Catecholamines (part III)
Epinephrine (Adrenaline):
Where:
- Synthesized in adrenal glands
- Synthesized in much smaller amounts by certain neurons located within the medulla oblongata
- increased blood flow to muscles
- increased cardiac output
- increased blood sugar level
- increased heart rate
- pupil dilation
- vasodilation
- bronchodilation
- Brain norepinephrine primarily synthesized in nuclei such as locus coeruleus (LC)
- Small quantities secreted directly in to the bloodstream by adrenal glands
- Used as a neurotransmitter by sympathetic ganglia located near the spinal cord and in the abdomen
- increases mobility
- increases feelings of arousal, stress, alertness
- promotes vigilance.
- enhances abilities related to memory recollection and formation.
- Improves focus and attention
- Also increases restlessness, anxiety, heart rate, and blood pressure
- Increases blood flow to skeletal muscles while reducing blood flow to the gastrointestinal system
- makes it harder for you to shit yourself
- Triggers release of glucose from energy stores
- Synthesized in the brain and kidneys
- Also synthesized in plants and most animals
- increases mobility
- increases feelings of arousal, stress, alertness
- promotes vigilance.
- enhances abilities related to memory recollection and formation.
- Improves focus and attention
- Also increases restlessness, anxiety, heart rate, and blood pressure
- Increases blood flow to skeletal muscles while reducing blood flow to the gastrointestinal system
- makes it harder for you to shit yourself
- Triggers release of glucose from energy stores
Effects:
Epinephrine or more commonly known as adrenaline was first isolated in 1895 by Polish physiologist Napoleon Cybulski.
One of the primary functions of epinephrine is to prepare our bodies for physical duress, most notably where it plays a vital role in the fight or flight response. The increased cardiac output induced by epinephrine allows oxygen rich blood to reach your muscles faster which allows them to work harder. Additionally epinephrine raises our bodies blood glucose levels to allow your cells to take in more glucose to use for energy. Studies have also shown that epinephrine secretion can also be physiologically stimulated via exercise.
More recent studies have also investigated the relationship between epinephrine and certain emotions, the most focused of which has been fear. One experiment had subjects watch fear films, one group was injected with epinephrine prior to watching the film while another control group wasn't injected with anything. The subjects that were injected with epinephrine reported a more intense fear from the films and greater mean intensity of negative memories than control subjects. Additionally subjects injected with epinephrine expressed more negative and fewer positive facial expressions to fear compared to a control group. The main takeaway from this study is that there is a clear correlation between epinephrine concentrations and negative emotions such as fear. Other studies have attempted to also find links between epinephrine levels and other emotions such as anger and amusement, however no evident correlation has been identified.
In medicine one of the most common uses of epinephrine is as a physiological antagonist to histamine during anaphylaxis. Epipens which are prescribed to individuals who are at risk of severe allergic reactions are just epinephrine injections. I don't want to dive too deep on this topic though as I cover it more thoroughly in the prior article on Imidazoleamines.
Fight or Flight:
The fight or flight response is a physiological response to something an organism would perceive as threatening. For example if you encountered a hungry lion chances are you'd perceive it as being quite threatening. Blood flow to your muscles would increase as would your cardiac output. Your pupils would dilate allowing more light to enter your eyes. Your body has evolved to recognize threats and automatically prepare itself for physical stress when it needs to most. In the context of our example, your body wants you to either fight the threat or escape it. This is essentially an oversimplification of the fight or flight response.
Norepinephrine (Noradrenaline):
Where:
Effects:
You might notice that norepinephrine and epinephrine have similar names as well as side effects on the human body. This is because both frequently work conjunction with each other and also play vital roles our bodies fight or flight response. Another noteworthy thing about norepinephrine is that it is actually the main neurotransmitter used by the sympathetic nervous system. Unlike many of the monoamines on this list, norepinephrine is much more of generalist and has varying effects on many different organs and cell types. In a very broad sense norepinephrine's primary purpose is to modify the state of an organ so that it becomes more adjusted to active body movement. This usually results in more wear and tear as well as energy being consumed by said organ. Additionally the concentration of norepinephrine within the brain tends to be fairly low while somebody is sleeping, especially during REM sleep and increases steadily as a person wakes up and becomes more active. From there it's concentration tends to baseline throughout the day until certain stimuli temporarily increases the concentration of norepinephrine within the LC. Some of these unpleasant stimuli include pain, difficulty breathing, bladder distension, heat or cold generate larger increases.
Additionally fear and pain have been associated with higher amounts of norepinephrine within the LC. Greater LC activity is often associated with greater vigilance and reaction as the locus coeruleus is one of the main sections of the brain responsible for releasing norepinephrine. Norepinephrine induced stimulation of the locus coeruleus enhances processing of sensory inputs, vigilance/attention, and the formation and retrieval of both long term and working memory. Additionally LC activity stimulated via norepinephrine has also been linked with an enhanced ability for the brain to respond to inputs by changing the activity pattern in the prefrontal cortex and other areas.
Many drugs leverage these mechanisms to produce desired effects, Adderall (amphetamine) increase the concentration of brain norepinephrine to improve vigilance and memory formation and retention. Check out my more detailed post on the mechanisms behind Adderall. On the other hand other drugs designed to suppress LC activity have a very powerful sedating effect.
Dopamine:
Where:
Effects:
Dopamine is the chemical that degenerates blame their addiction on. Just kidding, while dopamine does a play significant role in our bodies motivational components and reward-motivated behavior this is only one of several brain dopamine pathways. Other pathways include playing a role in motor control as well as in controlling the release of certain hormones.
In recent years dopamine has been popularized by the media which has led to a few misconceptions. It is commonly thought that dopamine is the chemical of pleasure which is somewhat deceiving. In reality dopamine plays more of a role in the anticipation of a reward more so than the reward itself. In other words anticipating a reward is what increases brain dopamine levels and is what propels you towards a reward. The reward-motivated behavior pathway of dopamine serves the purpose of motivating an organism towards a desired outcomes. Common activities that lead to dopamine release such as sex, or eating good food serve an evolutionary purpose. In nature humans who ate the best and reproduced the most were the fittest and became far more likely to pass on their genes. However modern times have lead to some of these mechanisms being exploited such as with sugary foods or drugs. Many addictive drugs work by increasing brain dopamine levels by blocking re-uptake of synaptic dopamine or by increasing its release. This often leads to addiction and is generally unfavorable to the organism.
It's also noteworthy to mention that dopamine plays many roles outside the central nervous system. It plays a role in the endocrine system, acts as a vasodilator and inhibits norepinephrine release, it plays a role in insulin secretion within the pancreas, increases sodium excretion and urine output in the kidneys, and much more. In mammalians of dopamine receptors have been identified so far and there are still still many unanswered questions surrounding this chemical.
Anyways even though this was a very broad overview of how monoamines work hopefully I have piqued your interest further into the biology behind these chemicals.
