Myth: Substance X MUST cross the blood brain barrier to affect the brain.
Myth Debunked: Substance X affects a peripheral system that directly affects a central system. Read on for details!
Let's put this nootropic community myth to rest once and for all, shall we! =) (btw, I know that many of you already know that this is a myth)
Question: Can supplements/drugs that DO NOT cross the blood brain barrier affect learning and memory in the central nervous system?
Answer: Yes, yes, a million times yes. =)
How? Peripheral epinephrine (which does not easily cross the BBB) affects the vagus nerve; the vagus nerve causes the amygdala to release norepinephrine into the central nervous system.
http://www.ncbi.nlm....les/PMC3384987/
"...epinephrine does not gain access to the CNS due to the restrictive properties of the blood-brain barrier (BBB)."
"The results from Experiment 1 demonstrated that increasing neural transmission along ascending vagal fibers following learning produces a significant and long lasting improvement in memory for emotional experiences."
"The results from Experiment 2 demonstrated that epinephrine increases firing discharge along afferent fibers of the vagus nerve and this change persisted for up to one hour post-injection. The epinephrine-induced increase in vagal firing was accompanied by significant elevations in extracellular concentrations of norepinephrine in the basolateral amygdala that remained high for up to 120 min post-injection."
"Findings emerging from the final study reveal that systemic epinephrine injection and VNS induce similar patterns of neuronal activation within brain regions associated with memory."
"In conclusion, the collective findings demonstrate an integral role of epinephrine and the vagus nerve in influencing central noradrenergic systems ascribed a role in processing memory for emotionally arousing experiences."
More Random Quotes from the Study: (just to hammer the nails in this coffin)
"Our findings indicate that treatments that raise circulating levels of epinephrine in the periphery or increase discharge along ascending fibers of the vagus nerve produce similar changes in the expression of Fos proteins in noradrenergic neurons in the NTS, LC, VLM, and their areas of termination."
"The results show that central noradrenergic nuclei represent a primary target of peripheral systems that are engaged by exposure to emotionally arousing events."
"In turn, activation of noradrenergic release in each of the limbic circuits identified in this study constitutes areas wherein the beneficial effects of heightened levels of arousal in the periphery influence the effective storage of events into memory."
"Significant increases in cerebral blood flow after acute left vagal stimulation was noted bilaterally in the hippocampus, amygdala, orbitofrontal gyri, cingulate, thalami, hypothalami, and the anterior insula."
"...changes observed after vagal stimulation in a fMRI study of patients with intractable depression involved increased blood oxygenation level in bilateral orbitofrontal and parieto-occipital cortex, left temporal cortex, amygdala, and the hypothalamus."
"...VNS-induced activation was detected in bilateral thalamus, insular cortices, postcentral gyri and inferomedial occipital gyri, left basal ganglia, and right posterior superior temporal gyrus."
"...experiments suggest that epinephrine's actions on memory and in potentiating norepinephrine output in the amygdala may be mediated by the initial activation of peripheral vagal fibers that project to the brain."
"The projection of vagal afferents to the NTS is important in understanding how vagal activation may affect distinct neuronal circuits to regulate norepinephrine release in the amygdala."
"For instance, ascending fibers of the vagus synapse on the A2 norepineprhine-containing neurons in the NTS (Sumal et al., 1983) that course through the brainstem to innervate and release norepinephrine in the amygdala."
"A2 neurons in the NTS also project directly to locus coeruleus neurons (LC; Van Bockstaele et al., 1999) that provide the major source of noradrenergic innervation to the basolateral amygdala."
"...electrical stimulation of ascending vagal fibers or epinephrine injection alone, produces significant and long lasting increases in amygdala norepinephrine levels that are attenuated by inactivating the site of termination of vagal axons in the brainstem, the NTS."
"Thus, vagal activation in response to epinephrine secretion may represent one mechanism by which emotionally arousing events facilitate memory processing by initiating norepinephrine release in the amygdala."
"...peripheral levels of epinephrine affect vagal nerve discharge and the subsequent potentiation of norepinephrine release in the basolateral amygdala."
"Findings emerging from this collection of studies establish the importance of ascending fibers of the vagus nerve as an essential pathway for conveying the peripheral consequences of physiological arousal on brain systems that encode new information into memory storage."
"Findings from this series of studies reveal an integral relationship between the arousal related hormone epinephrine and ascending fibers of the vagus nerve in influencing memory processing through interactions with central noradrenergic systems."
Edited by lostfalco, 31 August 2015 - 03:40 AM.