Gunnar – brain and stress

The brain is one of the major target organs, as we talk about it, for the stress hormone that I study: cortisol. There are many receptors for cortisol in the brain in very different regions. Whether or not you want to talk about it as a problem for the brain or what the brain is supposed to be doing, you see effects of this hormone on the brain. To understand these effects, you need to know that there are two different kinds of receptors for this hormone. One kind is called the MR receptors and these are typically occupied, that is, the hormone is hooked to the receptor causing the receptor to make the cell do what it’s supposed to do. These are typically occupied when cortisol is in its base or typical non-stressed range. Those effects tend to be what we call promotive. They’re healthy for the brain. They help support the brain doing sort of healthy, growth-promoting things. As the hormone rises into the stress ranges the other receptor, called a GR receptor, begins to be occupied. The GR receptor tends to do and trigger those events that are energy demanding of the cell. And many of the effects we talk about as being challenges or threats to the brain are due to the fact that you get the cell operating in a very energy demanding mode.  

But it reduces the ability of the cell to take up glucose which feeds the energy processes. So what you get are cells that are threatened because they’re working very hard and they aren’t able to pick up the energy that’s necessary to return them to a quiescent state. So you do actually see changes in dendrites, the connections between brain cells, in high energy use areas like the hippocampus which is an area that’s involved in memory and the dendrites begin to be sort of curled back and not as able to talk to one another. Or you actually see death of cells in these high energy use areas like the hippocampus. So one!  implication of this is with very high levels of this hormone over long periods of time, which the body doesn’t like you to do, it tries to fight against that, you do see reductions in memory abilities, specifically what we call episodic memories. Memory for explicit events like where you parked your car this morning. And so you see those things. 

In another area of the brain the amygdala, which is very involved in emotion processing, cortisol actually seems to up regulate or increase the activity there. So that with chronic stress exposure you get an area of the brain being on sort of a hair trigger for receiving and responding to threat and a memory capacity that’s reduced. Those are two of the kinds of effects that people have looked at the most because we can model them in animals. Cortisol also has lots of receptors in the frontal regions of the brain which are involved in what we call higher order thinking: working memory, ability to plan, ability to inhibit behaviors, and so on. 

Here we don’t really know as much about what cortisol is doing. And probably the other thing for your students to realize is this system tends to operate in an inverted u-shaped pattern. Too little isn’t good, too much isn’t good, it’s like Goldilocks and the Three Bears. There’s a range of this hormone that’s promotive of healthy adaptation. So it’s not like we want to say “Let’s get rid of this hormone from the body.” “Let’s never react to stress.” Not true. What you’re looking for, with healthy adaptation is a moderate stress response but it can be turned off and you get the benefits and you avoid many of the costs of stress.