When I was fifteen years old, on a muggy May Wednesday in Pittsburgh, I learned about the blood-brain barrier.
Before, through prematurely-peeled scabs and too-loose molars and over-chewed hang-nails of third grade, I had come to know my sloshing erythrocytes and leukocytes and pulsating plasma as ubiquitous. Ubiquitous as the ubiquitin enzymes that nonchalantly whirl and twirl through my cells. Blood was a chartreuse reservoir, a watershed, upon which my flesh delicately floated. Under my skin, blood was everywhere. Or, so I thought.
The blood-brain barrier is a humble thing. A forgotten thing. Or, rather, a thing never realized. It is a diaphanous layer of endothelial cells that guards brain cells from blood vessels (Abbot et al 2006). I thought that blood cells could travel anywhere they wished in my body, on miniature turnpikes to junctions to trails and to other cells. But they can’t. They can’t travel to my cerebral cortex. To my brain. To me.
Blood and most of its cumbersome cargo can’t saunter through the kingdom of spongy grey and tangled white matter. But, some cargo can. VIP cargo can. Glucose— tiny nuggets of chemical energy—can. Energy is life, so energy can travel fast past the toll-collector; it has an E-Z Pass on the Pennsylvania turnpike.
Cantaloupe-hued sticky-monkey blossoms and Santa Cruz Mountain ponderosa puzzle-bark and Mono Lake tufa crumbs. Gulps of zooplankton and Asilomar turban snail poop and Carmel Point sunsets and sand-encrusted, stale pastries. Warm whispers of Mom’s soft voice reading Siddhartha to the family from the other tent. Adrenaline-squirting phantoms of mountain-lion cubs in Tuolumne Meadows and back-country vegetarian chili.
These are the things which can cross my blood-brain barrier. These are the things which bear E-Z Passes on the Pennsylvania turnpike. These are the things that are glucose; these are the things that are energy. These are the things that are life. These are the things that can travel fast past the toll-collector, as if blessed with some hereditary familiarity.
Stands of New Hampshire white pines and honey-hued birch and melting mounds of snow. Horseshoe crabs and warm Atlantic breezes. West Texan chaparral and itinerant termites of the semi-arid Llano Estacado. Crispy South Dakotan Badlands.
These are the things which cannot cross my blood-brain barrier. Between me and these zany natural places far from home is a barrier almost as tangible as the gauzy endothelial cells in my brain. I didn’t usher in mitosis, but the cells have proliferated nonetheless. To know by feeling is not easy for me, but this, I know by feeling…
When I sit amid sleepy, wave-misted Monterey Pines and granite alcoves at Point Lobos, the forest is soluble in me. Or, rather, I am soluble in the forest. The Monterey Pines dissolve into me, and I dissolve into the Monterey Pines. When I sit among thickets of Witch Hazel and Hemlock in the Academy Woods, or under the shade of a willow in Pennsylvania, the forest is not soluble in me, and I am not soluble in the forest. I wish I could say it were, and I wish I could say I were, but it is not, and I am not.
I first learned about the blood-brain barrier at the International Science Fair. But perhaps, I’d known about it much earlier than that. Or perhaps, I’d felt it much earlier than that. I’d felt it the first time I sat in unknown forests under unknown trees under the unknown auspices of unknown clouds over my head.
Part of me wishes it would melt away, that the endothelial cells will pop quietly in apoptosis, that I could be soluble in the unfamiliar, and that the unfamiliar could be soluble in me.
But part of me knows, in some private crevice in the skull, that the blood-brain barrier is, on most days, my only tether to home. It may be diaphanous and it may be humble, but it links my internal core—my brain—to my external core—California, and its mountains and deserts and delectable dirt and rabid waves. To the glucose that sustains my spirit. It deserves some respect. Not apoptosis.
Abbott, N. Joan, Lars Rönnbäck, and Elisabeth Hansson. “Astrocyte–endothelial Interactions at the Blood–brain Barrier.” Nature Reviews Neuroscience 7.1 (2006): 41-53. Web.