Changes In Behavior Can Be Caused By Changes In Serotonin Level

Alterations of the genes encoding the above mentioned proteins and receptors result in the changes of the levels of serotonin and cause various behavioral changes.

Defects of 5-HT 1A receptors lead to the increase in anxiety. The decrease of the level of serotonin generated by the action of monoaminooxidase A was associated with violent behavior and antisocial personality disorder. Increased level of serotonin in early life, associated with decreased activity of monoaminooxidase A, seems to be correlating with the higher risk of violent behavior and aggression in the adulthood.

Abnormalities in serotonin signalling are important in development of schizophrenia (this is so-called serotonin hypothesis of schizophrenia). Drugs that can block 5-HT 2A serotonin receptors are effective for schizophrenia.

Various compounds capable of binding to serotonin receptors induce a variety of behavioral responses. Many drugs are acting via serotonergic system. For instance, the 5-HT 2A receptors seem to be involved in the mechanism of LSD, one of the strongest hallucinogens known. LSD binding with this receptor is an initial event leading to general decrease in inhibitory action of serotonergic system. Certain similarities between the effects of LSD and mystical experience makes some authors to speculate that serotonergic system is also involved in our perception of religious experience.

Connections between serotonergic activity and suicidal behavior

Researchers argue that the suicidal behavior can be connected to other characteristics such as impulsiveness and aggression and some individuals are more vulnerable due to underlying genetic factors. Some scientists estimate that genetic factors play role in 30 – 50% of suicides.

Low serotonergic activity is associated with depressions and suicidal behavior. There are a number of genetic factors leading to decreased level of serotonergic activity in certain areas of the brain. They contribute to the development of various psychopathologies.

Correlation between suicide attempts and decreased level of serotonin in cerebrospinal fluid was reported for patients with major depressions.

Tryptophan hydroxylase is one of the enzymes involved in biosynthesis of serotonin. Several genetic alterations in its gene were reported to be associated with suicidal behavior.

Impulsive aggressive and sexual behavior was well documented in mice lacking 5-HA 1B receptor gene which is similar to the human version. One common human version of this receptor seems to be associated with a history of suicide attempts. The results of these studies are not conclusive though.

Several studies report the connection between suicidal behavior and the elevated level of 5-HT 2A receptor in prefrontal cortex.

We don’t have genes for suicide but some genes are associated with predisposition to depressive and suicidal behavior

There is no single “suicide gene” in human genome, but some genetic mutations and alterations in the genes involved in regulation of serotonergic system certainly create conditions for higher likelihood of deep depressions and suicides. Suicidal behavior, like most of other psychopathological disorders, involves complex gene interaction and can’t be explained by only one single factor. The studies provide clear evidences that suicidal tendencies can be inherited by children from parents, and individuals that are genetically prone would have higher probability of committing suicide if they are faced with adverse life events or suffer from psychopathologies.

Serotonergic system doesn’t seem to have a direct control of anything critical but it participates in the vast variety of behavioral responses and modulates them. As a result, its involvements can be seen in a significant number of complex diseases and conditions such as schizophrenia and depression. The complexity of serotonergic system presents a challenge for developing the drugs targeting its components: in addition to desirable effects various side effects associated with the same drug are usually observed.