An individual exposed to stress can usually rapidly adapt the own behavior to the specific situation. Biochemical messenger substances in the brain play a central role in this rapid transformation process. We know that hormones additionally have a stress regulating function, but that their effects are more slowly apparent. Using a combination of optical and genetic techniques, the research team has had the capacity to show that corticotrophs, the cell populations that prompts the adrenal cortex and produce the stress hormones of the hypothalamic-pituitary-adrenal axis, will quickly impact avoidance behavior immediately after the onset of a stress situation. This insight could add to the development of effective treatments which will facilitate the management of acute stress induced reactions or may even have the capacity to mitigate acute stress associated conditions.
The human body is controlled by the hormonal system and the nervous system. The hypothalamus situated in the middle of the basis of the brain has a key role here providing the link between the body and the different regions of the brain similarly as directly and indirectly controlling a progression of essential physiological vegetative functions. In addition, it is the most important control organ of the human endocrine system, because it regulates when and how much of a hormone is produced. Both the hypothalamus and its production of hormone are also subject to the impacts of emotional stress. The pituitary gland is connected to the hypothalamus and together they form a single functional unit called the hypothalamic-pituitary-adrenal axis.
Hormones secreted by the hypothalamus incorporate the supposed releasing hormones, such as the corticotropin-releasing hormone. This stimulates the production of the adrenocorticotropic hormone in the pituitary gland. The adrenocorticotropic hormone is a hormone secreted by the anterior lobe of the pituitary and it regulates the production of other hormones, such as the stress hormone cortisol.
It can be basically assumed that the neurotransmitters of the CNS quickly determine whether fight or flight behavior is to develop in a given situation. To date, medical science has conjectured that the stress-regulating effects of the hormones of the HPA axis come into play far more slowly. Stress researchers found it very problematic to establish the concrete role of the hypothalamic-pituitary-adrenal axis in the rapid adaptation of behavior in a stress situation in more detail in standard animal models. This is because the location of the pituitary gland and hypothalamus in mammals makes them difficult to access. To overcome these obstacles, the researcher decided to create an innovative optogenetic research technique. They managed to develop a hereditarily modified zebrafish larva in which they had the capacity to manipulate the activity of the HPA axis using light and subsequently observe the resultant changes to the responses of the altered cells.
The researchers introduced a synthetic enzyme into their animal model that elevates the levels of the intracellular messenger substance cyclic adenosine monophosphate (cAMP) only in the corticotropic cells of the hypothalamic-pituitary-adrenal axis. Their rise is important for the release of hormones in the corticotropic cells of the anterior pituitary. The levels of the resulting so-called transgenetic animal stress hormones can be increased by means of exposure to light. This means the researchers can thus observe the accompanying changes to behavior.
The recently published research results that the corticotropic cells in the pituitary become directly active on the beginning of a stress situation that is seen as distressing. These then influence locomotion and avoidance behavior as well as the sensitivity to the stimulus. The specialists translate this as proof that the corticotropic cells in the pituitary play a significant role in the rapid adaptation of behavior to local environments identified as antagonistic.