Academic journal article International Public Health Journal

Understanding Substance Use Disorders

Academic journal article International Public Health Journal

Understanding Substance Use Disorders

Article excerpt


Substance use disorders are characterized by a chronic remitting and relapsing course. Symptoms of tolerance and withdrawal are characteristics of physical dependence, but maladaptive patterns of behavior are key to the diagnosis of substance use disorders. In the following text we will briefly review the neurobiology of addictive disorders and for the sake of simplicity, the above-mentioned terms will be used interchangeably. Psychoactive substances act on the neuronal structures and processes that are important for the regulation of healthy mood, behavior, and motivation. Most of the current understanding of this cause and effect is derived from animal models of addiction. These models have been particularly helpful to demystify mechanisms at the neuronal and synaptic level during the acute phase of drug intake. With advancement in research techniques, animal models of chronic drug preference, self-administration, reward, cravings, tolerance development, and withdrawal are being developed in order to better understand the neuro-adaptive mechanisms underlying long-term use. Use of genetic variants and characterization of receptor subtypes and interacting neuronal circuits have advanced our understanding of how addictive drugs work in the brain. More recently, the use of positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have provided critical insights into this highly complex neuro-cognitive loop. Progress in neurobiology is so rapid that we can only hope to capture a snapshot of today's view as what we know keeps changing.

General concepts

In the majority of cases, substance use starts either as a recreational activity or as a means to gain some perceived benefits from a particular drug (e.g., pain relief from prescription opioids, control of anxiety, anger, depression, or increasing energy or attention). With repeated intake, a maladaptive pattern of use and loss of control of consumption accompanies the transition to drug dependence. Seeking faster routes of administration, escalating doses, evolution of purpose for taking the drug, repetitive patterns of use, shifting social support network to incorporate mostly other users, ease of access to drugs, abandoning healthy supports and activities, emotional stress, disregard of danger warnings, and lack of enforcement of safety procedures all play roles in facilitating the progression to harmful addictive use. At this stage, the individual's use becomes more habitual and continues despite ongoing adverse effects and deterioration in psychosocial functioning. From a clinical point of view, this use results in the emergence of complex behavioral problems that probably are a result of substance induced neurochemical changes in the nervous system.

During the early days of addiction research, the brain reward system was considered the final common pathway in the addiction process. Recent research, however, has shown that the addiction models are more complex than can be explained by the reward model alone. In addition, it is important to understand that effects of drugs on the reward system continue to play an important role in the overall understanding of the neurobiology of addiction (1). Numerous brain structures are involved in the circuitry of learning, motivation, reward, and pleasure. The caudate, putamen, globus pallidus, and amygdala constitute the basal ganglia. The caudate and putamen together are called the striatum. The nucleus accumbens (NAc) is associated with reward, motivation, and learning. The hippocampus in the limbic system has widely dispersed neuronal connections and plays a role in the development of dependence. Other areas of interest include: orbitofrontal cortex (inhibitory control), prefrontal cortex (executive control), and hypothalamic-pituitary-adrenal axis (associated with stress).

Given the importance of these areas in the regulation of behavior and emotion, it is no surprise that these structures have been the focus of intense scrutiny in substance abuse research. …

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