Chapter 7: Treatments for Mood Disorders: So-Called "Antidepressants" and "Mood Stabilizers"

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Welcome back to the Deep Dive.

Today we are getting into a really massive topic, the pharmacological treatments for mood disorders.

Right, we're talking depression,

mania, those tricky mixed states.

And we've gone through the sources with a very specific mission in mind.

We want to move past those confusing clinical labels, you know, antidepressants, mood stabilizers.

They're becoming archaic, really.

Exactly.

And instead, we're focusing exclusively on the core science, the drug's actual mechanism of action.

It's a huge conceptual shift, but it's so necessary.

The research is clear that we need to adopt a neuroscience based way of talking about this.

We should be categorizing these agents by how they work.

So whether they block a transporter or hit a receptor or something else entirely.

Precisely.

It's about precision.

Stop naming a treatment after the disease and start naming it after its mechanism.

Okay, I love that.

It clears things up immediately.

But before we dive into the chemistry, let's make sure we're all using the same language for success.

The clinical vocabulary, yeah.

Right.

So when a medication is starting to work, the first term we use is response.

What does that mean exactly?

Response is pretty straightforward.

It just means the patient has had at least a 50 % reduction in their symptoms.

50%.

And that used to be the main goal.

But things have gotten much more rigorous now.

The modern goal is remission.

And remission is total symptom relief.

Essentially, yes.

The complete removal of pretty much all symptoms.

And if you can sustain that remission for several months, say six months,

we then call that recovery.

Got it.

And because depression so often comes back, we have terms for that too.

A relapse is when symptoms return before a patient hits that full recovery mark.

And a recurrence is when it comes back after they've been in recovery for a good while.

Okay, that's our framework.

So let's get into it starting with, the hard truth about the foundational drugs for unipolar depression.

And it is a hard truth.

The efficacy baseline is frankly pretty sobering.

For the classic monolamine reuptake blockers, your SSRIs, your SNRIs, only about one third of patients with unipolar depression get to true remission on their first try.

One third.

Wow.

For drugs that have been the gold standard for decades, that number feels surprisingly low.

It is.

And the returns diminish fast.

Even if you do everything by the book, four different treatments, 12 weeks each, over a whole year, you still only get about two thirds of patients to remission.

Which explains why we need to have this conversation.

We need better tools.

We do.

So that leaves a huge number of people in that frustrating middle ground, you know, response, but not remission.

What are the issues?

We're talking insomnia,

just overwhelming fatigue, trouble concentrating, that kind of mental fog.

And the lack of interest, that anhedonia.

Yes.

And crucially, what often gets missed are the painful physical complaints.

They're incredibly common residual symptoms.

And what's so fascinating is what doesn't usually stick around.

The sources point out that core depressed mood and suicidal thoughts are actually the least common residual symptoms.

Right.

Which suggests the drug is working on that deep existential dread, but it's leading behind this physical and mental sludge.

Which is why we have to move beyond single mechanism drugs.

But first, let's master the original, the SSRIs.

The mechanism isn't instant, right?

There's this whole cascade.

Five part cascade, yeah.

And it perfectly explains that two to four week delay that could be so confusing for patients.

Okay, walk us through it.

Let's visualize that serotonin neuron.

Part one, you take an SSRI and it immediately blocks the serotonin transporter, or SIRT.

And that's happening everywhere on the neuron.

Both at the axon terminal and up near the cell body in what's called the somatodendritic area.

Part two, serotonin levels, 5 -HT, they shoot up right away, but only in that area near the cell body.

And that surge of serotonin stimulates these things called presynaptic 5 -HT1A auto receptors.

So these auto receptors are like a brake pedal.

They sense all this new 5 -HT and tell the neuron, hey, whoa, slow down.

That's the perfect analogy.

They are hitting the brake, which suppresses the release of 5 -HT everywhere else in the brain.

And that's why you don't feel better right away.

I might even feel a bit more agitated at first.

It can happen.

So part three,

over a few weeks, the constant stimulation forces those auto receptors to give up.

They desensitize or downregulate.

The brake pedal basically gets worn out.

It gets worn out.

Exactly.

And that's part four.

Once the brake is disabled, the neuron is disinhibited.

It turns on and you get this massive sustained release of 5 -HT across the entire brain.

And that delayed flood of serotonin is the therapeutic moment.

That's when people start to feel better.

And finally, part five, all that extra 5 -HT starts to desensitize the postsynaptic receptors, which is what we think correlates with building a tolerance to some of those initial side effects like nausea.

It's such a complex, elegant sequence, but it definitely requires patience.

It does.

And while that cascade is common to all SSRIs, this is where it gets interesting because they are definitely not all the same.

They're, you know, not so selective.

Okay, let's get into that.

What about floxatine?

It's known for having 5 -HT2C antagonism.

Why does that matter?

So blocking the 5 -HT2C receptor is like removing another natural brake, but this one is on norepinephrine and dopamine.

Ah, so you get a secondary activating effect.

Exactly.

It can feel more energizing, which might explain why it's used for conditions like bulimia.

Then there's sertraline.

It has weak dopamine transporter, or D8 inhibition, and also the sigma -1 binding.

What's the sigma -1 part about?

Well, the D8 inhibition gives it a little dopamine kick, which can help with energy and motivation.

The sigma -1 binding, it's less understood, but it seems to be involved in protecting neurons.

It just gives it a slightly broader profile.

And on the flip side, you have peroxetine, which is known for being more calming, almost sedating.

Right, because it has muscarinic anti -cholinergic action.

Yeah.

But the thing to watch with peroxetine is its inhibition of nitric oxide synthase, or NA.

And that's the mechanism linked to sexual dysfunction, right?

It is.

NAAS is critical for that physiological process, so inhibiting it is a big deal for a lot of patients.

It's also known for having some of the worst withdrawal if it's stopped suddenly.

Good to know.

And we have to mention esitalopram.

Ah, yes.

The quintessential SSRI.

It's the pure S enantiomer, which just means it has the cleanest, most targeted CERT inhibition without all those messy secondary properties.

So moving beyond these, the fact that so many people don't remit on the first try really pushed pharmacology to get more creative.

Absolutely.

We had to start hitting multiple targets at once.

Which brings us to the dual and multi -action drugs.

First up are the sparris, like villazodone.

This is a really clever design.

It combines that CERT inhibition with instant 5 -HT1A partial agonism.

Okay, so instead of waiting weeks for the break pedal, the 5 -HT1A auto receptor, to wear out, this drug just goes and partially pushes it from day one.

That's it, exactly.

It acts like an artificial serotonin at that key spot, potentially speeding up the whole process.

And maybe even reducing some of those

Very cool.

And then we have the classic SNRIs, the serotonin norepinephrine reuptake inhibitors.

The sources describe them as having two and a half mechanisms.

I love that.

It's a great way to think about it.

So they boost 5 -HT and NE everywhere.

That's the two.

The crucial half action is that they also boost dopamine, but only in the prefrontal cortex.

How does that work?

How does blocking norepinephrine transporters boost dopamine?

It's this beautiful quirk of neuroscience.

The PFC, the prefrontal cortex, is special.

It doesn't really have dopamine transporters.

So any dopamine that gets released there is actually cleaned up by the norepinephrine transporter, the NET.

So if you block NET, you're doing double duty in the PFC.

You boost NE and you boost DA.

Which is perfect for targeting that cognitive fog and lack of focus.

And this is why a major SNRI like deloxetine has such strong data for treating painful physical symptoms.

It validates this idea that somatic pain is a real part of depression, these dual action drugs can actually target.

Okay, so now let's go completely off the reuptake map.

Let's talk about mirtazapine, a NASA.

Right.

It doesn't block any monoamine transporter.

Its main antidepressant action is from alpha -2 antagonism.

So if the alpha -2 autoreceptor is the brake cable for releasing both NE and 5 -HT, mirtazapine just comes in and cuts the cable.

That's it.

You cut the brake, you get this powerful disinhibition, a huge simultaneous surge of both NE and 5 -HT.

It's a completely different way to get a dual monoamine boost.

Fascinating.

And then there are drugs that act differently depending on the dose, like trazodone.

Yeah, a seri.

At low doses, trazodone is basically just a sleeping pill.

It's a hypnotic.

It binds really tightly to its highest affinity receptors, H1, 5 -HT2A, and alpha -1, which are all involved in sedation.

But to get a real antidepressant effect, you have to go to much higher doses.

So you can recruit its other lower affinity target.

Exactly.

That's when you start getting CERT inhibition and other effects that actually treat the depression itself.

And finally, in this category, there's the multimodal agent vortioxetine.

It seems to have a unique pro -cognitive benefit.

It does.

It shows superior performance on processing speed tests.

And its mechanism is, well, it's a symphony.

It hits CERT, 5 -HT1A, 5 -HT3, 5 -HT7, and more.

So all that synergistic action ends up boosting what?

It enhances the release of four key neurotransmitters for cognition.

5 -HT, dopamine, norepinephrine, and crucially, acetylcholine.

It's a direct assault on that cognitive fog.

Okay, let's pivot to something really exciting, the rapid onset mechanism.

Starting with neuroactive steroids like brixanolone for postpartum depression.

This is totally outside the monoamine world.

Completely.

This drug binds to a very specific site on GABA receptors.

But importantly, it targets the extra synaptic GABA receptors, which benzodiazepines don't really touch.

And the thinking is that depression, especially postpartum, might involve a GABA deficiency.

That's a leading theory.

So this mechanism directly compensates for that, which could be why it brings such rapid relief to patients who are in crisis.

And speaking of rapid relief, the ultimate example has to be ketamine.

How does it work so fast?

We're talking minutes, not weeks.

It's a total paradigm shift.

We're moving from chemical balance to structural change.

Ketamine blocks NMDA receptors.

But the key is where?

It blossoms on inhibitory GABA inner neurons.

Okay, so it blocks the inhibitor.

Yes.

You get disinhibition.

You release the break on glutamate, which leads to this immediate powerful burst of glutamate release.

And that flood of glutamate is what causes the antidepressant effect.

That glutamate burst stimulates a different receptor, the AMPA receptor.

This triggers a whole intracellular cascade that within hours releases growth factors like BDNF.

Brain -derived neurotrophic factor.

Right.

And that leads to the rapid formation of new dendritic spines.

It's called synaptogenesis.

We're not just rebalancing chemicals.

We are literally regrowing and repairing neuronal connections in a matter of hours.

That's just astounding, truly.

Okay, let's switch gears to bipolar disorder and the controversial term mood stabilizer.

Yeah, it's a label label, as the source puts it.

The problem is some of these drugs are mania -minded, treating symptoms from above the baseline.

While others are depression -minded, treating them from below.

Exactly.

The classic antiemannic is lithium.

Its mechanism is still a bit of a mystery, but it works.

The big takeaway clinically is its narrow therapeutic window.

You have to monitor it closely.

Then you have the anticonvulsants, valproic acid and carbamazepine, which are more mania -minded.

Right.

They work mainly by blocking voltage -sensitive sodium channels.

Which basically just calms down the firing of the neurons.

It dampens excessive neuronal firing, yeah.

It reduces that overblown neurotransmission you see in mania.

And contrast that with lamotrigine, which is considered depression -minded.

It's used to prevent recurrence.

And its unique mechanism is that it reduces the release of the excitatory neurotransmitter, glutamine.

It's great for preventing bipolar depression, but not so much for treating acute mania.

Which brings us to a huge clinical shift.

The first -line treatment for bipolar depression is often not a classic antidepressant anymore.

That's right.

It's increasingly a serotonin -dopamine blocker.

Things like quetapine, loracidone.

Why the change?

Because traditional SSRIs just don't work that well in bipolar depression.

And, more importantly, they carry a real risk of flipping someone into mania or a mixed state.

Okay, let's spend a minute on a newer agent, caraprazine.

It's approved for both mania and depression.

And what sets it apart is its potent D3 partial agonism.

What does the D3 receptor do?

The D3 receptors, specifically in the VTA, act as an auto -receptor break on dopamine release, particularly to the pre -funnel cortex.

Another break pedal.

Another break pedal.

And caraprazine, as a partial agonist, blocks that break without fully stimulating it.

So you get that same disinhibition we talked about.

So it's releasing the break on dopamine delivery to the PFC.

And what does that help with?

That boost in PFC dopamine is thought to directly target those really tough symptoms.

Yeah.

Low motivation, anhedonia, cognitive issues.

It's a very precise modulation.

Okay, finally, let's touch on what we do for treatment resistance.

Augmentation strategies.

The goal is almost always to get all three monoanes involved.

You see triple action combos like an SSRI plus propropion to add in dopamine.

And the one with the best name,

California rocket fuel.

Right.

An SNRI combined with mirtazapine.

You're combining reuptake blockade with

mirtazapine's powerful disinhibition from alpha -2 antagonism.

You're hitting the gas and cutting multiple breaks at the same time.

It's a theoretical quadruple boost of both NE and 5 -HT.

And looking to the future, we're seeing more rapid action agents.

There's an oral NMDA antagonist now, dextromethorphanpropion.

Yeah, the dextromethorphan is the NMDA antagonist, like ketamine.

And the propropion is just there to inhibit the enzyme that breaks it down so it sticks around long enough to work.

And then there's the whole frontier of hallucinogen assisted psychotherapy.

Right.

Using 5 -HT to a agonist like psilocybin.

The theory is that they help you re -experience difficult memories in a therapeutic setting, which then allows you to disrupt the emotional coding of that memory.

So after all of this, what does it all mean for you, the listener?

I think it's that the future is less about finding a single magic bullet for a disease.

And much more about crafting a precise portfolio of mechanisms.

Exactly.

Using transport blockers, receptor antagonists, all these tools to tailor a treatment that achieves total remission, especially for those stubborn cognitive and physical symptoms.

The clinical implication is just profound.

The breakthroughs aren't just coming from monoamines anymore.

Understanding D3 antagonism, or rapid synaptogenesis from ketamine, it tells us the next big steps will be in fine -tuning these other systems to hit the symptoms the classic drugs miss.

We really hope this knowledge helps you connect the dots between the pharmacology and the clinical reality, giving you a mechanism -first way to think about these crucial treatments.

Thank you so much for joining us for this deep dive.

And continue exploring these complex interactions.

There is still so much more to discover in the next generation of these treasons.