Возможные механизмы антидепрессивного действия антипсихотиков второго поколения

Although the exact mechanism of SGAs for MDD has not yet been clearly elucidated, several plausible underlying mechanisms are listed as follows: modulation of crucial neurotransmitter receptors and transporters such as dopamine, serotonin and noreinephrine resulting in net effect of enhancement of such neurotransmitters' transmission, effects on sleep, alteration of various hormones (ACTH, sex hormones, etc.), modification of immune functions including modulation of inflammation process (cytokines, etc.), antioxidation process and modulation of neurotrophic factors (BDNF, etc).[13]

Specifically, the main pharmacological rationale of SGAs as an antidepressant augmentation would be based on their effects on monoamine transporters or receptors of crucial neurotransmitters such as serotonin, norepinephrine and dopamine, which are also the main target of contemporary antidepressants. The partial agonism at D2 and/or D3 receptors may increase dopamine neurotransmission at the prefrontal cortex. The increase in the dopamine concentration in the prefrontal cortex may be also indirectly related to the antidepressive effect of 5-HT1A receptor agonist.[14,15] The antidepressant effect may also be mediated by 5-HT1A partial agonism and/or antagonism at 5-HT2A receptors.[16–18] Although, still controversial, the antidepressant effect of 5-HT1A receptor agonists may be predominantly mediated by postsynaptic 5-HT1A receptors, while the anxiolytic effect would be mainly associated with presynptic 5-HT1A receptors.[19] The antagonism of the 5-HT2C receptors has been also found to be involved in increased dopamine and norepinephrine transmission.[20] It is also well known that high affinity at the α2-adrenergic receptor may enhance the release of norepinephrine.[21] Unlike any other SGAs, ziprasidone was reported to block synaptic serotonin, norepinephrine and dopamine reuptake in vitro.[22,23] Evidence indicates that both 5-HT6 agonists and antagonists may evoke identical responses in animal models of MDD, although the possible mechanisms of these effects seem to be diverse and are not clearly understood. The augmented effects were notable by combining antidepressants with a selective 5-HT6 receptor antagonist.[24] There is also a considerable amount of evidence supporting a role for the 5-HT7 receptor in MDD. The blockade of the 5-HT7 receptor led to antidepressant-like effects in animal models of MDD. It should be also worthy to mention that augmentation of 5-HT7 receptor antagonists with antidepressants was remarkable in animal models of MDD.[25]

Another mechanism involving in the action of SGAs should be the alteration of the glutamate receptor activity, and thus restoring normal glutamatergic neurotransmission and reducing the chances of excitotoxicity.[26] Some SGA treatment may also cause a decrease in plasma adrenocorticotropic hormone concentration and a normalization of HPA-axis dynamics.[27] An impaired neuroprotection has also been implicated in the pathophysiology of MDD.[28,29] Interestingly, activation of the 5-HT1A receptors was shown to be neuroprotective against various brain insults such as N-methyl-daspartic acid.[30] Some SGAs have also demonstrated such neuroprotective effects indicating a potential role in the protection against excitotoxicity in vivo.[30]

Overall 5-HT2A antagonism should be a commonly shared biological relevance for most of the SGAs as a potential mechanism of their antidepressant effect. Interactive effects with the dopaminergic system may be more distinct with the action mechanism of amisulpride and aripiprazole, while norepinephrine- and/or serotonin-reuptake inhibition should be the unique case with quetiapine or ziprasidone.[31] Each antipsychotic has a distinct profile of affinities towards different neurotransmitter receptors, which should be associated mainly with mediation of antidepressant-like effects.

Second-generation Antipsychotics in the Treatment of Major Depressive Disorder

Brain Dopamine–Serotonin Vesicular Transport Disease and Its Treatment

Known disorders of biogenic amine neuromediators (dopamine, norepinephrine, epinephrine, and serotonin) involve defects in nine enzymes1-9 and one transporter.10 Affected persons present in early childhood with symptoms referable to the affected neurotransmitter, and the disorders are diagnosed by measurement of neurotransmitter breakdown products in the cerebrospinal fluid (CSF). A deficiency in dopamine results in movement disorder; deficient norepinephrine or epinephrine causes autonomic dysfunction; and serotonin deficiency leads to sleep and psychiatric disturbances.2,3,6
We describe members of a family with symptoms of deficiencies in dopamine (dystonia, parkinsonism, and oculogyric crises), serotonin (sleep and mood disturbance), and epinephrine and norepinephrine (diaphoresis, temperature instability, ptosis, and postural hypotension), with no demonstrable deficiency of neurotransmitters in the CSF. Genome investigation revealed a mutation in the gene encoding VMAT2 that compromises transport of biogenic amines into synaptic vesicles, resulting in impairment of their synaptic transmission without detectable reductions in their amounts.

 Brain Dopamine–Serotonin Vesicular Transport Disease and Its Treatment

Агрессивность может быть связана со снижением функции дофаминергической системы

The neurobiology of aggression is not well understood, but scientists are aware of a relationship between the neurotransmitter serotonin and certain aggressive behaviors. The objective of this study was to explore whether higher levels of another brain chemical called dopamine, involved in pleasure and reward, increased aggressive response in its subjects. To scientists' surprise, it was not as they first theorized.

"The results of this study were astonishingly opposite of what was previously hypothesized," says Ingo Vernaleken, M.D., lead author of the study and research scientist for the department of psychiatry at RWTH Aachen University in Aachen, Germany. "Subjects with more functional dopaminergic reward-systems were not more aggressive in competitive situations and could concentrate even more on the game. Subjects with lower dopaminergic capacity were more likely to be distracted by the cheating behavior."

Molecular Imaging Finds Link Between Low Dopamine Levels and Aggression

Взаимодействие рецепторов серотонина и глутамата как возможный механизм психоза

Serotonin (5HT) and glutamate are two neurotransmitters. Up until now, it was thought that they acted independently. A given neuron might have receptors for both serotonin and glutamate, but they didn't interact: serotonin would never affect the glutamate receptors, and vice versa.
The new research overturns that view. Authors Miguel Fribourg and colleagues ofMount Sinai School of Medicine show, in a series of elegant experiments in mice, that different receptors can cluster together, forming a complex. The two receptors, serotonin's 5HT2A and glutamate's mGluR2, can talk to each other.

A Psychedelic Tale of Two Neurotransmitters