According to P. Whybroy (1985), depression can be defined as the feedback of three sets of variables at the level of biochemistry, life experience and behavior, and the anatomical substrate or field of interaction of these components is the midbrain.
Neurobiological processes occurring in the nervous system affect the behavior of a patient with depression, and, on the contrary, human behavior affects the state of neurobiological processes.
It is believed that the onset of depression coincides with the onset of the destructive pathological process in the region of the intermediate section of the brain stem. The region of the midbrain becomes the sphere of intersection of psychological and biological processes that constantly accompany depression (Akiskal H., McKinney W., 1975).
This assumption is indirectly supported by the results of neurophysiological, pharmacological and endocrinological studies: the weakening effect of alpha-2 agonist clonidine in response to the growth hormone secretion, a decrease in the duration of the latent period of sleep with rapid eye movement, disruption of circadian rhythm of sleep, increased melatonin suppression during phototherapy, depression ACTH reaction in response to the action of corticoliberin, an increase in blood cortisol with a violation of the daily rhythm of this hormone (resistance to dexamethasone), reduction of the stimulating effect of synthetic thyroliberin in response to the secretion of thyroid-stimulating hormone (TSH).
Of particular interest are disorders arising during the period of depression in the limbic system of the brain, which is responsible for the regulation of emotions and other physiological changes. The limbic region consists of several structures and includes the hypothalamus – the center responsible for eating behavior, sleep, human sexual activity, stress response, etc. The hypothalamus controls the pituitary gland – a kind of “conductor” of the endocrine system that regulates the production of various hormones in other endocrine glands. In addition to the hypothalamus, the hippocampus and the amygdala are complex bodies of the brain that regulate human motivational activity associated with his drive and memory
During prolonged depression, an extension of its lateral ventricles was discovered with the help of modern methods of brain research – neuromorphology and neuroimaging, probably indicating destruction and atrophy of nerve cells of brain structures such as the hippocampus (Stoll A. et al., 2000).
Each brain nerve cell, or neuron, consists of a body, from which the long process, the axon, departs, and a whole series of shorter processes, the dendrites, which receive the nerve impulses. They accumulate in the body of the nerve cell, later accumulating in the axon, transfer to many of its branches, and are transmitted again to the dendrites of another neuron.
It was found that in the situation of chronic stress, atrophy of the processes of pyramidal cells occurs – dendrites of neurons of those brain structures (the SAZ field of the hippocampus), which are close to its stem sections. The introduction of certain antidepressants (for example, tianeptine) before the onset of stress prevented the destruction of the nerve cell (Watanabe Y. et al., 1992).
It is known that neurons are grouped in the nerve centers of the brain that specialize in certain types of functional activity.
Depression researchers have found an increase in the number of nerve cells in the nuclei of the hypothalamus. As noted above, the latter is a region of the brain in which the functions of the nervous and endocrine systems of the body are integrated. This is where the main inclinations of a person are formed, the rhythm of sleep-wakefulness, and it is here that mediators that according to modern views are related to depression play an important role. We are talking about norepinephrine, dopamine and serotonin.
The significance of the biological factor in the origin of depression is confirmed by changes in hormones that are found in this state — chemically active substances that are produced in the body by the endocrine glands. As you know, hormones control the physiological functions of the body and, in particular, its response to stress. However, it remains unclear the answer to the question: what is the primary element of the pathogenesis of depression – changes in the endocrine glands, general hormonal levels, or the actual mood swings.
In the period of depression, violations are detected in at least two endocrine axes or systems: the hypothalamus — hypophysis — adrenal glands, and the hypothalamus — hypophysis, the thyroid gland. It is assumed that during the depression the endocrine system feedback mechanism is disturbed, which ensures the processes of independent regulation of the hormone content by the body. In patients with severe depression, the hypothalamus constantly stimulates the pituitary gland, regardless of the content of hormones in the blood.
Probably, endocrine disorders can be attributed to trophic disorders of the nutrition of tissues during depression: hair loss, increased fragility of the nails, weakening of the skin elasticity, the rapid appearance of gray hair. Rather typical for depression and hyperglycemia – high blood sugar levels of the patient.
During the depression period, a violation of the two main functions of the hypothalamus was noted. On the one hand, the nerve cells of this area of the brain begin to actively release substances that stimulate the secretion of hormones of the adrenal cortex, on the other, the sensitivity of the latter to the adrenocorticotropic hormone of the pituitary, which increases the activity of the adrenal glands, increases.