A personal collection of my favourite science-related articles, pictures, notes, etc. Enjoy :)
Our Three (Brain) Mothers
Protecting our brain and central nervous system are the meninges, derived from the Greek term for “membrane”. You may have heard of meningitis - this is when the innermost layer of the meninges swells, often due to infection, and can cause nerve or brain damage, and sometimes death.
There are three meningeal layers: the dura mater, arachnoid mater, and pia mater. In Latin, “mater” means “mother”. The term comes from the enveloping nature of these membranes, but we later learned how apt it was, because of how protective and essential the meningeal layers are.
- The dura mater is the outermost and toughest membrane. Its name means “tough mother”.
The dura is most important for keeping cerebrospinal fluid where it belongs, and for allowing the safe transport of blood to and from the brain. This layer is also water-tight - if it weren’t, our cerebrospinal fluid (CSF) would leak out, and our central nervous system would have no cushion! Its leathery qualities mean that even when the skull is broken, more often than not, the dura (and the brain it encases) is not punctured.
- The arachnoid mater is the middle membrane. Its name means "spider-like mother", because of its web-like nature.
The arachnoid is attached directly to the deep side of the dura, and has small protrusions into the sinuses within the dura, which allows for CSF to return to the bloodstream and not become stagnant. It also has very fine, web-like projections downward, which attach to the pia mater. However, it doesn’t contact the pia mater in the same way as the dura: the CSF flows between the two meningeal layers, in the subarachnoid space. The major superficial blood vessels are on top of the arachnoid, and below the dura.
- Pia mater is the innermost membrane, which follows the folds (sulci) of the brain and spinal cord most closely. Its name means “tender mother”.
The pia is what makes sure the CSF stays between the meninges, and doesn’t just get absorbed into the brain or spinal cord. It also allows for new CSF from the ventricles to be shunted into the subarachnoid space, and provides pathways for blood vessels to nourish the brain. While the pia mater is very thin, it is water-tight, just like the dura mater. The pia is also the primary blood-brain barrier, making sure that no plasma proteins or organic molecules penetrate into the CSF.
Because of this barrier, medications which need to reach the brain or meninges must be administered directly into the CSF.
Anatomy: Practical and Surgical. Henry Gray, 1909.
Bismuth is the heaviest nonradioactive element and is essentially a nontoxic neighbor of lead and thallium in the periodic table. It is mined as bismuth oxide (Bi2O3, also known as bismite) or bismuth sulfide (Bi2S3, bismuthinite), and the brittle, silvery elemental form is one of a few substances (water is another) for which the solid is less dense than the liquid. Although bismuth has been extensively used in alloys, pharmaceuticals, electronics, cosmetics, pigments, and organic, the chemistry of bismuth is perhaps the least well established of the group-15 elements (known as the pnictogens). Compounds of bismuth typically have low solubility in most solvents, so that definitive formula assignments are usually based on X-ray diffraction studies of crystalline samples that have been isolated in small or indefinite quantities. Most isolated compounds are unique rather than members of a series of related compounds illustrating fundamental chemical trends.
The bioutility of bismuth compounds has a 250-year history that includes numerous medicinal applications; however, the mechanisms of bioactivity are not understood. Moreover, as for most compounds of bismuth, the chemical characterization of biorelevant complexes remains incomplete. Although the “heavy metal” designation has impeded application of bismuth chemistry in medicine, two compounds have been extensively used for gastrointestinal medication for decades. Pepto-Bismol contains bismuth subsalicylate, and De-Nol contains colloidal bismuth subcitrate. The use of these compounds for the treatment of travelers’ diarrhea, non-ulcer dyspepsia, nonsteroidal anti-inflammatory drug damage, and various other digestive disorders extends from the previous use of bismuth compounds in the treatment of syphilis and tumors, in radioisotope therapies, and in the reduction of the renal toxicity of cisplatin.
It’s Elemental: Bismuth
Several species of Gram positive bacteria have the ability to withstand detrimental environmental conditions by producing endospores. Endospores are resistant to heat, chemical disinfectants, dessication, and even UV and gamma radiation.
When environmental conditions become difficult to survive in, signals are sent to the cell to begin the process of sporulation. The process produces a resistant, dormant cell that awaits better conditions to begin growing again.
Endospores can be located in different places in the cell depending on the species producing them. They are called “endospores” because they develop inside the vegetative (growing) cell.
The endospore anatomy can be seen above.
From the inside out:
Core: contains dormant DNA and ribosomes
Core wall: surrounds the core
Cortex: surrounds the core wall. Made of peptidoglycan, but has fewer cross-links than vegetative cell walls.
Spore coat: surrounds the cortex. Made of several protein layers.
Exosporium: a thin layer on the outside of the spore.
Each layer contributes to the spore’s ability to withstand adverse conditions. The mechanisms by which the exposporium and spore coat protect the cell are not well understood, but it is known that they are impermeable to toxic chemicals. The core plays a role in maintaining low water content inside the spore and keeping the pH low. The most important factor protecting the DNA inside the core are called small, acid-soluble DNA-binding proteins (SASPs). These saturate the DNA and are key in providing resistance to heat, UV radiation, dessication, and chemicals.
Endospores are tricky little things! They’re really amazing testaments to what bacteria can do — but the latest mishaps at the CDC are a good reminder that spore-formers should be handled with care.
The mustached and long-tusked walrus is most often found near the Arctic Circle, lying on the ice with hundreds of companions. These marine mammals are extremely sociable, prone to loudly bellowing and snorting at one another, but are aggressive during mating season. With wrinkled brown and pink hides, walruses are distinguished by their long white tusks, grizzly whiskers, flat flipper, and bodies full of blubber.
Walruses use their iconic long tusks for a variety of reasons, each of which makes their lives in the Arctic a bit easier. They use them to haul their enormous bodies out of frigid waters, thus their “tooth-walking” label, and to break breathing holes into ice from below. Their tusks, which are found on both males and females, can extend to about three feet (one meter), and are, in fact, large canine teeth, which grow throughout their lives. Male walruses, or bulls, also employ their tusks aggressively to maintain territory and, during mating season, to protect their harems of females, or cows.
The walrus’ other characteristic features are equally useful. As their favorite meals, particularly shellfish, are found near the dark ocean floor, walruses use their extremely sensitive whiskers, called mustacial vibrissae, as detection devices. Their blubbery bodies allow them to live comfortably in the Arctic region—walruses are capable of slowing their heartbeats in order to withstand the polar temperatures of the surrounding waters.
The two subspecies of walrus are divided geographically. Atlantic walruses inhabit coastal areas from northeastern Canada to Greenland, while Pacific walruses inhabit the northern seas off Russia and Alaska, migrating seasonally from their southern range in the Bering Sea—where they are found on the pack ice in winter—to the Chukchi Sea. Female Pacific walruses give birth to calves during the spring migration north.
Only Native Americans are currently allowed to hunt walruses, as the species’ survival was threatened by past overhunting. Their tusks, oil, skin, and meat were so sought after in the 18th and 19th centuries that the walrus was hunted to extinction in the Gulf of St. Lawrence and around Sable Island, off the coast of Nova Scotia.
text and second photo source: NatGeo
First photo source
Sublime Microglia: Expanding Roles for the Guardians of the CNS
Recent findings challenge the concept that microglia solely function in disease states in the central nervous system (CNS). Rather than simply reacting to CNS injury, infection, or pathology, emerging lines of evidence indicate that microglia sculpt the structure of the CNS, refine neuronal circuitry and network connectivity, and contribute to plasticity. These physiological functions of microglia in the normal CNS begin during development and persist into maturity. Here, we develop a conceptual framework for functions of microglia beyond neuroinflammation and discuss the rich repertoire of signaling and communication motifs in microglia that are critical both in pathology and for the normal physiology of the CNS.
Though we may not often consider it, our bodies are full of fluid dynamics. Blood flow is a prime example, and, in this video, researchers describe their simulations of flow through the left side of the heart. Beginning with 3D medical imaging of a patient’s heart, they construct a computational domain - a meshed virtual heart that imitates the shape and movements of the real heart. Then, after solving the governing equations with an additional model for turbulence, the researchers can observe flow inside a beating heart. Each cycle consists of two phases. In the first, oxygenated blood fills the ventricle from the atrium. This injection of fresh blood generates a vortex ring. Near the end of this phase, the blood mixes strongly and appears to be mildly turbulent. In the second phase, the ventricle contracts, ejecting the blood out into the body and drawing freshly oxygenated blood into the atrium. (Video credit: C. Chnafa et al.)
The Development of Social Behavior in Three South American Canids
Here’s a neat paper from 1983.
The bush dog, crab-eating fox, and maned wolf are three species of canids from South America. The maned wolf is mostly solitary, with contact between males and females restricted to the breeding season and pup-rearing. Crab-eating foxes, by contrast, pair up and maintain territories together. Pups also sometimes remain with their parents past reproductive age, depending on territory availability.
Of all three species, the bush dog is the most social, living in packs much like the gray wolf or African wild dog does. This enables them to work together and kill prey much larger than themselves, like capybara.
At the time, these three species were all placed within the South American branch of Canidae, distinct from the true foxes and the true dogs. (This has since been challenged.*) The paper’s author, Maxeen Biben, chose to compare them because they had such a range of different social lifestyles.
Since the bush dog was the most social of the three, she expected it to show the most complex social development; likewise, she thought the maned wolf would have the least, and the crab-eating fox would be somewhere in between. However, some of her results were rather surprising.
This paper is extremely detailed, so I’ll try to sum up the gist of the results. I highly recommend you read through it yourself, though.
- Crab-eating foxes developed specific social behaviors about a week before the other two species.
- Bush dog puppies played together more often, cooperated in object play more often, and rested together for longer than the other two species.
- They also did not defend food items, while the other two species did.
- However, crab-eating foxes and maned wolves showed more complex social interactions and some social behaviors that the bush dogs did not (such as play-bows and grappling).
- Bush dog pups also bit one another and vocalized more frequently than the other two, making their interactions appear very aggressive. However, this aggression was brief and did not affect relationships in the long term.**
- There were no discernible sex differences in social development.
- There was no evidence of a specific dominance hierarchy forming in any of the groups of pups. All pups behaved submissively towards their parents.
Taken together, the results allowed Biben to reach some extremely interesting conclusions.
Given that maned wolves are much larger than crab-eating foxes, it is not surprising that their development lagged behind (larger size = slower growing). But considering the fact that bush dogs are about the same size as crab-eating foxes, it is surprising that their social development was slower.
Biben suggests that this is because the bush dogs are more neotonized than either of the other two species. The extension of a growth and play period is very common in the evolution of highly social species. Bush dogs even have a more paedomorphic appearance, with their rounded heads and short, stocky bodies.
The lack of more complex social behavior in bush dogs was also unexpected, but Biben theorizes that this is because bush dogs experience less conflict with members of their own species than the more solitary and territorial species do. They may need fewer signals to avoid fighting.
Biben also points out that bush dog pups had a higher incidence of submissive behavior (rolling over) which is important in maintaining a lack of aggression in large social groups.***
Finally, the lack of a discernible social hierarchy between pups of any species led Biben to criticize some earlier studies suggesting that canids such as foxes, wolves, and coyotes form dominance hierarchies as pups. She suggests that the reason these studies came up with these results is that they were carried out on captive animals that were removed from their parents or each other for long periods of time, disrupting their normal social development.
While all the litters in this study were also in captivity, they were kept together with both parents. Biben concludes that the normative social structure of canids is simply that pups are submissive to their parents and that they develop no consistent hierarchy within their litter.
Biben, M. (1983). Comparative ontogeny of social behaviour in three South American canids, the maned wolf, crab-eating fox and bush dog: implications for sociality. Animal Behaviour, 31(3), 814-826.
Image credit: Tambako the Jaguar
*In some more recent phylogenies, the bush dog is placed with tribe Canini near the African wild dog. (x)
**Other authors have suggested that the bush dog’s high frequency of vocalization and apparent aggression stems from the fact that they have less mobile faces and bodies to communicate with than other canine species. Bush dog vocalizations are quite complex. (x, x)
***Some other highly social canid species, like African wild dogs, have been observed to ‘gang up’ on a single individual within the group. Biben suggests that this may be a form of submission to the group by the individual that rolls over, but it could also be a form of group hunting play where one member inadvertently becomes the ‘victim.’ (x)
MicroRNAs (miRNAs) are small noncoding RNA molecules with big implications in cancer. The abnormal expression of specific miRNAs has been linked to development of many cancer types. Dysregulated miRNAs play a significant role in proliferation, invasion, differentiation, apoptosis, and resistance of various cancer cells, and considered as oncogenes or tumor-suppressor genes. Findings have shown abnormal expression of specific miRNAs in breast tumors is a strong indication about the resistance to conventional cancer therapy methods. Acquired cancer resistance is a complex, multifactorial occurrence that requires various mechanisms and processes, however, recent studies have suggested that resistance may be linked to treatment-induced dysregulation of miRNAs. This dysregulation of miRNAs can affect the protein expression in cells, the ability for anti-cancer drugs to reach their targets within cells, and the apoptotic pathways. Controlling the expression of these miRNAs alters the resistant phenotype of breast cancer to a nonresistant one. This review focuses on the role of dysregulated miRNAs in breast cancer that are linked to resistance against chemo-, radiation, hormone, and targeted therapies. Finally, the role of miRNAs in breast cancer metastasis is briefly discussed. For further resources related to this article, please visit the WIREs website. Conflict of interest: The authors have declared no conflicts of interest for this article.
— Wiley Interdisciplinary Reviews: RNA