Snapshot: What is Neurogenesis?

Neurons are the cells that serve as building blocks of the nervous system. The brain contains an enormous variety of neurons, and they all need to get a start somewhere. The process by which neurons are formed is called neurogenesis.

An artist’s drawing of neurons in the brain. Photo used under license by Andrii Vodolazhskyi/Shutterstock.com.

When does neurogenesis happen?

Nearly all neurogenesis occurs before the age of 2 when the brain is in the early stages of being formed and refined. While most cells in the body are replaced as they wear out or get injured, neurons in the brain do not. By young adulthood, the brain has largely stopped making new neurons. Other than serving as an excellent reason to wear a helmet and otherwise protect your head from injury, this lack of new neuron formation doesn’t have a noticeable effect on how we go about our daily lives. After all, neurons are an incredibly adaptable cell type that readily change in response to a person’s environment and experiences.

In the past few decades, we have learned that there is an exception to the “all neurons are born early in life” rule. Some research has shown that new neurons can, in fact, be formed during adulthood in specific brain areas. For example, the hippocampus, a brain structure important for its role in forming and maintaining memories, continues to create neurons over the course of one’s life.

The purpose of these newly generated neurons is still debated. However, numerous studies have shown that neuron formation in the hippocampus is reduced in instances of psychiatric and neurodegenerative disorders. This includes certain types of ataxia like SCA1. This is thought to contribute to changes in cognitive function and mood, though the exact mechanisms are still being determined.

Why is neurogenesis interesting for the spinocerebellar ataxias (SCAs), aren’t these neurodegenerative disorders?

Since the discovery of neurodegenerative disorders, most research has focused on symptoms and how to delay symptom onset. This view sees neurodegenerative disorders, like the SCAs, as outcomes of mid to late-life when the toxic effects of mutant proteins become suddenly rampant. However, these disorders are caused by proteins that are present from the very earliest stages of brain formation.

In 2018, researchers studying SCA1 found that neurogenesis is increased in the cerebellum of young mice. This changed how the cerebellum communicates with the rest of the brain. This suggests that cerebellar function can be affected by more than neuronal loss. It could be of wider interest in the SCAs given the cerebellar dysfunction that is common between them. No research on cerebellar neurogenesis has been performed in other SCAs by this point. However, there are some indications that neurogenesis may also be altered in SCA2.

Additionally, Huntington’s Disease, a polyglutamine repeat disorder in the same disease family as several SCAs, has been shown to have increased neurogenesis in the cortex in both young mice and prenatal babies. The combination of these recent studies has made early neuron formation an area of key interest in the study of neurodegenerative disorders.

Current theories in the field contend that while the brain can compensate for changes in neuron numbers in early life, altered neurogenesis could be creating unique brain circuitry in individuals with known disorder-causing protein mutations. These changes could make them more vulnerable to neuronal dysfunction and neurodegeneration later in life.

Evidence for changed neurogenesis in SCAs, both early and late in life, adds a new layer of consideration to what we broadly think of as a mid- to late-life neurodegenerative disease. Additional research in coming years will hopefully provide more insight into how these additional facets of neural health may inform the development of new therapies.

If you would like to learn more about neurogenesis, take a look at these resources by the Queensland Brain Insitute and News-Medical.

Snapshot written by Carrie Sheeler and edited by Dr. Chloe Soutar.

Additional References

Cvetanovic M, Hu YS, Opal P. Mutant Ataxin-1 Inhibits Neural Progenitor Cell Proliferation in SCA1. Cerebellum. 2017 Apr;16(2):340-347. doi: 10.1007/s12311-016-0794-9. PMID: 27306906; PMCID: PMC5510931.

Shukla JP, Deshpande G, Shashidhara LS. Ataxin 2-binding protein 1 is a context-specific positive regulator of Notch signaling during neurogenesis in Drosophila melanogaster. Development. 2017 Mar 1;144(5):905-915. doi: 10.1242/dev.140657. Epub 2017 Feb 7. PMID: 28174239; PMCID: PMC5374347.

Xia G, Santostefano K, Hamazaki T, Liu J, Subramony SH, Terada N, Ashizawa T. Generation of human-induced pluripotent stem cells to model spinocerebellar ataxia type 2 in vitro. J Mol Neurosci. 2013 Oct;51(2):237-48. doi: 10.1007/s12031-012-9930-2. Epub 2012 Dec 9. PMID: 23224816; PMCID: PMC3608734.

Barnat M, Capizzi M, Aparicio E, Boluda S, Wennagel D, Kacher R, Kassem R, Lenoir S, Agasse F, Braz BY, Liu JP, Ighil J, Tessier A, Zeitlin SO, Duyckaerts C, Dommergues M, Durr A, Humbert S. Huntington’s disease alters human neurodevelopment. Science. 2020 Aug 14;369(6505):787-793. doi: 10.1126/science.aax3338. Epub 2020 Jul 16. PMID: 32675289; PMCID: PMC7859879.

Snapshot: What is Gait Analysis in Ataxia Mouse Models?

A key role of the cerebellum is to control and fine-tune coordinated movement such as walking. Although walking is an unconscious behaviour, it is actually very complex and requires many systems to work together. The specific mannerisms and patterns of coordinated movement that make up how an individual walks are called gait.

Since ataxia affects cells in the cerebellum, many ataxia patients exhibit a change in their gait. This change can reduce their mobility and be disruptive to daily life. Analyzing gait using behavioural experiments in ataxia mouse models helps researchers to better understand the disease. But how exactly does one study gait patterns in a mouse?

Black rat walking in front of white background
Photo used under license by Eric Isselee/Shutterstock.com.

Traditionally, a researcher measures gait by performing a footprint analysis that uses non-toxic water-coloured paint and a long strip of white paper. The front and back feet of the mouse are dipped into two different colours of paint. Then the mouse then runs across the paper leaving a trail of coloured footprints to be analyzed. This allows for several gait measurements to be taken. From this, the researcher can then determine how ataxia changed the mouse’s gait. For example, a researcher can look at if the mouse takes shorter strides than a healthy control or whether the mouse tends to walk in a more crooked manner.

Although easy to perform, footprint analysis is time-consuming and highly prone to error as the experimenter does all measurements with a ruler by hand after the mouse has run. Since gait is a complex action with many variables, some subtle differences may be difficult to detect this way. Luckily, researchers have developed several digital gait analysis systems, such as the DigiGait, CatWalk, and TreadScan systems. These digital gait devices make use of transparent corridors with cameras underneath that allow the researcher to record the running behaviour of the animal. Researchers then use software to automatically detect and analyze the footprints.

One lab has taken gait analysis even further. They developed a method to detect extremely subtle differences in gait that the human eye cannot detect. This technique, called LocoMouse, was developed by the Carey lab to analyze patterns of limb movements, rather than simply footprints. LocoMouse utilizes artificial intelligence to recognize and analyze the movement of limb, tail, and head position in a walking mouse.

Using this, the Carey lab has shown a significant difference between a healthy mouse and one with ataxia. Most importantly, the method also detects differences between different ataxia mouse models. By uncovering subtle differences in gait, researchers may better understand the different underlying physiological changes in the cerebellum in different ataxias.

It should be noted that a key pitfall of studying gait in mice is that they are four-legged while humans walk on two legs. This is important, and means that the variables that affect gait in a mouse will be different than those of a human. There may not be a direct correlation between gait changes in ataxia patients and gait changes in mice. That being said, gait analysis remains an important tool in the ataxia researchers’ toolbox. It will continue to provide critical insight into how ataxic physiology affects behaviour.

If you would like to learn more about gait analysis in mice, take a look at these resources by the Noldus Information Technology and Mouse Specifics Inc.

Snapshot written by Eviatar Fields and edited by Dr. Chandana Kondapalli.

Snapshot: What is the Morris Water Maze Test?

Spinocerebellar ataxias (SCAs) are well known for worsening motor coordination symptoms caused by the degeneration of the cerebellum. Yet, increasing reports indicate that broader changes are occurring in the brains of some SCA patients. This includes changes in the hippocampus, a brain region critical for learning and memory. One way to test learning and memory in mice is the Morris Water Maze Test. Researchers use this test on SCA mouse models to investigate how and when learning and memory symptoms arise. More importantly, we can also use this test to evaluate the effect of potential treatments on learning and memory.

white mouse swimming with its head poking up above the water
Although mice can swim quite well, they don’t like swimming. The Morris Water Maze takes advantage of this to test the learning and memory of mice. Photo used under license by Aleksandar Risteski/Shutterstock.com.

The Morris Water Maze consists of a large circular pool of opaque water. A platform is placed in the pool just under the surface of the water so that the mouse won’t be able to see it. Though mice are good swimmers, they don’t particularly enjoy swimming. Mice will always attempt to find the platform as quickly as possible. Shapes on the walls around the pool help the mice orient themselves within the pool (first panel in the figure below).

The first time a mouse swims in the pool (second panel in the figure), the mouse tends to swim aimlessly around until they eventually find the hidden platform. Each subsequent time the mouse swims in the pool, the mouse will get better and better. Using the shapes on the wall to help identify where they are in the pool, the mouse will eventually learn and memorize the platform’s location.

First day, mouse does not know wehere the plaform is an swims a lot. Second day, the mouse still swims a while but remembers where the platform is. On the last day, the mouse knows where the platform is and goes right there.
The three steps in the Morris Water Maze. Image made by Larissa Nitschke use BioRender.

As that happens, they will be better and better at the task. Eventually, the mice will swim immediately to the platform when placed in the pool (third panel in the figure). Researchers can measure this improvement by measuring how much time it takes the mouse to reach the platform and the length of its path to the platform. Additionally, to assess the strength of the memory, researchers can take out the platform from the pool in what is called a “probe trial”. Mice that spend more time in the area where the platform used to be are considered to have built the strongest memories of that location.

As is the case for some SCA mouse models, mice with impaired learning and memory have more difficulty learning and remembering the correct location of the platform. As a result, they spend a longer time searching for and swim longer distances to the platform. Overall, they display a poorer improvement over time. By using the Morris Water Maze Test on SCA models that receive different treatments, scientists can then further test which therapy could improve their learning and memory symptoms. Therefore, the Morris Water Maze Test may help identify new therapeutic strategies to treat learning and memory problems in patients.

If you would like to learn more about the Morris Water Maze, take a look at these resources by the Scholarpedia and JOVE.

Snapshot written by Carrie Sheeler and edited by Dr. Larissa Nitschke.

Snapshot: What is the balance beam test?

When you think of a balance beam, you might think of gymnastics. For humans, a balance beam is a surface where we perform jumps, flips, and other athletic feats. Whether it’s a child taking their first class, or an Olympic athlete going for gold, the balance beam requires both balance and coordination. When a scientist puts a mouse through the balance beam test, they don’t ask them to do this kind of complicated routine, but they are testing those same abilities.

Little Black Mouse on a White Background
Little Black Mouse on a White Background. Photo used under license by Michiel de Wit/Shutterstock.com.

The equipment setup for the balance beam test is simple: two platforms with a beam running between them plus lots of padding underneath so the mouse doesn’t get hurt if it falls off. Over multiple days, the scientist will train the mouse to run across the beam from one platform to another. Once the mouse has been trained, it will go through multiple official test runs. In these tests, the scientist will measure the time it takes for the mouse to cross the beam. They will also count the number of times one of its paws slips off the beam during the crossing. You can see some videos of mice doing the test here.

Mice that have problems with balance and coordination usually take longer to cross the balance beam and have more paw slips during the crossing. The mice might take longer to cross because they are clinging to the beam to try to stay on. Their paws might slip more because they cannot coordinate their movements properly. The scientist can also compare the measurements from the first day of training with the measures taken during the official runs. This shows how well the mouse learned to stay on the beam. This is useful because learning how to do a task and performing the task are two different things. Some parts of the brain are more important for learning, while others are more important for doing the task. Thus, telling those two aspects apart can be useful.

Mouse cossing a balance beam connecting two platforms

A typical balance beam setup, with two platforms and a beam between them. Image by Amy Smith-Dijak.

The balance beam test has been used to understand balance and coordination in both healthy mice and mouse models of disease. In healthy mice, scientists studying the basic biology of balance and coordination use this assay to test if changing the way particular parts of the brain work changes the mouse’s performance. For diseases in which lack of balance and coordination are major features, such as spinocerebellar ataxias, this test is a simple way to check how fast the disease progresses in mouse models. The assay can further be used to test possible treatments for these diseases: better scores after the treatment indicate that the therapy helped the mice improve their balance and coordination.

To sum it up, the balance beam test is a simple and effective assay to measure a mouse’s balance and coordination. Its use helps scientists to understand the basic biology of balance and coordination, as well as uncover why they are impaired in some diseases. Using the balance beam test on mouse models of disease that underwent different treatments, scientists can further measure if the therapy would improve the mouse’s balance and coordination. Therefore, the balance beam test might even help to find new treatments for motor coordination diseases.

If you would like to learn more about the balance beam test, take a look at these resources by the Maze Engineers and Creative Biolabs.

Snapshot written by Dr. Amy Smith-Dijak and edited by Dr.Larissa Nitschke.

2 Minuti di Scienza: Come si misura clinicamente la gravità dei sintomi in pazienti atassici

Il coordinare facilmente ed efficacemente movimenti  come il parlare e il camminare è essenziale nello svolgimento della vita quotidiana. L’abilità di orchestrare questi movimenti con successo è generalmente chiamata “coordinazione mootoria”. Anche se i pazienti di SCA in genere sono in grado di iniziare movimenti coorporei, la loro abilitá di eseguirli in modo agevole e preciso è alterata. Per esempio, è possibile notare l’incordinazione motoria in pazienti atassici che non riescono a camminare lungo una linea retta, o nella difficoltà che hanno nel deglutire. Questi ed altri problemi motori possono notevolmente inficiare la vita quotidiana. Poter valutare fino a che punto un paziente sia in grado di fare questi movimenti offre un’ indicazione della gravità della patologia in ciascun individuo affetto dalla malattia.

Black pencil lying on top of paper that has scoring chart on it
Immagine ottenuta da Pixabay, Pexels.com

A differenza di ciò che analisi cliniche di routine misurano, come la pressione sanguigna o i livelli di zucchero nel sangue, non esiste una semplice misura per quantificare i movimenti umani. Per sopperire a questa carenza, sono state sviluppate numerose unità di misura con l’intento di assegnare una quantificazione standard as esami di coordinazione motoria.  Una di queste misure è la Scala per la Valutazione e la Classificazione dell’Atassia (SVCA). Un medico esperto (generalmente un neurologo) analizza la capacità del paziente di portare a termine alcuni comandi ( come ad esempio alzarsi in piedi o camminare) e poi, usando la SVCA, assegna  un voto per ogni comando. La procedura dura  circa 15-20 minuti, e in genere include i seguenti esami:

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