Point I: No DiscriminationThe term ‘Neurotransmitter’ maybe intimidating but it is important to explore this stereotype. In actual fact, ‘Neurotransmitter’ is just a fancy name for a chemical molecule that is synthesised and functions within the proximity of the brain. It is essentially brain hormone, just like any other hormone in the body. It does not have any special magical power for being in the most complex organ, the brain.
There are still many unknowns within the world of neurotransmitters, like:
- How many different neurotransmitters are there?
- Are all known neurotransmitters fully characterised?- How does neurotransmitters work?
- Why are there so many different neurotransmitters functioning together?
Point II: A Stable PartnershipNeurotransmitters are produced from two main types of cells: Neurons and Glia cells. Neurons are commonly known as brain cells (the main players). However, they cannot function without the help of Glia cells (the supporters). Glia cells feeds and maintain neurons, from the blood supply which the neurons do not have access to. The functionality of the brain is dependent upon these brain cells’ stable partnership.
Point III: The FactoryThe brain works as a network of neurons, which is constantly communicating with one and other. This is how the brain control and regulate our whole biological being. The communication between neurons is based on chemical and electrical signals. The chemical signals are provided by the neurotransmitters, produced by the brain cells.
Point IV: The Delivery ServiceNeurotransmitters are the ultimate messenger of the brain. However, this job is not straight forward. This neuronal network is made up of neurons that are not physically in contact with one another. So, it is not possible for the neurotransmitters to travel fluidly from cell to cell. That is why the electrical signal is equally important. These tiny gaps at the neuronal terminal are known as synapse (Figure 3). The message overcomes this hurdle in a specific manor:
1. Neurotransmitters are grouped together inside a membrane to form a vesicle. This makes a neat and tidy package for delivery (Figure 4).
2. These vesicles get stacked and wait just before the synapse. When the electrical signal arrives, it will trigger the release neurotransmitters into the synapse. (It is OK – don’t panic. This is part of the delivery process).
3. The released neurotransmitters form the chemical signal in the synapse (Figure 5). The neurotransmitter will swim across to the surface of the neighbouring neurons, where there are receptors (life buoys) to note their arrival. [Please note: under no circumstances are any neurotransmitters permitted to enter neighbouring neurons. They will be rescued, biochemically, by their own parental neurons.]
4. The arrival of the chemical signal will in turn trigger the electrical signal. This will then sprint toward the awaiting packages (neurotransmitter-filled vesicles) and push them off the synaptic cliff (release of neurotransmitter). Then the cycle will repeat from one neuron to the next, until the message has reached its destination.
Point V: The Cocktail MixtureThere are a large number of different neurotransmitters. About 50 neurotransmitters have been identified so far. The most commonly known ones are GABA, Histamine, Acetylcholine, Dopamine, Noradrenalin, Endorphins and Substance P.
It is not clear:
i) Why the brain needs so many different neurotransmitter?
ii) How are each neurotransmitter different in function from each other?
Initially, the theory was that a specific neuron was only capable of producing a specific neurotransmitter. Therefore, the outcome function is very rigid and limited. One neurotransmitter is for one type of functional output. This is supported by the vase number of neurotransmitters that has been identified. However, it is unlikely that neurons are only able to function in ~50 different ways. Biochemically, this number is far too small for any biological system.
A more feasible theory is that each neuron produces a cocktail of neurotransmitters. The mix ratio from each neuron is varied, so a different combination of neurons gives a different message for a different function. Just like if each neurotransmitter is a letter of the alphabet, the different combination of letter can form different words to give different meanings.
All in all, the outcome of the neuronal system (Brain) is dictated by the neurotransmitters.
Point VI: Error in the SignalNeurotransmitters have a heavy role in neurological diseases, but very little is known. Since the brain is the most complex organ of the body and it governs all other organ systems. There is no limit to the outcome of any neuronal disorders. However, it can be categories as anatomical deficit (physical/structural damage of neuron) or chemical deficit (lost of chemical signal).
The neurotransmitter’s function has been associated with physical action, thinking, mood and behaviour. The most abundant neurotransmitter is Glutamate, which has been linked with autism, obsessive compulsive disorder (OCD), schizophrenia and depression. This does not suggest that glutamate is the cause of these psychiatric disorders. The pathology is likely to be much more complex because some have these disorders have also been linked to other neurotransmitters as well. Dopamine has been linked to schizophrenia and Attention Deficit Hyperactive Disorder (ADHD). Serotonin has been linked to depression.
This overlap of neurotransmitters and diseases strongly suggest that each neurotransmitter must have more than one functions. The role of these neurotransmitters in psychiatric disorders is unclear. By studying these diseases, it will give clues to the normal neurotransmitters’ function that is lacking.
The mystery that lies within the different neurotransmitters cocktails are waiting to be discovered. The master recipes of these cocktails may be the key to tackling psychiatric disorders and possibly be the cure.