overdose: neurotransmitter


  • A neurotransmitter in the brain and local chemical messenger outside of the brain, dopamine has various different effects in the body
  • Dopamine plays a big role in reward-motivated behavior which is exhibited by an increase in dopamine levels in the brain.
  • Many drugs, such cocaine, amphetamines, and methamphetamine work by amplifying the effects of dopamine, a characteristic that researchers theorize makes them so addicting.
  • Dysfunction of the dopamine system is responsible for many diseases such as Parkinson’s and potentially schizophrenia, ADHD, and restless leg syndrome.
  • In addition to the reward system, dopamine also has important roles in motor control, motivation, arousal, lactation, and sexual gratification.
  • Outside of the brain, dopamine has a repressive effect on tissues of the immune system, specifically lymphocytes. Currently, this is being studied to find the link between the nervous system and immune system and dopamine’s potential role in autoimmune disorders. 
  • Dopamine is an important precursor for the synthesis of two other neurotransmitters; epinephrine and norepinephrine

(Blue is an amine and red are hydroxyls) 

The Mesencephalon is Messy

I swear I did not intend for one of my first posts to be about one of the ‘cephalons. However, it’s a tough one to avoid in neuroanatomy, especially upon the discussion of neurotransmitters!

Yes, this photo is actually from my textbook, because the internet does a mediocre job at sufficiently demonstrating what and where the mesencephalon really is within the brain. (A little note: a study partner and I remembered the structures within the mesencephalon by calling it “messy”. A lot of stuff fits into that little area of our brain, and it is also very colourful!) This is crucial because locations of structures within the brain are significant of what structures they talk to, and sometimes what functions they serve. I’m really only going to talk about a few structures labeled above, but it is a good refresher to see what the mesencephalon is.

Example A: The Mesotelencephalic Dopamine System!

The substantia nigra (which means black substance) secretes dopamine to send to the basal ganglia for motor control. In patients with Parkinson’s Disease, you will see the substantia nigra decrease in its dark pigment due to the death of dopamine-generating cells. However, it is still significantly difficult to tell from an MRI alone if a patient has Parkinson’s.  Diagnosis is also mildly difficult because patients may exhibit a lack in facial movement/expression that can be mistaken for depression, when it is actually due to their inability to move as they would normally. Unfortunately, with the progression of the disease, patients often due become depressed if their quality of life decreases significantly as a result, or simply because dopamine is not being sent to the brain’s reward center anymore, which I’ll discuss later.

Generally, people mistake one of the most common diseases of this structure to be an increase in movement. Parkinson’s Disease is actually a decrease in movement because the substantia nigra is no longer generating the dopamine that communicates with the basal ganglia, which aids in movement. The medicine prescribed for Parkinson’s contains a level of dopamine to “jump” the system and get things moving again, and because the body can’t generate its own dopamine, this intake of causes the patient to have uncontrollable shakes. There is no way to give a patient “just enough” dopamine to get a level of non-shakiness and movement. Since the body is constantly using it to navigate, dopamine must be administered at higher amounts in order to elongate the effectiveness of the medication.  Patients will generally experience a half an hour, if that, of normal movement during a dose of medicine.

MRI comparison between a normal patient and a patient exhibiting Parkinson’s within the substantia nigra.

The substantia nigra also works alongside the ventral tegmental area (a series of cell bodies of many neurons) to communicate to various parts of the brain. One in particular being the nucleus accumbens,which is responsible for your addiction to DRUGS!

… Okay, okay. The nucleus accumbens is also your reward center for many other actions.  So any time you get that A on an exam you totally thought you failed, and you call mom and dad and grandpa and take people on the sidewalk by the shoulders, yelling, “I GOT AN A!” (I mean, who doesn’t do that?) that’s your dopamine, running from your substantia nigra to your nucleus accumbens like, GO GO GO GO GO GO GO! And your brain is able to do this through a series of neurons firing the signal to make more dopamine, and more dopamine, and MORE dopamine.

The Mesotelencephalic Dopamine System is also responsible for communicating with many other parts of the brain which conduct other functions, but these two specific instances provide most of what dopamine has to offer!

Neurotransmitter Definition and Criteria

I realized that in this blog there’s a lot of mention of neurotransmitters, but I had never really posted the definition and the 4 criteria requirements for the classification of a chemical as such. 

In Principles of Neuroscience, Kandel, Schwartz and Jessell defined a neurotransmitter as a “substance that is released at a synapse of by one neuron and that affects another cell, either neuron or effector organ, in a specific manner…”

Put more simply, a neurotransmitter is a chemical that supports the transmission of information between cells (including neurons and glia).

4 Criteria: 

1. Must be synthesized (or stored within a releasing cell. Neurotransmitters can be synthesized in the axon terminal, in the cell body (soma), it can be repackaged after uptake and can be made both pre/postsynaptically on demand. 

2. Must have target sites for endogenous transmitter. In other words, it must have receptors for a naturally occurring transmitter. 

3. The endogenous and the exogenous transmitter must elicit the same response. 

4. Presence of a deactivation mechanism. 

Hope this makes things clearer!


Yeah, big fuckin’ shocker that major imbalances of the most important chemicals in your brain can sorta screw with how it functions and hey just a thought maybe you shouldn’t just refer to having one of many many mental illnesses that are affected by these chemicals as ‘insane’ hm