What causes dialation/constriction?

[wastedwalrus]

Technically speaking, why do so many drugs affect the eyes? Constriction, dialation, red-eye..... what aspects of drugs cause these effects? I know what drugs do these things but I want to understand it more. Thanks.


Also, if you don't mind, a quick question.... Do most people experience pupil dialation from cocaine?

 

[Enlitx]

As to the second part of your question, cocaine is a powerful stimulant, and when the sympathetic nervous system is activated the pupils tend to dilate.

 

[fishman]

Doesn't it all just have to do with acetylcholine and norepinephrine? The more acetylcholine released, the more pupil contraction. The more norepinephrine released, the more pupil dilation. NOW, what initiates the chain of signalling events that leads to such releases is the real question, right?

Check out this quick synopsis:

http://www.elmhurst.edu/~chm/vchembook/661nervoussys.html

 

[BilZ0r]

Pupil dilation from cocaine and from any other stimulant is easy. They release noradrenaline. Noradrenaline causes the pupils to dialate through alpha1 receptors (think about if you were an animal, in the jungle, and you got a fright i.e. a predator, you would need your pupils as wide as possible to see it... frights release noradrenaline). MDMA, meth, cocaine fit into that catagory.

Why pure hallucinogens cause this effect, I'm still unsure.

 

[Vaya]

What about opiates, BilZOr? What is the mechanism of action by which the ingestion of an opiate/semi-synthetic opioid/fully synthetic opioid causes constriction of the pupils?

Are there any other recreational substances out there that you (or anyone) knows of which also cause pupil constriction?

 

[BilZ0r]

It's because of Mu and kappa receptors, I believe this is because they simpley inhibit noradrenergic input, I'm not 100% sure though.