Locus Ceruleus: "Sky-blue place"

You must admit, the name is catchy.

I first read about this spot in the brain in a very entertaining and informative book called Beyond the Zonules of Zinn: a Fantastic Journey Through Your Brain, by David Bainbridge, a vet. I first heard about the book from Ginger Campbell of Brainscience podcast, in Episode 32.

Bainbridge, in his discussion about the tegmentum, has this to say about locus ceruleus;

"Also in this area is the wistful-sounding locus coeruleus, the "sky blue place." Its ethereal blue color probably results from the deposition of long chains of the chemical that its neurons release, norepinephrine. The coeruleus is in no way a restful place, however. It is probably important in driving the rest of your brain to be active when it needs to be, and it is involved in alertness, arousal, stress and ultimately panic. Its neurons send meandering tendrils to almost all other parts of your brain to jolt you into action - for example, it is almost certainly part of the fright-recognition pathway between the hillocks and the almonds. Intriguingly, it is also important in dreaming sleep - something to which we will return briefly in the final chapter of this book. Finally, and perhaps unsurprisingly when you consider what it does, many antidepressants are thought to act on areas with which the locus coeruleus communicates. Maybe depression is when the sky-blue place darkens into twilight."

I must admit I was captivated by the unabashedly poetic way he writes about this "sky-blue place" (along with everything else). He says elsewhere in the book that it was originally discovered and named by Félix Vicq d'Azyr, who was an anatomist, veterinarian, and personal physician to Marie Antoinette.

It sounded like a part that deserved to be checked out more deeply, and I'm glad I did. There are scads of interesting factoids about this brain part, which I will bring here to this blog over the next few days. Meanwhile, here is what is probably its main feature important from a pain perspective: it alerts the whole brain to novel stimuli via ascending (or rostrally projecting) fibers, while simultaneously dampening nociceptive relay neurons in the dorsal horn through descending (or caudally projecting) fibers. (Check out the image provided. Find LC, which is colored lime green in this image, not sky-blue. Trace the arrows projecting from LC. They go up and around the whole cortex, and down to the cord.)



This explains why, even if you have pain, if you were to see a bus coming at your toddler, you forget all about your pain, wouldn't even feel it probably, and would run out to snatch your toddler out of danger.

This makes the locus ceruleus sort of like a transmission that can change gears suddenly, or a switch box that can change the locus of one's attention in a flash. Kandel says (p. 895);

"The largest collection of noradrenergic neurons is in the pons in the locus ceruleus. Remarkably, although the locus ceruleus projects to every major region of the brain and spinal cord, in humans it contains only about 10,000 neurons on each side of the brain. The locus ceruleus maintains vigilance and responsiveness to novel stimuli. It therefore influences both arousal at the level of the forebrain and sensory perception and motor tone in the brain stem and spinal cord."

From the Encyclopedia, p. 639 Vol 3;

"LC activation can also produce potent anti-nociception by reducing the response of neurons of the dorsal horn of the spinal cord through the stimulation of α2- adrenergic receptors."

References:
1. Handbook of Clinical Neurology: The Autonomic Nervous System Part I, Elsevier 2000, Appenzeller O., Vinken PJ, Bruyn GW
2. Gray's Anatomy (39th ed)
3. Encyclopedia of the Human Brain
4. Principles of Neural Science 4th Ed (Eric Kandel)
5. Image provided courtesy of CNSforum Brain Explorer image bank

Additional reading:
1. Brainstem (Scholarpedia)