Stabilizing the Blood-Brain Barrier Against Invading Parasites

African trypanosomes, a brain-infecting parasite, surrounded by red blood cells. Image Credit: Centers for Disease Control and Prevention

When it comes to defending the brain from parasites, the immune system, if not kept under tight control, can actually do more harm than good. The brain is immunologically privileged: it is protected from outside threats by both the blood-brain barrier, a tightly-packed layer of cells that allows only certain molecules to enter the brain from the bloodstream, and by specialized immune cells located inside the barrier. When the brain comes under siege by parasites, immune cells from the bloodstream are recruited to the area to help attack the invaders. This flooding of immune cells into the tissue surrounding the brain damages the cells in the blood-brain barrier, inadvertently allowing more parasites into the brain. Olivera et al. show that nitric oxide helps prevent immune cells from overwhelming the blood-brain barrier. When immune cells first reach the brain from the bloodstream, they stimulate immune cells in the brain to produce nitric oxide. As more nitric oxide is produced, it inhibits signaling molecules that would normally recruit additional immune cells to the brain. This negative-feedback loop ensures that some immune cells arrive to provide additional defenses for the brain, but not so many that damage is caused to the fortification keeping the parasites at bay.

- Stephanie DeMarco
Staff Writer, Signal to Noise Magazine
PhD Candidate, Molecular Biology

 

Learning what makes us happy, with a little help from dopamine

Photo credit: Allan Ajifo (aboutmodafinil.com), Wikimedia Common

Photo credit: Allan Ajifo (aboutmodafinil.com), Wikimedia Common

Imagine you are eating a delicious slice of chocolate cake. You may feel happy inside just thinking about it - you don’t even need to see, smell, or taste the cake. How does your brain create this effect? There are neurons in your brain which produce a neurotransmitter (a chemical messenger that neurons use to communicate with each other) called dopamine. High levels of dopamine make us feel good. When you think of the cake, neurons in your brain release dopamine, which relays a message to other neurons to tell your body to feel happy. This is called a reward response: it helps us to learn and remember things in our environment that we like [1]. To better understand how dopamine-producing neurons regulate the reward response, researchers can look to the fruit fly as a model system. In the latest issue of Current Biology, Rohwedder et al. identified a novel set of dopamine-producing neurons in the larval brain which appear to connect with neurons of the mushroom body, a known center for learning and memory in the fly [2]. By expressing genes in these neurons that either killed them or caused them to become active, they showed that depending on where these dopamine-producing neurons contact the mushroom body, this results in a reward response to a different type of sugar. This novel set of neurons behaves in stark contrast to a previously described set of dopamine-producing neurons, which are known to be important for aversive behaviors (for instance, when you spit something out because it tastes awful). Identification of distinct sets of neurons that regulate reward versus aversion is a common feature observed in adult fruit flies and in mammals, but until now has never been observed in developing individual neurons. This study lays the groundwork for the possibility of studying in great detail the reward-aversion behavioral paradigm at the level of single neurons.

Jennifer Lovick (@drjkyl)
Senior Editor, Science in Entertainment, Signal to Noise
PhD, Molecular, Cell, and Developmental Biology

 

Reference:
1. “Dopamine Is __________ Is it love? Gambling? Reward? Addiction?” Bethany Brookshire for Slate. July 3 2013. www.slate.com/articles/health_and_science/science/2013/07/what_is_dopamine_love_lust_sex_addiction_gambling_motivation_reward.html

2. Rohwedder A, Wenz NL, Stehle B, Huser A, Yamagata N, Zlatic M, Truman JW, Tanimoto H, Saumweber T, Gerber B, Thum AS. Four individually identified paired dopamine neurons signal reward in larval Drosophila. Curr Biol. 26, 661-669 (2016). DOI: dx.doi.org/10.1016/j.cub.2016.01.012

Studying Neural Circuits Using Fluorescence Confocal Microscopy

Studying Neural Circuits Using Fluorescence Confocal Microscopy

Microscopes magnify very small objects that are difficult to see with the naked eye using lenses and a source of illumination. Confocal microscopes use a combination of lenses and mirrors illuminated by lasers to view small samples that are labeled with fluorescent molecules (called fluorescence confocal microscopy). 

Read More

Neurons Tell Time

Female fruit fly, Drosophila melanogaster (This work has been released into the public domain by its author, Botaurus at German Wikipedia.)

Our ability to see when it’s light or dark outside helps us tell time and also helps our bodies pattern our daily routines, such as when we eat or sleep – but how do cells in our brain, which are important for creating these patterns, know? The circadian or molecular clock consists of molecules which activate and synchronize neurons that regulate organisms’ behaviors in accordance with the 24-hour light/dark cycle. Liang et al. developed a technique to study the activity of these neurons (by measuring calcium levels within the cells) in brains of live fruit flies. They observed that some neurons are active in the morning while others are active in the evening, corresponding with morning or evening locomotor activities such as flying or walking, and that this activity is regulated by the molecular clock in conjunction with the neuropeptide pigment-dispersing factor (PDF). This system, then, acts as a timing mechanism telling neurons when to become active so that they can initiate behaviors at the right time of day.

Jennifer Lovick (@drjkyl)
Senior Editor, Science in Entertainment, Signal to Noise Magazine
PhD, Molecular, Cell, and Developmental Biology
 

References:

Liang, X., Holy, T. E. & Taghert, P. H. Synchronous Drosophila circadian pacemakers display nonsynchronous Ca2+ rhythms in vivo. Science. 351, 976-981 (2016). DOI: 10.1126/science.aad3997