Neurostransmitters and Depression
Some observations have suggested that certain changes in the body may lead to a depressive disorder. For example, the association of a number of physical illnesses and depression, or relationship of the effect of antidepressant drugs with changes in brain neurotransmitters, the existence of other drugs that can cause depression, the depression induced by drug use, and genetic transmission mechanisms which favor the occurrence of depression in several generations of one family.
In terms of genetic origin. We have seen that major affective disorders (those mood disorders with greater intensity and duration) occur more frequently in relatives of diseased subjects. It is accepted that heredity plays a role in the genesis of depression. However, the fact that there are different types of depression with age at presentation, response to treatment, course, difficult to study the type and mechanism of transmission of each one of them.
Studies of family history of depressive disorders reveal an increased rate of affective disorders in relatives of healthy subjects. When studying patients with adopted mood disorder is found that the frequency of mood disorders is higher in non-biological parents in their adoptive parents. Also investigated whether in identical twins (called monozygotic) the agreement for the two presented a depression is higher than the fraternal twins (their genetic material is not so similar), and has been seen that the concordance rate for affective disorder is higher in the former. Few studies of twins raised apart also confirms genetic inheritance. Genetic studies are in populations with major depressive disorders.
Biochemical hypothesis (neurotransmitters). The biochemical hypothesis evolved from clinical observations that linked the administration of a drug, reserpine, with the emergence of depressive symptoms. Reserpine produced depletion (decrease) in brain neurotransmitter substances such as noradrenaline. The role of neurotransmitters is to establish a code of electrical and biochemical signals to be secreted by a neuron and interact with adjacent neurons, whose membrane there are receptors for these neurotransmitters.
This code is determined genetically but can vary depending on external variables .. In man, described several diseases that result from an alteration in the code, known as neurotransmission. Schizophrenia and depression are now considered diseases of neurotransmission days. There are studies investigating the genetics of depressive disorders and investigate variants of genes coding for these neurotransmitters. The exact role of neurotransmitters is subject to constant debate.
Researchers and doctors initially focused on the hypothesis that low levels of neurotransmitters and, therefore, a deficit in neurotransmission produces depression. The most studied neurotransmitters are norepinephrine, serotonin and dopamine, on the grounds that the effect of many antidepressant drugs go through a change in these neurotransmitters or their receptors. Efforts to identify consistent biochemical abnormalities in patients with mood disorders have been only partially successful. These efforts include the determination in different body fluids (blood, urine, cerebrospinal fluid) of these neurotransmitters and their metabolites (compounds produced in the wake of these substances by points of the body-the liver, where they are transformed).
Found arguments that incomplete theory to explain depressive disorders, as we have said that there is no single explanation for all depressions. Some research has been very focused later in the study of the functioning of receptors and their subtypes, detecting variations in performance, such as the increase in density in the membrane of the neuron or are more or less sensitive the effect of neurotransmitters. Recipients are also responsible for the transmission of electrical signal.
It has also been observed that several types of antidepressants and electroconvulsive therapy (ECT) produces the effect of decreasing the density of receptors on the membrane. Same as the above theory is not worth to explain all cases. It suggests, in general, the effect of antidepressants would pass through the stimulation of serotonin neurotransmission, rather than adrenaline. To all this must be said that neurotransmitter systems in the brain does not function independently of each other and this adds much complexity to the investigation of biochemical alterations in the depressions.
Finally, serotonin and noradrenaline are just two of many neurotransmitters and neuromodulators that exist in the brain
Neuroendocrine system. The hormonal secretion system of the body works in interaction with the nervous system and is also influenced by external agents.
In depression are changes in the functioning of so-called hypothalamic-pituitary-suprarrenal.Estas three glands (the hypothalamus and the pituitary gland in the brain and adrenal glands above the kidneys) operate synchronized to each other, so that the hormone secreted by the hypothalamus stimulates the pituitary to produce another hormone, which in turn stimulates the adrenal glands to produce cortisol.
In turn, the amount of hormone secreted brake serves stimulating the gland, called a feedback mechanism. It seems that in depression this feedback response does not function normally and in disorders such as major depression have elevated levels of cortisol (produced by the adrenal glands).
We also observed high levels of hormones produced by the hypothalamus and pituitary, which are corticotropin-releasing factor and corticotropin, therefore, in certain types of depression are not the self-regulatory function of the hypothalamic-pituitary-adrenal and hormones produce above normal levels. Neurotransmitters such as serotonin or norepinephrine secretion partly regulate the hypothalamus.
For many years, abnormalities of the thyroid gland function have also been associated with mood disorders, hypothyroidism and sometimes gives the face a depressive syndrome. As in the previous case exist in certain cases of depression, poor regulation of hormone secretion from these glands.
Organic depression. There depressive appearing in the context of medical illness and we provide evidence of the influence of biological factors. Among the diseases of the central nervous system (CNS) has been observed that 25-40% of patients with certain diseases present a major depressive disorder at some time during the course of the disease. These include disorders such as Parkinson’s disease, Huntington’s Korea, cerebrovascular disease (strokes, heart attacks, bleeding), dementia, multiple sclerosis, epilepsy, head trauma, CNS tumors, Wilson’s disease.
In the medical conditions that do not involve the CNS directly the rates are much more variable and range from more than 60% in Cushing’s syndrome to less than 8% in end-stage renal failure. The tables associated with endocrine diseases are most associated with neuropsychiatric disorders (hyperthyroidism, hypothyroidism, Cushing disease, Addison’s disease). Other diseases associated with depression are sometimes rheumatic diseases (systemic lupus), neoplasms (cancer of the head of the pancreas), infections (virus).