The doctor reviewed the causes of heart valve disease as well as prevention tips, but she knew he wasn’t listening. He had valve replacement surgery six months later. Causes of a disease are important — one of the reasons why we’re discussing the kynurenine pathway and depression.
Traditionally, then, serotonin and all that comes with it were the scene of the MDD action. You know, the “happy hormone” bit.
Introduction
My emotional and mental illnesses went full throttle when I was 20-years-old — 52 years ago. For the sake of “we’re in the same boat” possibilities, my diagnostic history includes panic disorder with agoraphobia, substance use disorder, generalized anxiety disorder, and obsessive-compulsive disorder.
Now, my disorder experience may have begun 52 years ago, but between being shell-shocked, clueless, and denial-ridden, the legit recovery wheels didn’t begin to turn until I was 30 — 42 years ago.
All in
I was 100% into it, wanting to learn everything I could about what I was experiencing. And I was especially interested in causes — there was comfort and security in knowing the “Why’s” of it all. I mean, I had no idea what to do about my misery, but at least I’d partially understand what was going on in my brain and the rest of my body.
The kynurenine pathway and depression: Cause and effect
In our neck of the woods, knowledge is true power — to learn, heal, and help others do likewise.
I had a thirst for knowledge in those days, which continues. I’m always on the lookout for interesting and helpful information. Sure, it’s for Chipur readers, but it’s also for me.
Here’s a prime example…
The article I published last week, “Are antidepressants bad for you? 10 deceiving claims,” was based on the work of two prominent psychiatrists. I included what they had to say in response to a deceiving claim about antidepressants…
“…depression is often determined by a myriad of biopsychosocial causes. As a recent comprehensive review concluded, the determinants of depression include ‘…the microbiome, dysregulation of the hypothalamic-pituitary-adrenal axis, inflammatory reactions, the kynurenine pathway, as well as psychological and social factors.”
Wait, the “kynurenine pathway?” Apparently, it’s important, but I’d never heard of it. So I made it my business to learn about it — for your potential needs and mine.
As long as we’re there, let’s talk about it…
The kynurenine pathway
To learn about the kynurenine pathway (KP), I turned to a paper I bumped into online: “Kynurenine pathway dysregulation in major depressive disorder: the convergence of excitotoxicity, neuroinflammation, and oxidative stress.”
Dated February 26, 2026, and written by Grace O’Regan, Zoe Plummer, Brian R Christie, Sandy R Shultz, and Josh Allen, it was published in the Journal of Neuroinflammation.
Traditionally
The authors begin by pointing out that major depressive disorder (MDD) has traditionally been linked to deficient serotonergic (liberating, activated by, or involving serotonin in the transmission of nerve impulses) neurotransmission, chronic stress, and heightened inflammation. Traditionally, then, serotonin and all that comes with it were the scene of the MDD action. You know, the “happy hormone” bit.
Before we move on, let’s take a quick look at tryptophan.
Tryptophan
For those who don’t know, tryptophan is…
An essential (not produced in the body) amino acid crucial to the functioning of many of our organs and systems.
When we ingest tryptophan from animals or plants, our body absorbs it and converts it into the hormone and neurotransmitter serotonin. As you may know, serotonin drives numerous vital bodily functions and systems — including mood, digestion, sleep, bone health, and sexual health.
A new scene
Okay, we’re back. Bringing things to the present, it seems another scene of MDD action needs to be considered and explored. The authors state that compelling evidence shows that under conditions of chronic stress or systemic inflammation, the KP causes a number of enzymes to be upregulated, diverting metabolism away from the manufacture of serotonin. The result are profound consequences for both peripheral physiology and central nervous system (CNS) function.
What’s the point?
All these words and the biochemistry have to serve some purpose — right?
I just dropped 800+ words on you — some of them heavy on the biochemical side of the fence. Understandably, you may be thinking “Okay, Bill, what’s your point?
Here are four of them…
- The kynurenine pathway is fascinating and yet another example of the wonders of the human body;
- For years, major depressive disorder has been linked to deficient serotonin neurotransmission, chronic stress, and heightened inflammation. Now, a new player, the kynurenine pathway, is the center of attention. Chronic stress and heightened inflammation continue to be factors.
- it’s comforting to know that research is ongoing in the effort to effectively manage major depressive disorder.
- It’s good to have a thirst for knowledge — intentionally researching things and bumping into them, like how I found the kynurenine pathway,
And you know what? That’ll do it.
If you’d like to review the Journal of Neuroinflammation paper, you can access it through Springer Nature Link:: “Kynurenine pathway dysregulation in major depressive disorder: the convergence of excitotoxicity, neuroinflammation, and oxidative stress”
Please review the Chipur emotional and mental illness info and inspiration titles on the articles page — or by category below, right sidebar on desktop. We’ll both appreciate it.
After a decades-long wrestling match with emotional and mental illness, Bill finally found his professional and personal passion – life’s meaning. He wanted to lend a hand to those struggling as he did, so off he went to grad school at age 49 and earned his counseling credentials. He continues his service through Chipur and other projects.