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In pharmacology, an #antidepressant refers to a fairly diverse set of molecules that do not have the same modes of action, the same therapeutic effects or the same undesirable effects.

A common goal: to target monoamines, neuromodulators

Generally speaking, these are molecules that target what are called #neurotransmitters, including serotonin, noradrenaline or dopamine. When a neurotransmitter attaches to receptors in one neuron, it transmits an electrical message that can be transmitted to another neuron. It's kind of like a relay race. There are over 20 different types of synapses, each of which conveys specific messages and are involved in this brain activity differently."

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#Neurotransmitters

The synaptic terminal has these entities here, which are called synaptic vesicles, and they're small, little organelles.

They're little vesicles made of a membrane; just like the cell has a cell membrane, these vesicles have a vesicular membrane.
The neurotransmitters are within the vesicular membrane.

And, the neurotransmitter can be any number of a number of different molecules — #Glutamate, #GABA, #Serotonin, #Dopamine, #Acetylcholine, #Glycine, #Norepinephrine, #Epinephrine, #Histamine, #ATP.

The neurotransmitters are packaged in vesicles. The second thing that's important about this is that we can use the synthesis of a #neurotransmitter as a therapeutic tool.

So, for instance, Dopamine is missing in #ParkinsonsDisease.
It's not that dopamine isn't made per say, that's there's a problem with making it — it's that the cells that make it die.

There's something called 'Mass Effect', which means that you take the starting chemical (the substrate) and then through a series of enzymatic processes reaction, through a series of enzymatic reactions, we end up with a neurotransmitter.

In the case of Dopamine, what we do to treat in most people with Parkinson's is that we give them the substrate — and so that (drug) is what is commonly known as #Sinemet or #Parcopa.

So we flood the system with substrate, and the goal is to get a little bit of that neurotransmitter out of the system.

Image source: https://in.pinterest.com/pin/11962755239342046/?lp=true

**Glial Cells**
The human brain contains 86B neurons and 85B Glia.

**Different types of Glia:**

Astrocytes: Astrocytes are really important type of Glia. They're essentially responsible for keeping the environment clean, they're the sanitation worker of the brain. So they are picking up all the refuse that the neurons have let loose including excess ions, excess #neurotransmitters and their metabolites.

They also are very important during development. They allow neurons to get to where they have to go during development. #Neurons are born in one place and they have to go some place else, and what highway did they take? They hitch on a progenitor cell that is going to become an #Astrocyte.

And, in addition when synapses are formed, the synapses are not maintained without some effort, and part of that is that the synapses are enveloped in the processes of #Astrocytes. So, there's a lot of structural and metabolic support that the Astrocytes are providing for neurons.

Oligodendrocytes and Schwann Cells: The #oligodendrocytes make myelin in the CNS and the #SchwannCells make it in the Peripheral Nervous System. So all these demyelinating diseases will affect either central myelin or peripheral #myelin. They will not affect both -- central or peripheral.

Because they are made by two different types. The Oligodendrocytes in the central nervous system and a Schwann cells in the peripheral nervous system.

Microglia: #Microglia are the one exception to the rule that
nervous system, that the cells of the nervous system come from Ectoderm. These are actually essentially immune cells coming from the blood lineage. These are immune cells that have invaded into the central nervous system and their job is to be quiet. And if we're healthy and everything goes well, they are quiet. But when there is a problem these microglia react, they try to rectify things, they try and bring some attention to areas of damage and what is emerging is that sometimes they go overboard and they start to participate in making the problem as well as solving the problem.