Genetic factors of mental disorders
Understanding the processes taking place in the brain is impossible without considering heredity. Scientific data confirm that the risk of developing many severe diseases is directly related to genetics, regardless of upbringing and environmental conditions.
- Twin studies: The degree of trait overlap (the so-called concordance) in monoidentical (monozygotic) twins is many times higher than that in dizygotic twins. This pattern has been statistically proven for schizophrenia, endogenous depression, childhood autism, idiopathic epilepsy, Alzheimer's disease, and alcoholism.
- Adoption studies: The probability of developing alcoholism or schizophrenia in a child remains consistently high if their biological parents suffered from these pathologies. At the same time, the health status of adoptive parents (even completely healthy ones) does not reduce the genetically determined risk.
Dopaminergic system
Among all neurotransmitters affecting the systema limbicum, catecholamines have been studied in the most detail. A central role here is played by dopamine, which is synthesized from the amino acid tyrosine and serves as the basis for the subsequent formation of norepinephrine.
Features of the dopamine network:
- Localization: Dopamine-producing neurons are compactly grouped in subcortical nuclei (substantia nigra), the hypothalamus, and the striatum. From there, axons project into the limbic system, frontal cortex, neostriatum, and pituitary gland.
- Functions: The neurotransmitter has an excitatory effect on the nervous system. It controls muscle tone and behavioral reactions, increases blood pressure, and suppresses prolactin synthesis. Together with endorphins, dopamine ensures the functioning of the "pleasure centers".
- Pathologies: An excess of dopaminergic activity causes positive symptoms of schizophrenia (delusions, mania, hallucinations). Such excessive excitation is triggered by stimulant drugs. Depletion of dopamine stores leads to irresistible craving in addiction, while abrupt withdrawal of psychoactive substances causes a compensatory release of the neurotransmitter and the development of acute psychosis (delirium).
- Therapy: The treatment of schizophrenia is based on the use of antipsychotics (neuroleptics), which block dopamine receptors. A side consequence of such blockade is drug-induced parkinsonism, accompanied by tremor and muscle rigidity.
Norepinephrine and serotonin
Norepinephrine is formed from dopamine and acts as the primary transmitter of the sympathetic nervous system. Its centers are located in the brainstem (reticular formation, locus coeruleus), from which projections go to the cortex and limbic structures. It excites the hypothalamus, inhibits the cortex, controls the sleep-wake cycles, and shapes feelings of anxiety, fear, and pain.
Serotonin (5-hydroxytryptamine) is localized in the raphe nuclei of the pons (within the CNS), while in the periphery it is abundantly produced by chromaffin cells of the intestine. Its area of responsibility includes the formation of holistic images, eating behavior, and sleep. Hallucinogenic substances (e.g., LSD or psilocybin) can cause perceptual distortions precisely due to their structural similarity to serotonin.
To assess serotonin metabolism, the level of 5-hydroxyindoleacetic acid (5-HIAA) in urine is measured. Its extreme deficiency indicates severe depression with suicidal risk, while an excess indicates the presence of carcinoid tumors or the consequences of taking phenothiazine neuroleptics.
Monoamine hypothesis of depression
The link between mood and monoamine levels in synapses is considered proven thanks to pharmacological practice.
- Treatment: Antidepressants work by inhibiting the reuptake of norepinephrine and serotonin, or by blocking the MAO enzyme, preventing the oxidation of neurotransmitters.
- Provocation: Drugs that block the receptors of these substances (e.g., reserpine) can artificially trigger the onset of clinical depression.
Role of histamine
Histamine is an excitatory neurotransmitter closely associated with the development of allergic reactions. Its neuronal clusters are also concentrated in the hypothalamus. The axons of the histaminergic system project into many parts of the brain, including the cortex, thalamus, and limbic complex.
Briefly: answers to topical questions
What functions does dopamine perform in the central nervous system?
In the central nervous system, dopamine has a predominantly excitatory effect and performs a number of crucial regulatory functions.
- Regulation of movement — ensures muscle tone and motor activity.
- Regulation of mental activity — controls the emotional state, behavior, mood, motivation, and cognitive activity.
- Ensuring the functioning of the "pleasure centers" — functions in close interaction with the endorphin system.
- Endocrine function — suppresses prolactin synthesis in the pituitary gland.
Dopamine also helps increase blood pressure.
What functions does serotonin regulate in the human body?
Serotonin performs many functions, regulating both mental and physiological processes in the body.
- Regulation of psyche and behavior — participates in the formation of emotional reactions, mood, eating behavior, and holistic perception of images.
- Regulation of biorhythms — controls the sleep-wake cycle, serving as a precursor to melatonin.
- Sensory and autonomic regulation — affects pain perception and thermoregulation.
- Peripheral effects — stimulates intestinal peristalsis and exerts a vasoconstrictive effect during platelet aggregation.
What anatomical structures make up the limbic system?
The limbic system includes ancient brain formations that form the structural basis of emotions.
- Hypothalamus (Hypothalamus) — the central link of autonomic and endocrine regulation.
- Septum (Septum) — the area associated with pleasure centers.
- Amygdala (Corpus amygdaloideum) — is responsible for generating fear and aggression.
- Hippocampus (Hippocampus) — ensures memory, spatial orientation, and the emotional coloring of memory.
- Cingulate gyrus (Gyrus cinguli) — regulates behavior and autonomic functions.
The limbic system also includes the fornix, mamillary bodies, and the anterior nucleus of the thalamus, which form the closed Papez circuit.
Which enzymes carry out the catabolism of catecholamines and serotonin?
The catabolism of catecholamines and serotonin involves monoamine oxidase and, for catecholamines, catechol-O-methyltransferase.
- Monoamine oxidase (MAO) is involved in the inactivation of dopamine and norepinephrine, and also breaks down serotonin into 5-hydroxyindoleacetic acid.
- Catechol-O-methyltransferase (COMT) is involved in the inactivation of catecholamines, in particular norepinephrine.
End products of degradation: for dopamine — homovanillic acid, for norepinephrine — vanillylmandelic acid and 4-methoxy-4-hydroxyphenylglycol, for serotonin — 5-hydroxyindoleacetic acid.
What else to study on this topic
- Mechanisms of neurotransmitter catabolism by the enzyme monoamine oxidase
- Specifics of drug-induced parkinsonism compared to idiopathic Parkinson's disease
- Features of the action of phenothiazine neuroleptics
- The formation of withdrawal syndrome at the biochemical level
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