Before we discuss the difference between an agonist and an antagonist, I have a story to relate to our topic.
In our childhood, we used to play video games on an Arcade Machine. Computers were not a household item back then, and those bulky Arcade machines were to be found inside a video game shop. Before starting a new game, one would have to insert a coin. The coins cost more than the lowest currency coins available at that time. Some of us would use these coins to mimic the behavior of a normal game coin. However, there was a problem. Sometimes, these coins get stuck in the game and block space for new coins.
Now think of a normal game coin as a ligand. A ligand is a natural substance that binds to a specific receptor protein in a cell. Upon binding a ligand, receptor proteins can alter their shape or behavior, resulting in a specific response.
In our example, the currency coin acts as an agonist because it mimics the action of the ligand. If a natural ligand is absent or not present in sufficient amounts, we can use an agonist in its place to obtain the desired effect. If a currency coin gets stuck in the arcade machine, it is similar to what an antagonist does. An antagonist attaches to the receptor protein and blocks the agonist’s access to it, preventing it from binding to the receptor protein.
Agonists vs Antagonists in Pharmacodynamics
Pharmacodynamics refers to the effects and the mode of action of drugs within the body.
To produce a response within the body, drug molecules have to travel down to their specific receptors.
Receptors are specialized proteins that are present either within a cell or on its membrane. Normally, these receptor sites have natural ligands that bind to and produce certain changes in them, either chemical or physical. Ultimately, this affects the cell’s structure and behavior.
Think of an agonist as an alternate key for the same lock, which is the receptor. While the ligand is the original key, the antagonist represents an incorrect, rather a faulty key that prevents the correct keys from opening the lock. Sometimes, it can damage the lock, rendering it unable to open even with the original key.
Now it is time to redefine ligands, agonists, and antagonists.
A ligand is a natural substance that binds to a specific receptor.
An agonist is a medication that mimics a ligand’s behavior. It binds to and activates the receptor exactly the way an agonist does.
On the other hand, an antagonist is a medication that binds to a receptor but doesn’t activate it. By doing so, it renders a receptor unable to be activated by a ligand or an agonist.
Agonists vs Antagonists in Psychology
Neurotransmitters are the natural ligands in a neuron. These chemical messengers are fired from a neuron across the synapse, a small gap between a neuron and a target cell. Neurotransmitters bind to and activate the target cell. The target cell can be another neuron, muscle cell, or gland cell.
Neurons in most brain areas are specific to the neurotransmitters they release and receive. What it means is that we can supply agonists and antagonists for these neurotransmitters for medical and recreational purposes. Neurotransmitters have specific roles, and we can use different agonists and antagonists to produce desired responses.
Agonists are drug molecules that bind to synaptic receptors and enhance the effect of a neurotransmitter.
Antagonists are drug molecules that also bind to the same synaptic receptors, but they decrease the effect of a neurotransmitter by blocking its way to the receptor site.
If, for example, a neurotransmitter is excitatory, an agonist will increase its effect while an antagonist will decrease it.
On the other hand, if a neurotransmitter has an inhibitory role, an agonist will increase its inhibitory effect, and an antagonist will decrease it.
Endorphins like opium, codeine, and morphine are agonists to dopamine as they complement its effect for causing pleasure or reducing pain.
Chlorpromazine and haloperidol are the antagonists for dopamine as they block its receptors, rendering it unable to bind to them, minifying the role of dopamine to heighten pleasure.
I hope you’ve got a decent understanding of what agonists and antagonists are. If you want to know more about the difference between an agonist and an antagonist, let me know in the comments.