The mechanism of the appearance of "voices" in patients with schizophrenia has been established
Says dopamine
Artem Astashenkov, "Russian Planet"American scientists have established the cause of auditory hallucinations in patients suffering from schizophrenia.
The disruption of neural connections between two specific brain regions caused by an excess of dopamine leads to the appearance of "voices," according to a study published on June 6 in the journal Science – Chun et al., Specific disruption of thalamic inputs to the auditory cortex in schizophrenia models. (St. Jude Children's Research Hospital Brain circuit problem press release likely sets stage for the "voices" that are a symptom of schizophrenia published on AlphaGalileo – VM.)
Doctors have long known that schizophrenia is accompanied by an unnatural level of the neurotransmitter dopamine (dopamine) in the brain. For decades, drugs that bind the dopamine receptor D2 (Drd2) have been used to suppress the symptoms of the disease, which reduces the production of the corresponding protein. However, the nature of the relationship between the level of substance and mental deviation remained unknown.
Another factor empirically associated with schizophrenia is the Di Giorgi syndrome – deletion (deletion) of a certain site on one of the pairs of the 22nd chromosome. In the presence of such a deviation, the patient has only one copy of about 25 genes instead of two. Among them, for example, Dgcr8, the absence of which, as the same group of scientists found out earlier, leads to memory and learning disabilities. Statistically, about 30% of people with 22q11 deletion suffer from schizophrenia.
For their experiment, a group of scientists from St. Jude Children's Research Hospital (Memphis, Tennessee) used genetically modified mice that had simulated Di Giorgi syndrome. The object of the study was the area of the cerebral cortex responsible for the redistribution of signals from the sensory organs – the thalamus. In his auditory zone, as experts found out, the impulses in sick mice were much weaker than in healthy ones. The study of the brains of animals with damaged chromosomes showed that the levels of dopamine receptor D2 were elevated in the auditory part of the thalamus, and nowhere else. Comparison of these results with tissue samples of 26 people – both healthy and schizophrenic – confirmed the scientists' finding: dopamine was definitely "involved" in slowing down sound signals.
The last piece of the puzzle fell into place when scientists tried to "treat" mice from schizophrenia with standard means – haloperidol and clozapine, which block the production of dopamine. In animals that received the drugs, the intensity of signals in the auditory area of the thalamus was gradually restored, and in other areas of the brain did not change.
The fact that sick mice (like humans) "hear voices", scientists blame the Dgcr8 gene, which this research group has encountered before. They found that animals deprived of this gene react to loud sounds exactly like schizophrenics. A person reacts to a sharp loud sound much less sharply if he has already heard another unexpected sound a few tenths of a second before. This is called "pre-pulse inhibition". The reaction of a healthy individual to the second sound is suppressed by 65%, and only if the sounds are separated for at least 0.5 seconds, the second causes a stronger response than the first.
The situation is different for people with different mental disabilities. In the case of schizophrenia, for example, suppression does not occur. This is what scientists have noticed in sick mice that do not have the Dgcr8 gene. The animals that received haloperidol reacted to the test with a preliminary impulse in the same way as healthy ones.
The discovery of American scientists opens the way to the development of more "targeted" drugs to suppress the symptoms of schizophrenia and expands medical understanding of the problems of early brain development.
Portal "Eternal youth" http://vechnayamolodost.ru06.06.2014