Introduction
This page is the third part of a study of articles.
An overview on stress neurobiology: Fundamental concepts and its consequences by Rumi Iqbal Doewes, Lekshmi Gangadhar and Saranyadevi Subburaj
The hippocampus
The hippocampus receives input from many regions including the dentate gyrus and the entorhinal cortex.
It also sends both excitatory and inhibitory messages to various regions. These outputs result in indirect inhibition of impulses to the PFC.
The hippocampus also sends to the PFC and the BLA. These connections are important in memory and the management of reactions to psychological stress.
The relation of the hippocampus and the BLA goes both ways, meaning they both send to and receive from each other.
During moments of strong emotions, these links are activated while the PFC, that would suppress the amygdala, is inhibited. This enables the creation of long term flashbulb memories.
Flashbulb memories
Memories of the circumstances of when a very surprising event happened.
Stress and genetics
There are many ways that stress has an impact on the genes.
An example is glucocorticoids. These hormones, released in response to stress, have an impact on the activation of transcription and the stimulation of epigenetics.
Lab experiments have found that stress, in all forms, blocks certain genes in the hippocampus although these changes were different for each situation.
In addition, corticosterone alone wasn’t able to produce the same changes meaning it isn’t the only factor.
These changes may have long term effects as rats expressed to extreme stress for 3 weeks did not return to completely the same state. Stress reactions were also found to be different.
The molecules in stress
Several molecules are releases during stress.
Glucocorticoids are of course one. Another is the corticotrophin releasing factor(CRF).
This is involved in the HPA axis but also in the stress induced remodelling of the dendrites in a region of the hippocampus.
Corticotrophin release factor
CRF or corticotrophin releasing hormone (CRH)
A hormone secreted by the hypothalamus and the regulator of the HPA axis.
When released, it causes acethylcholin and glucocorticoid to be released.
The acethylcholin will then bind to the adrenal cortex, releasing cortisol in humans or corticosterones in other mammals.
The Tissue plasminogen activators, whose release is stimulated by the CRF, is also involved in the remodelling of dendrites by stress but also in the loss of spines in the same region and the MeA.
Lipocalin-2 is another molecule released during stress as well as Endocannbinoids and BDNF.
Endocanabinoid
Regulate the structural changes in the brain that end the short term response to stress and familiarize to repeating stressors.
BDNF
Brain derived neurotropic factor
A protein released from the hypothalamus, involved in plasticity an transmission.
In stress, it is involved in the remodelling of dendrites.
Part 1 : The amygdalas reaction to two different stressors
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