia patients. Cocaine, on the other hand, prevents the degradation of the neurotransmitter in the synaptic junction. This will result in an overabundance of neurotransmitter in the junction available for binding to the post-synaptic membrane. Overly saturated receptors lead to over-active transmission of the electrical impulse and result in an increased stated of arousal.

Disruptions of the pre-synaptic terminal

Other areas where neurotransmission can be disrupted are located within the pre- synaptic terminal itself. Inside the terminal are monoamine oxidases (MOA), enzymes that degrade neurotransmitters such as dopamine and norepinephrine. In some individuals, there is too much MOA, which results in a lowered level of the neurotransmitter and a subsequent state of depression. Giving these patients MOA inhibitors will transiently resolve the depressive mood.

Disruption of the cAMP system

Disruption of the cAMP system operates in a different fashion and demonstrates the neurochemical mechanism for tolerance. In its homeostatic state, the brain attempts to counter the effects of activities that result in a change of neurotransmission. Thus, an initial increase in cAMP will be countered by a decrease in adenylate cyclase. As adenylate cyclase levels are down regulated, less cAMP is produced, neurotransmission is slowed, and a change in mood results. When this occurs, the desired state of arousal or mood can only be achieved by increased activity or substance ingestion. This phenomenon, known as tolerance, is an important component of addiction and will be discussed later. The cAMP system also achieves a link between biochemistry and withdrawal symptoms. Removal of the activity or drug results in a massive decreased production of cAMP that will lead to symptoms of withdrawal, including anxiety and lethargy.

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