Corpus Callosum : The Brain Bridge

List of images in Gray's Anatomy: IX. Neurology

Image via Wikipedia

In the two preceding posts, I’ve mentioned how marsupials, monotremes, and reptiles lack a corpus callosum, so I’d like to take the time to explain what this structure is. The corpus callosum, or colossal commissure, is a part of the brain that connects the right and left cerebral hemispheres and allows for communication between the two. It is the largest white matter structure in the brain. It also happens to be absent in fish, birds, and amphibians. Some groups have a different form of cerebral connection, like marsupials with their anterior commissure. The corpus callosum aids in functions such as brachiation (swinging through tree limbs using their arms) in arboreal primates by allowing coordination of the limbs.

Agenesis of the corpus callosum is a rare congenital disorder in which the corpus callosum is partially or completely absent. Common symptoms include:

  • vision impairments
  • low muscle tone (hypotonia)
  • poor motor coordination
  • delays in motor milestones such as sitting and walking
  • low perception of pain
  • delayed toilet training
  • chewing and swallowing difficulties
  • cognitive disabilities
  • social difficulties (possibly due to impaired facial processing)
There is currently no treatment, but therapy may be beneficial. The corpus callosum is not capable of regeneration.

If you’d like to see a pretty neat episode of House MD that involves “split brain“, check out Season 5 Episode 24, Both Sides Now.

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Sources

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Milo’s Megacolon


X-ray of megacolon via askavetquestion.com

A cat named Milo was admitted into the hospital on Tuesday to investigate constipation and his lack of appetite for the previous 5 days. It turns out poor Milo has megacolon. “Megacolon is a term used to describe a very dilated, flabby, incompetent colon.  This usually occurs secondary to chronic constipation and retention of feces, but may be a congenital dysfunction.”(#1) The size of the colon will then make it more difficult to pass stool as it will be of larger diameter than its intended point of exit.

At this point, enemas, laxatives and other traditional methods of constipation relief would have done little for Milo. Surgery is the only real avenue for improving his quality of life. Unfortunately, the surgery requires a specialist and runs about $2000. The owners don’t have the necessary funds and Milo was scheduled for euthanasia Wednesday. For whatever reason, he was rescheduled for Thursday (I wasn’t at the hospital) and had been given an enema on Wednesday for a minor amount of relief. In terms of appetite, he was quite a fan of the a/d offered to him. One of the vet techs showed me his x-ray and it looks very similar to the one in the image above.

He was a very sweet cat while hanging out with us in treatment so I’m pretty sad that there’s nothing that we can really do for him. I just hope he makes some nice friends in kitty heaven.

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Sources

  1. ACVS – Feline Megacolon

Myotonia Congenita. The Disorder Behind the Fainting Goat.

If you haven’t seen these goats, here you go:

They suffer from a genetic disorder called myotonia congenita. It is a congenital disease (present at birth) that essentially causes their muscles to freeze for 10 seconds when they are startled. Younger goats are more prone to actually falling, while older goats learn to spread their legs so they still sort of walk stiffly. The disorder affects gene CLCN1 via a mutation. The CLCN1 protein controls normal function of skeletal muscle cells.

Sources:

  1. Wikipedia – Fainting Goat
  2. Wikipedia – Myotonia congenita

VMCAS Deadline Countdown: 12 days

The Stages of Toxoplasma gondii

T. gondii constructing daughter scaffolds with...

Image via Wikipedia

As stated in Toxoplasma gondii, today I’m going to break down the stages of the parasite. Those stages are:

  • Sporulated oocysts (sporozoites) from environment
  • Tissue cysts containing bradyzoites in raw/undercooked meat
  • Tachyzoites in tissues
  • Entero-epithelial stages (only in cats)

Oocysts are produced non-sporulated but will sporulate in about 2 days. They are about 10×10 µm and millions can be produced within days. Cats can develop strong immunity to this stage.

In the intermediate host, the life cycle is as follows:

  • Excystation of sporozoites
  • Sporozoites –> Tachyzoites
  • Tachyzoites disseminate infection and eventually become bradyzoites or tissue cysts
  • Latent infection
  • Endodyogeny (a form of sexual reproduction)

Tachyzoites have a fondness for neural and cardiac tissue but can infect any nucleated cell in the body. This is the stage that crosses into the placenta and causes congenital infections. Rapid division of tachyzoites is what causes tissue destruction, the spread of infection and lesions.

Bradyzoites (“brady” = slow) are responsible for tissue cysts. They can be present in any organ and survive for the life of the infected animal since they are resistant to the drugs used to treat Toxoplasmosis. If the host is immunocompromised, infection can be reactivated and intermediate hosts can infect one another. Bradyzoites are at fault for initiating meat induced infection, on top of being the only stage to give rise to entero-epithelial stages.

Once again, the etero-epithelial stages are only found in cats. There are 5 types of entero-epithelial schizonts (which will not be listed). This is where the sexual stages/oocysts are produced.

Overall, Toxoplasma gondii was the most successful parasite discussed in my Intro Parasitology course.

:: Information from this post is from my notes from an Introductory Parasitology class taught by Dr. Zajac at Virginia Tech ::

Polydactyly

Polydactyl Cat

Image by failing_angel via Flickr

The inspiration for this post is from a cat I met while shadowing at a Veterinary Hospital. I believe she was a Maine Coon and the poor thing came in with an extra digit on each of her front paws. The bad part wasn’t the digits, but the ingrown nails between them. Oddly enough, the nails had no pad associated with them so they were just growing from the webbing. The right paw was the worst with the actual ingrown nail (and a possible infection) and the left paw’s randomly sprouted nail had grown to spiral like a ram horn. However, the nails are beside the point. I’ve always been intrigued by diseases, especially ones that can result in something sprouting an extra limb, so I figure why not dive into the matter of polydactyly, also known as supernumerary digits.

As you might have guessed, polydactyly is a condition where an animal has extra fingers or toes. The extra digit may be fleshy, contain bones, or even be fully functioning. The postaxial manifestation (on the side of the little finger) is most common, followed by preaxial (by the thumb) and then central (the middle three fingers). The new digit may jut from an existing, normal digit, or (when associated with the hand) from the wrist as do the other digits. The condition is a congenital anomaly, meaning it exists at or before birth.

The U.S. National Library of Medicine (NLM)/National Institutes of Health (NIH) list the following causes for polydactyly:


While supernumerary digits  may be associated with one of the preceding syndromes, or perhaps some even unlisted, it can also occur on its own. According to NIH, African-Americans, such as myself, are more prone to inheriting a 6th digit than other ethnic groups, which in most cases is not associated with a genetic disease. When occurring by itself, polydactyly might be due to an autosomal dominant mutation in a single gene.

Here’s a very short video. Very briefly, you can see the supernumerary digit.