Know Anything About Stress Responses?

[corvus]

Does anyone know much about HPA-axis reactivity and sympathetic vs parasympathetic activation? Well, I know that activation of the sympathetic system is fight or flight stuff and parasympathetic is rest and digest stuff, but I'm wondering what that translates to if during a stressful situation an animal has greater parasympathetic activation than sympathetic? I have a very simplistic understanding of this stuff. I know that no two stress responses are the same, but I struggle with the idea that a stress response could be more parasympathetic than sympathetic. Maybe I'm interpreting this wrong. Maybe it's just more parasympathetic than the alternative coping style, that involves a large sympathetic activation? I don't know what this means! In terms of behaviour.

Sapolsky, why doesn't your zebra book answer this question??

I'm having my own little stress response about this.

[poodlefan]

I know that activation of the sympathetic system is fight or flight stuff and parasympathetic is rest and digest stuff, but I'm wondering what that translates to if during a stressful situation an animal has greater parasympathetic activation than sympathetic?

If I've interpreted that correctly , I think a parasympathetic response to stress would be a shut down - animal freezes and becomes unresponsive. "playing dead" would be the classic example. I have a dog that does this.

A parasympathetic stress response in a zebra would mean a dead zebra in most cases - natural selection wouldn't allow it to proliferate in a herd living prey species as large as a zebra. What snakes and smaller prey animals might get away with wouldn't work for an animal targetted by ambush predators working in teams. It would make you the first animal they reached.

I know some prey species will freeze before chosing flight - but they don't tend to be open plains dwellers.

I'd have throught animals with defensive shells or spines would give parasympathetic responses to stress - they pull up the drawbridge and wait it out.

Edited December 10, 2010 by poodlefan

[raz]

Well, I know that activation of the sympathetic system is fight or flight stuff and parasympathetic is rest and digest stuff,

I thought everyone knew that pretty basic stuff.

[Erny]

I thought that sympathetic over-rode parasympathetic.

[corvus]

If I've interpreted that correctly , I think a parasympathetic response to stress would be a shut down - animal freezes and becomes unresponsive. "

That's how I interpret it, and that's what happens as far as I know. Say you have a dog that freezes with a parasympathetic spike and a dog that flees with a sympathetic spike. If you repeatedly stressed both dogs in the same way, is one going to be better off than the other? If you just did it once, is one going to recover more quickly than the other?

Various studies emphasize the differences between the two coping styles in autonomic balance. Because of the role of the two branches of the autonomic nervous system in cardiovascular control, one may expect in conditions of over-activation of these systems, a differential vulnerability for various types of cardiovascular pathology as well. Indeed, a number of experiments found evidence that the proactive coping animal is more vulnerable to develop hypertension, atherosclerosis and tachyarhythmia due to the high sympathetic reactivity [32,37,47–49]. However, hypertension has never been observed after conditions of uncontrollable stress. In social groups, hypertension generally develops in dominant or subdominant males that have difficulties to maintain their social position. Therefore, it seems that these types of cardiovascular pathology only develop under conditions of threat to control rather than loss of control [15]. The reactive coping style seems to be characterized by a shift in the autonomic balance towards a higher parasympathetic tone and reactivity as can be observed by a strong bradycardia response in reaction to a sudden unpredicted stressor. Although there have been no systematic studies of the cardiovascular consequences of this characteristic, one may suggest that these types of animals are more vulnerable to sudden cardiac death due to bradyarhythmia.

If it's a big, sudden problem, a proactive animal copes better, but if it's a sustained problem, a reactive animal does better? If it's a problem that can be solved a proactive animal is less stressed by it, but if it's a problem that can't be solved a reactive animal is less stressed by it?

[corvus]

A momentary freeze happens all the time in prey animals as they assess what to do next. Usually when they first become aware of a predator they freeze. The sympathetic side kicks in when and if necessary. A lion that's been spotted usually walks away. Best for the zebra not to waste all that energy bolting.

[poodlefan]

Wikipedia says playing dead or freezing is "fleeing in place". So that would still be a sympathetic response. Deep.

A typical example of the stress response is a grazing zebra, calmly maintaining homeostasis. If the zebra sees a lion closing in for the kill, the stress response is activated. The escape requires intense muscular effort, supported by all of the body’s systems. The sympathetic nervous system’s activation provides for these needs. A similar example involving fight is of a cat about to be attacked by a dog. The cat shows accelerated heartbeat, piloerection (hair standing on end, normally for conservation of heat), and pupil dilation, all signs of sympathetic arousal.[6]

Though Cannon, who first proposed the idea of fight-or-flight, provided considerable evidence of these responses in various animals, it subsequently became apparent that his theory of response was too simplistic. Animals respond to threats in many complex ways. Rats, for instance, try to escape when threatened, but will fight when cornered. Some animals stand perfectly still so that predators will not see them. Many animals freeze or play dead when touched in the hope that the predator will lose interest.

Others have more exotic self-protection methods. Some species of fish change color swiftly, to camouflage themselves. These responses are triggered by the sympathetic nervous system, but in order to fit the model of fight or flight, the idea of flight must be broadened to include escaping capture in either a physical way or in a sensory way. Thus, flight can be disappearing to another location or just disappearing in place. And often both fight and flight are combined in a given situation.

The fight or flight actions also have polarity - the individual can fight or flee against or away from something that is threatening, such as a hungry lion, or fight or fly for or towards something that is needed, such as the safety of the shore of a raging river.

A threat from another animal does not always result in immediate fight or flight. There may be a period of heightened awareness, during which each animal interprets behavioral signals from the other. Signs such as paling, piloerection, immobility, sounds, and body language communicate the status and intentions of each animal. There may be a sort of negotiation, after which fight or flight may ensue, but which might also result in playing, mating, or nothing at all. An example of this is kittens playing: each kitten shows the signs of sympathetic arousal, but they never inflict real damage.

[The Spotted Devil]

PF is correct.

corvus, are you talking about perhaps the threshold required to activate the HPA axis??? That, to me, would indicate different coping styles and you certainly see it across a population. Which is why it can be difficult to get a physiological response to stress that is statistically different between treatments.

[Aidan]

The body will always try to achieve homeostasis, as I understand it. So if you have a big fright, your parasympathetic nervous system will need a bigger response when the threat has passed.

[corvus]

corvus, are you talking about perhaps the threshold required to activate the HPA axis???

I think so! I was hoping someone would tell me.

I wasn't sure if HPA-axis reactivity meant bigger responses than normal or a lower threshold than normal. As if normal exists. I would love it if anyone felt like telling me interesting stuff they know about the HPA-axis.

So, if an animal is described as having a high parasympathetic reactivity, what does that mean? Does that mean that animal tends to react to startling or aversive stimuli by freezing? If it has high HPA-axis reactivity and high parasympathetic reactivity, does that mean it tends to freeze at the slightest provocation?

[Jigsaw]

Would it not also depend on the type of stress and innate and learned responses to stress of the individual?

Like if you're out walking in the bush and seeing a snake like object you have that momentary freeze while your brain processes what it is. If you are interested in snakes you may pursue it to learn what type of snake it is and only be mildly aroused with no obvious physical stress. If you're phobic of snakes you may run before your brain even acknowledges whether it is or not a snake and stay alert and "stressed" for some time or even days. If your brain has processed that it is no threat ie just a stick you may walk on but with an elevated heartbeat and hypervigilant senses for a short while until you achieve homeostasis.

And then there's this study if that is any help. Oxytocin can also induce bradycardia. But I'm not a scientist so I might be on the wrong track!

ETA: change produce to induce

Edited December 10, 2010 by Jigsaw

[Nekhbet]

remember this diagram - it will start to help you understand

OK I'm really tired so make me a list of Q's about it because this can be as simple or as complicated as you like. If you know nothing about biochemistry or physiology you're going to have a hard time wrapping your brain around the whole thing.

You have to understand sympathetic and parasympathetic responses are part of the autonomic nervous system - we dont have a say in what happens the body decides for us. Now, do you know anything about negative and positive feedback systems (or the general concept of them anyway) in the way that certain hormones etc feed back to a producing or non producing gland or organ and affect it to either start/stop production?

now a bigger thing, forget the 'fight or flight' BS it just gets in the way.

Edited December 10, 2010 by Nekhbet

[corvus]

OK I'm really tired so make me a list of Q's about it because this can be as simple or as complicated as you like. If you know nothing about biochemistry or physiology you're going to have a hard time wrapping your brain around the whole thing.

I did physiology in undergrad, but wasn't very good at it. I know about feedback systems, though. More recently I read Sapolsky's book on stress, which gives a nice background on glucocorticoids and what happens to the body during chronic stress.

now a bigger thing, forget the 'fight or flight' BS it just gets in the way.

Well, I don't think I should in this case, because I think it's important. I'm looking at the difference between proactive coping styles and reactive coping styles. Proactive animals are the ones that actually seem to do fight or flight sometimes. Their behaviour is characterised by aggression, low attack latencies, and inflexibility. They form routines and then largely ignore environmental stimuli. They explore new areas quickly, but superficially. Reactive animals tend to have low aggression, high attack latencies and behavioural flexibility. When they have a problem, they could try a number of solutions first as opposed to the proactive animals that tend to try aggression first. Reactive animals usually freeze when frightened. They explore new areas slowly, but thoroughly, and tend to not act until changes in the environment make it necessary to act.

I'm trying to tie this in with what is known about their neuroendocrine systems. Proactive animals have low HPA-axis (HPA stands for hypothalamic-pituitary-adrenal for those that were wondering) reactivity and high sympathetic reactivity during a stress response. Reactive animals have high HPA-axis reactivity and high parasympathetic reactivity during a stress response. What does it mean to have high or low HPA-axis reactivity? How do the behaviour and the neuroendocrine system relate to each other?

[JulesP]

Sometimes the freeze happens when flight or fight aren't possible.

[Nekhbet]

I meant fight or flight concept will give you a preconception towards the whole picture hence toss it not that it's useless.

How do the behaviour and the neuroendocrine system relate to each other?

go back and pick up your physiology textbook first and have a good read about sympathetic and parasympathetic. Actually have a quick read of this http://www.medicinenet.com/stress/page5.htm some more on the next pages about the affect of hormones and HPA axis on emotion and behaviour, not complete but it gives you a start.

[corvus]

I meant fight or flight concept will give you a preconception towards the whole picture hence toss it not that it's useless.

I'm not sure if I've already tossed it by your definition or not! I get that every stressor has a different stress response and that fight and flight often aren't involved. But in this particular case that I'm interested in these proactive animals are jumping in to fight when they don't really need to and other animals are not doing either and coping with the same stressor in a perfectly satisfactory manner. I'm not talking about fight and flight in the traditional binomial kind of sense. I'm talking about it in the sense that some individuals do it more than others even when they don't need to.

How do the behaviour and the neuroendocrine system relate to each other?

go back and pick up your physiology textbook first and have a good read about sympathetic and parasympathetic. Actually have a quick read of this http://www.medicinenet.com/stress/page5.htm some more on the next pages about the affect of hormones and HPA axis on emotion and behaviour, not complete but it gives you a start.

I never bought the textbook, which is possibly why I wasn't very good at it.

Thanks for the link. I read through it, but didn't find it answered any of my questions. I know what they all DO and the basics of how they do it and the anatomy involved, but what does it mean in relation to having two animals, one stressor, and two wildly different stress responses - one characterised by sympathetic reactivity and low HPA-axis reactivity and the other by parasympathetic reactivity and high HPA-axis reactivity. I feel like I'm not making a lot of sense, but don't know how to phrase what I want to know so that it makes more sense. What does high reactivity or low reactivity mean in this context? Does it mean the system is more sensitive? Does it mean the stress response is stronger or more prolonged?

I've got the behavioural facts I know in one part of my mind, and the related neuroendocrine facts in another part of my mind, but I can't quite marry them so I understand what the full picture is and why these things are apparently linked.

[The Spotted Devil]

Hey corvus.....does this help? From a chapter in 'The Inevitable Bond' but not the primary reference...

Dominant wolf cubs have higher baseline heart rates than submissive cubs

Dominant animals display primarily adrenomedullary and catecholamine arousal, animals that are less dominant but still aggressive experience both and submissive animals respond with the adrenocorticol system only. Thus they use a coordinated series of responses (behavioural, cardiovascular and endocrine) as the means to a common homeostatic end.