Happy holidays from the BrainWaves team! To celebrate this American family pastime, we will be taking a step back to critically evaluate the dishes typically served at a Thanksgiving feast. Specifically, how the dishes that may impact the central nervous system.
This week’s episode features Dr. Jason Maley, a friend of mine all the way back from medical school at Tulane University.
Dr. Jason Maley scrutinizing an apple at a local orchard. The episode opens with a general discussion on standard safety measures to prevent commonly acquired infectious diseases–in particular, those transmitted via the fecal-oral route. While this mode of pathogen acquisition is crucial to the transmission of your standard toxin and bacterial exposures (e.g., S. aureus and E. coli), Dr. Maley hones in on the neurologic complications of fecal-oral contamination. As an example, consider botulism. In particular, there are two forms of botulism which come to mind: infant botulism (where the Clostridium botulinum spores contaminate and reproduce in an infant’s unexposed and incompletely colonized gut) and foodborne botulism (where the C. botulinum toxin is ingested in adults, causing similar symptoms of a descending paralysis). The toxin itself acts by disrupting the SNARE proteins at the presynaptic terminal of neuromuscular junctions, thereby impeding release of acetylcholine–effectively paralyzing muscles. Foodborne botulism is relatively rare in the US these days, with fewer than a hundred cases reported annually. But you don’t want this to ruin your holiday season, so be aware of the home canned goods and other non-commercial foodstuffs that serve as a vehicle of this infectious agent.
Almost equally uncommon but just as deadly, contamination of soft cheeses and recently hummus and Blue Bell ice cream with Listeria monocytogenes can make a mess of your nervous system. In the nervous system, listeria typically causes a meningitis, with or without encephalitis, and brain or spinal cord abscess. However, most neurologists package it in their differential diagnosis of rhombencephalitis, with subacute cranial neuropathies, cerebellar ataxia and weakness or numbness.
Moving along with the infection theme, Dr. Maley also discusses a particular microbe that is found in pork products–Taenia solium. The agent responsible for neurocysticercosis, T. solium is also acquired via the fecal-oral route between humans. Although pigs technically act as intermediate hosts for viable cysticerci (see image to the left), evidence suggests that the more common mode of transmission is person-to-person. An asymptomatic carrier of taeniasis will excrete eggs of the adult taenia spp. and once these are ingested, the eggs will hatch into embryos (a.k.a., oncospheres) which actively cross the intestinal lumen and spread to areas supplied by the circulatory system–like the muscles, the eye, and the brain. [Note the oxford comma here. Eye and brain are NOT muscles.]
But this episode does not focus entirely on infections of the central nervous system. Next we discuss the controversial nature of tryptophan in causing lethargy. Yes, turkeys contain whopping doses of this amino acid which some scientists have postulated may be responsible for your food coma. But other commonly eaten foods like chicken, milk, and tuna have similar concentrations of this protein building block. And more importantly, from a brain perspective, it’s actually the ratio of tryptophan to other competing amino acids that may be important in increasing the levels of serotonin and melatonin in the nervous system (hormones that make you sleepy).
And of course we couldn’t do justice to our listeners without recognizing the role of alcohol as part of the Thanksgiving feast. I’m not going to bore you with the details here, but if you want to hear more about the pleiotropic effects of this neurotoxin AND neuroprotectant, you should take a few minutes during the holiday festivities to check out the podcast. I guarantee you’ll learn something new in it!
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