Ah, the exception to the rule. If you are on this page for the first time, go ahead and scroll down to the earlier posts so you know what the heck I’m talking about. If you get it already, then nevermind! Carry on!
First of all, I want you to dig back in that Rolodex of your mind and think about the nervous system. Remember that the Peripheral Nervous System (PNS) goes out into the body to send efferent signals, and receives afferent signals to bring back to the CNS. Well the PNS is full of alpha-1, beta-1, and beta-2 receptors. Alpha-2 receptors are there too, but their main function is to stop NE release presynaptically. We actually don’t have much therapeutic use for those particular PNS alpha-2 receptors, so generally we ignore them*.
The alpha-2 receptors we need to worry about are the ones in the Central Nervous System (CNS) and they are very important! There are two main functions of these important receptors:
1. Reduce the sympathetic efferent signals from the CNS (so reducing adrenergic response in the PNS)!
2. Reduce the perception of severe pain, especially neuropathic pain.
You may have noticed that these adrenergic receptors do not prepare you to run from tigers like the other ones do. The best way to remember this is that they are located in a different area. They still control sympathetic stimuli, but they do it higher up in the chain. Alpha-2 receptors in the CNS are the Dictators of the adrenergic receptors. “No, alpha-1, you SHALL NOT BE ACTIVATED!”. Or something like that.
*There are many MANY things that need to be learned about all receptors, so it’s handy to just acknowledge that PNS alpha-2’s are there on the synapses, just in case you decide on further research! For the purposes of common drugs, just put those guys on the back burner.