Key Components and the Reward Phenomenon
The development of addiction is a staged process consisting of four key components:
- Pathological craving for repeated PAS intake.
- Development of psychological dependence.
- Development of tolerance.
- Development of physical dependence.
At the core of the pathogenesis is the reward phenomenon. PAS intake triggers a massive release of neurotransmitters from storage vesicles. Anatomically, this process is mediated through the structures of the reward system: the limbic system and the brainstem (specifically, the locus ceruleus located on the floor of the fourth ventricle).
Initially, neurotransmitter release leads to pronounced positive emotions, euphoria, and increased productivity. However, this effect is transient: catecholamines are rapidly metabolized, their reserves become depleted, and a reward deficit ensues (fatigue, psycho-emotional discomfort, depressed mood). A pathological system forms, driven by the goal of obtaining a new dose of the PAS to restore a state of comfort.
Mechanisms of Tolerance Development
Tolerance manifests as a reduction or complete elimination of the effects produced by a standard dose of a PAS, forcing the patient to constantly increase the amount of the substance consumed. The triggering factor is repeated PAS intake. This process occurs via two main pathways:
- Metabolic pathway (accelerated degradation). The body activates cellular microsomal enzyme systems and cytosolic dehydrogenases. As a result, the destruction and inactivation of the psychoactive substance are intensified.
- Membrane-receptor pathway (decreased sensitivity). Excess cholesterol and saturated fatty acids accumulate within the phospholipids of neuronal cell membranes. Membranes become more viscous and lose their fluidity. Consequently, receptors become fixed within the thickness of the plasmalemma, their mobility decreases, and they become less accessible to neurotransmitters of the reward system.
Psychological and Physical Dependence
Psychological dependence is based on discomfort (depression, profound anguish, anxiety) that occurs when PAS intake ceases. The substance becomes a necessary condition for achieving satisfaction and mental uplift.
To compensate for the constant massive release and enzymatic degradation of neurotransmitters, the reward system undergoes remodeling: the synthesis of dopamine and norepinephrine is accelerated many times over, and catecholamine turnover speeds up.
Physical dependence is a state in which withdrawal of the PAS causes not only psychological discomfort but also profound acute disruptions in central nervous system (CNS) function and internal organs. At this stage, periodic or continuous administration of the substance is required by the body to alleviate severe physical disorders.
Withdrawal Syndrome (Abstinence Syndrome)
Withdrawal syndrome develops upon cessation of PAS use against the backdrop of already established physical dependence. Its pathogenesis involves several mechanisms:
- Catecholamine accumulation. Upon abrupt cessation of the PAS, the rate of neurotransmitter synthesis remains high by inertia, while their utilization drops (due to the lack of a stimulus for release). An excess of dopamine and other catecholamines accumulates in brain tissue.
- Membrane hypersensitivity. During intoxication, membrane viscosity was optimal for neurons (adaptation). Upon PAS withdrawal, receptors "float up" to the surface of the plasmalemma. Their accessibility increases sharply, leading to generalized CNS hypersensitivity.
- Neurotransmitter system imbalance (especially in chronic alcoholism). The activity of the excitatory glutamatergic system increases, while the inhibitory GABAergic system is critically suppressed.
Clinical presentation includes psychiatric changes (anxiety, irritability, anguish), pain syndromes (muscle aches, leg cramps, gastrointestinal pain), dyspepsia (nausea, vomiting, diarrhea), and autonomic reactions (blood pressure fluctuations, tachycardia, sweating, insomnia).