Chapter 5 neuro, this will be the first of three videos focused on different
classes of antidepressants. This video will focus on the four different classes
of antidepressants that we see in practice
and how they work. Depression is thought to be due to a decreased amount of neurotransmitters in the brain, especially
serotonin, which we think of as a feel-good
neurotransmitter, or other things like norepinephrine and dopamine. It's thought that by increasing the levels of these neurotransmitters,
we can then in turn enhance our mood and improve our depression.
Here is just a list of the four classes that we will review today.
The first class is selective serotonin reuptake inhibitors or SSRIs,
and the example we will be looking at today is fluoxetine or Prozac. This drug just works to
inhibit the breakdown of serotonin within the neurons to therefore increase the level of serotonin in the brain.
The next class is
serotonin norepinephrine reuptake inhibitors or SNRIs. This isn't to be confused with SSRIs.
In SSRI, the first 'S' stands for selective and in SNRI, the
'S' does not stand for selective - it stands for serotonin. SNRIs work to inhibit the breakdown of both serotonin and norepinephrine.
The example we'll work with today is venlafaxine or the brand name Effexor.
The next class is tricyclic antidepressants or TCAs.
They work the same way that SNRIs work by inhibiting the reuptake of serotonin and norepinephrine,
but they're named after their shape, which is the 3-ring structure that we see with tricyclic.
Monoamine oxidase inhibitors, those are the MAOIs, and the example
we'll use today is isocarboxazid or Marplan. They work on monoamine oxidase,
which is an enzyme in the brain that breaks down
neurotransmitters like serotonin, norepinephrine and dopamine.
If we inhibit this enzyme, we increase the levels of those neurotransmitters to treat depression.
Let's look at an example. Question one will be a select all that apply. 'An antidepressant that works on serotonin
and norepinephrine is?'
So we have the SSRI, SNRI, TCA and MAOI.
The correct answer is B),
C) and D). SNRIs, like we said before, work on both so serotonin and norepinephrine,
and so do TCAs like amitriptyline. The MAOIs also works on dopamine.
The selective serotonin reuptake inhibitors like fluoxetine work on serotonin only.
The next class or the next question: 'An antidepressant that works on serotonin and norepinephrine
and is named after its shape is?' and again, we have the same four options for our answer.
The correct answer is C) amitriptyline. That one works on both
serotonin and norepinephrine
and is named after its shape which has the three cyclic rings. A)
Is incorrect because it only works on serotonin, B) venlafaxine is incorrect, it does work on serotonin and norepinephrine
but it's not named after its shape, and D) isocarboxazid is incorrect because it works on the monoamine oxidase
enzyme.
The next couple questions will change the question to make each of the answers correct.
'An antidepressant that works only on
serotonin?' The correct answer is A) fluoxetine. That one is selective for serotonin as the name implies.
B) and C) are incorrect because they work on serotonin and norepinephrine.
Isocarboxazid
works a little differently as it blocks that monoamine oxidase enzyme which then in turn
causes it to work on serotonin, norepinephrine, and dopamine.
Okay, so now we're going to make B) correct. 'An antidepressant that is an SNIR is?'
B) venlafaxine.
As we reviewed before, fluoxetine is an SSRI,
only inhibiting serotonin.
Amitriptyline does work in the same way that SNRIs do but they're named after their shape.
Isocarboxazid is an MAOI.
Okay, so now we'll make D) correct. 'An antidepressant that prevents the breakdown of neurotransmitters is?' D) isocarboxazid.
A) B) and C) are incorrect because those are all reuptake inhibitors,
so they just prevent the breakdown of the neurotransmitters, but theisocarboxazid works by
inhibiting
monoamine oxidase which usually breaks down neurotransmitters, so by inhibiting the effect of the monoamine oxidase
enzyme, we are able to then in turn increase levels of neurotransmitters like serotonin,
norepinephrine and dopamine