The FIRSTS: the von Economo neurons (1881, 1904, 1926)

A von Economo neuron, also known as a spindle neuron, is a unique cell with several interesting characteristics:

1) It has a long axon and on the opposite side of the cell body has only one long dendrite, resembling a spindle and hence the nickname.

2) It is to be found only in humans, apes, elephants, dolphins, whales, and a few other animals known for their intricate social structure.

3) In humans, they exist only in the frontal part of the brain.

4) It is thought to be important for social awareness.

In all fairness, these cells should be called Betz cells, or at least Ramón y Cajal cells because these neuroanatomists mentioned their existence in 1881 and 1904, respectively. But Betz already has his own neurons, and Ramón y Cajal, well… his fame is established already. But von Economo “made a more complete description of their morphology and mapped their specific locations in human cortex” (Allman et al., 2011)

So what do we know about von Economo? Quite a lot, thanks to Triarhou, an excellent biographer. Constantin von Economo (1876–1931) was born in Brăila, Romania to a wealthy family of Greek descent. Shorty after his birth, the family moved from Romania to Austria where the father acquired a “von” in front of his name by way of elevation to the rank of baron.

Von Economo went to medical school  in Vienna, traveled a lot across the globe, graduated, spent some more time here and there learning psychiatry, physiology, neurology and such with some Big Names, then returned to Vienna where he followed the classic academic path (for his time). He was a prolific writer, having published at least 139 scientific works in a relatively short time.

Besides the spindle neurons, he is also known for publishing an awesome brain atlas in 1925 (with Georg Koskinas) and for investigating in detail a mysterious and weird disease, encephalitis lethargica (the ‘von Economo disease’). This disease has unknown causes to the day, partly because it is very difficult to study, having virtually disappeared form the face of the Earth after a furious epidemic in 1926.  But about that enigma some other time.

For now, enjoy von Economo’s drawings.

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Composite image of the four drawings by von Economo (1926) in doi:10.1007/BF02970950.

Notes: 1) One last thing. Although according to Springer’s website the copyright for the von Economo paper I’m citing should have expired, Springer still charges a lot of money to obtain it (if you don’t have an institutional license like some of us, the fortunates, that is). I have attempted to contact Springer about it with no luck. Anyway, if you want it, email me at scientiaportal@gmail.com. It’s been more than 70 years since the death of the author, so it should be public domain.

2) I have no idea why people reference the Ramón y Cajal’s Textura del Sistema Nervioso del Hombre y de los Vertebrados as published in 1889. I got it from Google Books and it says 1904 on it.

References:

  1. von Economo, C. (1926). Eine neue Art Spezialzellen des Lobus cinguli und Lobus insulae (‘A new kind of special cells in the cingulum and insula’). Zeitschr. Ges. Neurol Psychiatr (Berlin), 100: 706–712. DOI: 10.1007/BF02970950. ARTICLE
  2. Allman JM, Tetreault NA, Hakeem AY, Manaye KF, Semendeferi K, Erwin JM, Park S, Goubert V, & Hof PR (Apr 2011). The von Economo neurons in the frontoinsular and anterior cingulate cortex. Annals of the New York Academy of Sciences, 1225:59-71. PMID: 21534993. PMCID: PMC3140770. DOI: 10.1111/j.1749-6632.2011.06011.x. ARTICLE | FREE FULLTEXT PDF 
  3. Triarhou, LH (14 Apr 2006, Epub 28 Feb 2006). The signalling contributions of Constantin von Economo to basic, clinical and evolutionary neuroscience. Brain Research Bulletin, 69 (3): 223–243. PMID: 16564418, DOI: 10.1016/j.brainresbull.2006.02.001. ARTICLE

By Neuronicus, 25 September 2016

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Who invented optogenetics?

Wayne State University. Ever heard of it? Probably not. How about Zhuo-Hua Pan? No? No bell ringing? Let’s try a different approach: ever heard of Stanford University? Why, yes, it’s one of the most prestigious and famous universities in the world. And now the last question: do you know who Karl Deisseroth is? If you’re not a neuroscientist, probably not. But if you are, then you would know him as the father of optogenetics.

Optogenetics is the newest tool in the biology kit that allows you to control the way a cell behaves by shining a light on it (that’s the opto part). Prior to that, the cell in question must be made to express a protein that is sensitive to light (i.e. rhodopsin) either by injecting a virus or breeding genetically modified animals that express that protein (that’s the genetics part).

If you’re watching the Nobel Prizes for Medicine, then you would also be familiar with Deisseroth’s name as he may be awarded the Nobel soon for inventing optogenetics. Only that, strictly speaking, he did not. Or, to be fair and precise at the same time, he did, but he was not the first one. Dr. Pan from Wayne State University was. And he got scooped.98.png

The story is at length imparted to us by Anna Vlasits in STAT and republished in Scientific American. In short, Dr. Pan, an obscure name in an obscure university from an ill-famed city (Detroit), does research for years in an unglamorous field of retina and blindness. He figured, quite reasonably, that restoring the proteins which sense light in the human eye (i.e. photoreceptor proteins) could restore vision in the congenitally blind. The problem is that human photoreceptor proteins are very complicated and efforts to introduce them into retinas of blind people have proven unsuccessful. But, in 2003, a paper was published showing how an algae protein that senses light, called channelrhodopsin (ChR), can be expressed into mammalian cells without loss of function.

So, in 2004, Pan got a colleague from Salus University (if Wayne State University is a medium-sized research university, then Salus is a really tiny, tiny little place) to engineer a ChR into a virus which Pan then injected in rodent retinal neurons, in vivo. After 3-4 weeks he obtained the expression of the protein and the expression was stable for at least 1 year, showing that the virus works nicely. Then his group did a bunch of electrophysiological recordings (whole cell patch-clamp and voltage clamp) to see if shining light on those neurons makes them fire. It did. Then, they wanted to see if ChR is for sure responsible for this firing and not some other proteins so they increased the intensity of the blue light that the ChR is known to sense and observed that the cell responded with increased firing. Now that they saw the ChR works in normal rodents, next they expressed the ChR by virally infecting mice who were congenitally blind and repeated their experiments. The electrophysiological experiments showed that it worked. But you see with your brain, not with your retina, so the researchers looked to see if these cells that express ChR project from the retina to the brain and they found their axons in lateral geniculate and superior colliculus, two major brain areas important for vision. Then, they recorded from these areas and the brain responded when blue light, but not yellow or other colors, was shone on the retina. The brain of congenitally blind mice without ChR does not respond regardless of the type of light shone on their retinas. But does that mean the mouse was able to see? That remains to be seen (har har) in future experiments. But the Pan group did demonstrate – without question or doubt – that they can control neurons by light.

All in all, a groundbreaking paper. So the Pan group was not off the mark when they submitted it to Nature on November 25, 2004. As Anna Vlasits reports in the Exclusive, Nature told Pan to submit to a more specialized journal, like Nature Neuroscience, which then rejected it. Pan submitted then to the Journal of Neuroscience, which also rejected it. He submitted it then to Neuron on November 29, 2005, which finally accepted it. Got published on April 6, 2006. Deisseroth’s paper was submitted to Nature Neuroscience on May 12, 2005, accepted on July, and published on August 14, 2005… His group infected rat hippocampal neurons cultured in a Petri dish with a virus carrying the ChR and then they did some electrophysiological recordings on those neurons while shining lights of different wavelengths on them, showing that these cells can be controlled by light.

There’s more on the saga with patent filings and a conference where Pan showed the ChR data in May 2005 and so on, you can read all about it in Scientific American. The magazine is just hinting to what I will say outright, loud and clear: Pan didn’t get published because of his and his institution’s lack of fame. Deisseroth did because of the opposite. That’s all. This is not about squabbles about whose work is more elegant, who presented his work as a scientific discovery or a technical report or whose title is more catchy, whose language is more boisterous or native English-speaker or luck or anything like that. It is about bias and, why not?, let’s call a spade a spade, discrimination. Nature and Journal of Neuroscience are not caught doing this for the first time. Not by a long shot. The problem is that they are still doing it, that is: discriminating against scientific work presented to them based on the name of the authors and their institutions. Personally, so I don’t get comments along the lines of the fox and the grapes, I have worked at both high profile and low profile institutions. And I have seen the difference not in the work, but in the reception.

Personally, so I don’t get comments along the lines of the fox and the grapes, I have worked at both high profile and low profile institutions. And I have seen the difference not in the work, but in the reception.

That’s my piece for today.

Source:  STAT, Scientific American.

References:

1) Bi A, Cui J, Ma YP, Olshevskaya E, Pu M, Dizhoor AM, & Pan ZH (6 April 2006). Ectopic expression of a microbial-type rhodopsin restores visual responses in mice with photoreceptor degeneration. Neuron, 50(1): 23-33. PMID: 16600853. PMCID: PMC1459045. DOI: 10.1016/j.neuron.2006.02.026. ARTICLE | FREE FULLTEXT PDF

2) Boyden ES, Zhang F, Bamberg E, Nagel G, & Deisseroth K. (Sep 2005, Epub 2005 Aug 14). Millisecond-timescale, genetically targeted optical control of neural activity. Nature Neuroscience, 8(9):1263-1268. PMID: 16116447. DOI: 10.1038/nn1525. doi:10.1038/nn1525. ARTICLE 

By Neuronicus, 11 September 2016

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THE FIRSTS: The Mirror Neurons (1988)

There are some neurons in the human brain that fire both when the person is doing some behavior and when watching that behavior performed by someone else. These cells are called mirror neurons and were first discovered in 1988 (see NOTE) by a group of researchers form the University of Parma, Italy, led by Giacomo Rizzolatti.

The discovery was done by accident. The researchers were investigating the activity of neurons in the rostral part of the inferior premotor cortex (riPM) of macaque monkeys with electrophysiological recordings. They placed a box in front of the monkey which had various objects in it. When the monkey pressed a switch, the content of the box was illuminated, then a door would open and the monkey reached for an object. Under each object was hidden a small piece of food. Several neurons were discharging when the animal was grasping the object. But the researchers noticed that some of these neurons ALSO fired when the monkey was motionless and watching the researcher grasping the objects!

The authors then did more motions to see when exactly the two neurons were firing, whether it’s related to the food or threatening gestures and so on. And then they recorded from some 182 more neurons while the monkey or the experimenter were performing hand actions with different objects. Importantly, they also did an electromyogram (EMG) and saw that when the neurons that were firing when the monkey was observing actions, the muscles did not move at all.

They found that some neurons responded to both when doing and seeing the actions, whereas some other neurons responded only when doing or only when seeing the actions. The neurons that are active when observing are called mirror neurons now. In 1996 they were identified also in humans with the help of positron emission tomography (PET).

88mirror - Copy
In yellow, the frontal region; in red, the parietal region. Credits: Brain diagram by Korbinian Brodmann under PD license; Tracing by Neuronicus under PD license; Area identification and color coding after Rizzolatti & Fabbri-Destro (2010) © Springer-Verlag 2009.

It is tragicomical that the authors first submitted their findings to the most prestigious scientific journal, Nature, believing that their discovery is worth it, and rightfully so. But, Nature rejected their paper because of its “lack of general interest” (Rizzolatti & Fabbri-Destro, 2010)! Luckily for us, the editor of Experimental Brain Research, Otto Creutzfeld, did not share the Nature‘s opinion.

Thousands of experiments followed the tremendous discovery of mirror neurons, even trying to manipulate their activity. Many researchers believe that the activity of the mirror neurons is fundamental for understanding the intentions of others, the development of theory of mind, empathy, the process of socialization, language development and even human self-awareness.

NOTE: Whenever possible, I try to report both the date of the discovery and the date of publication. Sometimes, the two dates can differ quite a bit. In this case, the discovery was done in 1988 and the publishing in 1992.

 References:

  1. di Pellegrino G, Fadiga L, Fogassi L, Gallese V, & Rizzolatti G (October 1992). Understanding motor events: a neurophysiological study. Experimental Brain Research, 91(1):176-180. DOI: 10.1007/BF00230027. ARTICLE  | Research Gate FULLTEXT PDF
  2. Rizzolatti G & Fabbri-Destro M (Epub 18 Sept 2009; January 2010). Mirror neurons: From discovery to autism. Experimental Brain Research, 200(3): 223-237. DOI: 10.1007/s00221-009-2002-3. ARTICLE  | Research Gate FULLTEXT PDF 

By Neuronicus, 15 July 2016

Autism cure by gene therapy

shank3 - Copy

Nothing short of an autism cure is promised by this hot new research paper.

Among many thousands of proteins that a neuron needs to make in order to function properly there is one called SHANK3 made from the gene shank3. (Note the customary writing: by consensus, a gene’s name is written using small caps and italicized, whereas the protein’s name that results from that gene expression is written with caps).

This protein is important for the correct assembly of synapses and previous work has shown that if you delete its gene in mice they show autistic-like behavior. Similarly, some people with autism, but by far not all, have a deletion on Chromosome 22, where the protein’s gene is located.

The straightforward approach would be to restore the protein production into the adult autistic mouse and see what happens. Well, one problem with that is keeping the concentration of the protein at the optimum level, because if the mouse makes too much of it, then the mouse develops ADHD and bipolar.

So the researchers developed a really neat genetic model in which they managed to turn on and off the shank3 gene at will by giving the mouse a drug called tamoxifen (don’t take this drug for autism! Beside the fact that is not going to work because you’re not a genetically engineered mouse with a Cre-dependent genetic switch on your shank3, it is also very toxic and used only in some form of cancers when is believed that the benefits outweigh the horrible side effects).

In young adult mice, the turning on of the gene resulted in normalization of synapses in the striatum, a brain region heavily involved in autistic behaviors. The synapses were comparable to normal synapses in some aspects (from the looks, i.e. postsynaptic density scaffolding, to the works, i.e. electrophysiological properties) and even more so in others (more dendritic spines than normal, meaning more synapses, presumably). This molecular repair has been mirrored by some behavioral rescue: although these mice still had more anxiety and more coordination problems than the control mice, their social aversion and repetitive behaviors disappeared. And the really really cool part of all this is that this reversal of autistic behaviors was done in ADULT mice.

Now, when the researchers turned the gene on in 20 days old mice (which is, roughly, the equivalent of the entering the toddling stage in humans), all four behaviors were rescued: social aversion, repetitive, coordination, and anxiety. Which tells us two things: first, the younger you intervene, the more improvements you get and, second and equally important, in adult, while some circuits seem to be irreversibly developed in a certain way, some other neural pathways are still plastic enough as to be amenable to change.

Awesome, awesome, awesome. Even if only a very small portion of people with autism have this genetic problem (about 1%), even if autism spectrum disorders encompass such a variety of behavioral abnormalities, this research may spark hope for a whole range of targeted gene therapies.

Reference: Mei Y, Monteiro P, Zhou Y, Kim JA, Gao X, Fu Z, Feng G. (Epub 17 Feb 2016). Adult restoration of Shank3 expression rescues selective autistic-like phenotypes. Nature. doi: 10.1038/nature16971. Article | MIT press release

by Neuronicus, 19 February 2016

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The FIRSTS: Betz pyramidal neurons (1874)

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Betz cell in the dog cortex. Copyright: RA Bergman, AK Afifi, PM Heidger, & MP D’Alessandro. Pic taken from here.

Bigger that Purkinje cerebellar neurons, the Betz pyramidal neurons (aka the giant pyramidal neurons) can have up to 100 micrometers in diameter. They are located in the fifth layer of the grey matter in the primary motor cortex. And they were discovered by a Ukrainian who did not receive the just place he deserves in the history of neuroscience, as most books on the subject ignore him. So let’s give him some attention.

Vladimir Alekseyevich Betz (1834–1894) was a professor of anatomy and a histologist at the Kiev University. Just like with Pavlov, sometimes there is nothing spectacular or weird or bizarre in the life of a great thinker. Betz was a child of a relatively wealthy family, went to good schools, then to Medical School, where he showed interest in the anatomy department. He continued his postgraduate studies in the West (that is Germany and Austria) after which he returned home where he got a position as a professor at his Alma Mater where he stayed until he died of heart problems at the age of 60.

Vladimir_Betz
Vladimir Alekseyevich Betz (1834 – 1894), License: PD

During his PhD, which was on the blood flow in the liver, Betz discovered an interest in histology. He was unsatisfied with the quality of the existing staining methods, so he worked for years to improve the fixation and staining methods of the brain tissue. His new methods allowed the cutting and preserving very thin slices and then he described what he saw. But Betz’s genius was in linking his cortical cytoarchitechtonic findings with physiological function, dividing the cortex into the motor and sensory areas. He also made revolutionary observations of the anatomical organization and development and various pathologies.

Original reference (which I did not find): Betz W (1874). Anatomischer Nachweis zweier Gehirncentra. Centralblatt für die medizinischen Wissenschaften. 12:578-580, 595-599.

Reference: Kushchayev SV, Moskalenko VF, Wiener PC, Tsymbaliuk VI, Cherkasov VG, Dzyavulska IV, Kovalchuk OI, Sonntag VK, Spetzler RF, & Preul MC (Jan 2012, Epub 10 Nov 2011). The discovery of the pyramidal neurons: Vladimir Betz and a new era of neuroscience. Brain, 135(Pt 1):285-300. doi: 10.1093/brain/awr276.  ArticleFREE FULLTEXT PDF

By Neuronicus, 17 December 2015

The FIRSTS: Axon description (1865)

Human medulla oblongata sectioned at the level of the olivary nuclei. Drawing by Deiters (1965). Original caption: Fig. 15. Durchschnitt der medulla oblongata des Menschen in der Höhe der Olive (OL). R.R Raphe, Hyi). Nervus hypoglossus. Vag. Nervus vagus, deren Kerne in V und H liegen, aber in der Zeichnung nicht feiner ausgeführt sind. Den Haupttlißil der Figur nimmt die Formatio reticularis ein mit ihren zerstreuten Ganglienzellen, und die Olive mit den zu ihr hinzutretenden Fasern des Stratum zonale; C.c crura cerebelli ad medullam oblongatam; P Pyramidenstrang.
Human medulla oblongata sectioned at the level of the olivary nuclei. Drawing by Deiters (1865). Original caption: “Fig. 15. Durchschnitt der medulla oblongata des Menschen in der Höhe der Olive (OL). R.R Raphe, Hyi). Nervus hypoglossus. Vag. Nervus vagus, deren Kerne in V und H liegen, aber in der Zeichnung nicht feiner ausgeführt sind. Den Haupttlißil der Figur nimmt die Formatio reticularis ein mit ihren zerstreuten Ganglienzellen, und die Olive mit den zu ihr hinzutretenden Fasern des Stratum zonale; C.c crura cerebelli ad medullam oblongatam; P Pyramidenstrang”.

In 1863, using the microscope, a german neuroanatomist from the University of Bonn by the name of Otto Friedrich Karl Deiters describes in exquisite detail the branch-like processes of the neuron (i. e. dendrites) and the long, single “axis cylinder” (i.e. axon). Deiters’ nucleus is named after him (the place where a good portion of the cranial nerve VIII ends).

The book with the findings is published in German, posthumously (in 1865), with preface and under the editorial guidance of Max Schultze, another famous German anatomist. I got the information from Debanne et al. (2011), which is nice review on axon physiology (my German is kindda rusty due to lack of use). But I got my hands on the original German book (see link below) and, like a kid that doesn’t know how to read yet, all I could do was marvel at the absolutely stunning drawings by OFK Deiters. Which are truly and unequivocally beautiful. See for yourself.

Neurons with axons and dendrites. Drawings buy Deiters (1865.)
Neurons with axons and dendrites. Drawings by Deiters (1865.)

Reference: Debanne D, Campanac E, Bialowas A, Carlier E, & Alcaraz G (April 2011). Axon physiology. Physiological Reviews, 91(2):555-602. doi: 10.1152/physrev.00048.2009. Article | FREE FULLTEXT PDF

Original citation: Deiters OFK (1865). Untersuchungen über Gehirn und Rückenmark des Menschen und der Säugethiere. Ed. Max Schultze, Braunschweig: Vieweg, 1865. doi: 10.5962/bhl.title.15270. Book | PDF

By Neuronicus, 24 October 2015

Making new neurons from glia. Fully functional, too!

NeuroD1 transforms glial cells into neurons. Summary of the first portion of the Guo et al. (2014) paper.
Fig. 1. NeuroD1 transforms glial cells into neurons. Summary of the first portion of the Guo et al. (2014) paper.

Far more numerous than the neurons, the glial cells have many roles in the brain, one of which is protecting an injury site from being infected. In doing so, they fill up the injury space, but they also prohibit other neurons to grow there.

Guo et al. (2015) managed to turn these glial cells into neurons. Functioning neurons, that is, fully integrated within the rest of the brain network! They did it in a mouse model of stab injury and a mouse model of Alzeihmer’s in vivo. Because a mouse is not a man, they also metamorphosized human astrocytes into functioning glutamatergic neurons in a Petri dish, that is in vitro.

It is an elegant paper that crossed all the Ts and dotted all the Is. They went to a lot of double checking in different ways (see Fig. 1) to make sure their fantastic claim is for real (this kind of double, triple, quadruple checking is what gets a paper into the Big Name journals, like Cell). Needles to say, the findings show a tremendous therapeutic potential for people with central nervous system injuries, like paralyses, strokes, Alzheimer’s, Parkinson’s, Huntington, tumor resections, and many many more. Certainly worth a read!

Reference: Guo Z, Zhang L, Wu Z, Chen Y, Wang F, & Chen G (6 Feb 2014, Epub 19 Dec 2013). In vivo direct reprogramming of reactive glial cells into functional neurons after brain injury and in an Alzheimer’s disease model. Cell Stem Cell, 14(2):188-202. doi: 10.1016/j.stem.2013.12.001. Article | FREE FULLTEXT PDF | Cell cover

By Neuronicus, 18 October 2015

I can watch you learning

Human Stereotaxic System. Photo credit: The Mind Project
Human Stereotaxic System. Photo credit: The Mind Project

Recording directly form the healthy living human brain has always been a coveted goal of many neuroscientists, thus bypassing the limitations of non-invasive techniques or animal work. But, understandably, nobody would seek or grant approval for inserting an electrode in the healthy living human brain, on moral and ethical grounds. The next best thing is to insert an electrode into the not so healthy living human brain.

Ison, Quiroga, & Fried (2015) got lucky and gained access to 14 patients with intractable epilepsy that had electrodes implanted in their brain to find where the seizure focus is (for possible surgical resection later on). Using these electrodes, they recorded the activity of single neurons within the medial temporal lobe (MTL, a brain area paramount for learning) while the patients performed some simple association tasks. First, they presented images of places, people, and animals to the patients to see “which (if any) of the recorded neurons responded to a picture” (p. 220). When they got a neuron responding to something, they rushed out, did some data and image processing, and after an hour they started the experiment. Which was showing the patient the picture to which the neuron responded to (e.g. Stimulus 1 = patient’s daughter) overimposed on a background that the neuron did not respond to (e.g. Stimulus 2 = the Eiffel tower). After one single trial (although there was some variability), the patients learned the associations (i.e. Stimulus 3 = daughter in front of Eiffel tower) and this learning was mirrored by how the neuron responded. Namely, the neuron increased its activity by 200% to 400% (counted in spikes per second) when shown the previously un-responded to image alone (i.e. Stimulus 2).

Excerpt from Fig. 5 from Ison, Quiroga, & Fried (2015).
Excerpt from Fig. 5 from Ison, Quiroga, & Fried (2015). “Average normalized neural activity (black squares) and behavioral responses (green circles) to the non-preferred stimulus as a function of trial number. Data were aligned to the learning time (relative trial number 0)”, i.e. when they showed the composite image between Stimulus 1 and Stimulus 2. “Note that the neural activity follows the sudden increase in behavioral learning”.

The authors recorded from over 600 neurons from various MTL regions, out of which 51 responded to a Stimulus 1. From these, only half learned, that is, they increased their activity when Stimulus 2 was shown. For the picky specialist, the cells were both Type 1 and Type 2 neurons, located 6 in the hippocampus, 4 in the entorhinal cortex, 11 in the parahippocampal cortex, and 1 in the amygdala. And the authors controlled for familiarity, attentional demands, and other extraneous variables (with some very fancy and hard to follow stats, I might add).

The paper settles an old psychology dispute. Do we learn an association gradually or at once? In other words, do we learn gradually that A and B occur together, or do we learn that the first time we are shown A and B together and the next trials serve just to refine and consolidate the new knowledge? Ison, Quiroga, & Fried (2015) data show that learning happens at once, in an all-or-none fashion.

Reference: Ison, M. J., Quian Quiroga, R., & Fried, I. (1 July 2015). Rapid Encoding of New Memories by Individual Neurons in the Human Brain. Neuron, 87(1): 220-30. doi: 10.1016/j.neuron.2015.06.016. Article | FREE PDF

By Neuronicus, 4 October 2015

The song of a fly… the courtship of another

Drosophila melanogaster image illustrating sexual dimorphism and mating behavior. Credit: TheAlphaWolf (Wikimedia Commons)
Drosophila melanogaster image illustrating sexual dimorphism and mating behavior. Credit: TheAlphaWolf (Wikimedia Commons)

Did you know that flies sing? True to the dictum that I just made up – ‘where is song, there is lust’ – it turns out not only that flies can sing, but they even have courtship songs! Granted, since they don’t have a larynx, the male flies sing by vibrating their wings in a certain way, which is unique to each fly species, and females listen with the feather-looking bit on top of their antennae, called arista. The behavior has generated enough research that a fairly hefty review about it has been published two years ago in Nature Reviews Neuroscience, pointing to a gene central to the male courtship circuitry and expressed only in the fly’s neurons, the fru gene (I bet it was called that way because when you make mutants you get fru/fru …).

Zhou et al. (2015) used a series of complicated experiments to successively activate or inhibit the neurons which express the fru gene, in order to identify the neural circuitry underlying hearing and processing the courtship songs. This circuitry is different in males and females, which makes sense since the serenading male expects different behaviors from his audience, depending on their sex; the listening males hurry to compete for the intended female and the females slow down and… listen carefully. Mind wondering: if I was the one serenading, wouldn’t I want to drive away the competitors, instead of drawing them in towards the object of my desire? Perhaps I want the competitors to also engage in courtship behavior so I can show off my wing vibrating prowess… Anyway, digression aside, in addition to figuring out which neuron does what, the authors managed to elicit courtship behavior in the listening males by optogenetically stimulating the 3rd and 4th order neurons in the newly identified circuit.

Besides being strangely interesting in itself, the research fills a gap in the understanding how courtship behavior is recognized, at least in fruit flies, which may be very useful information for other species as well, humans included.

Reference: Zhou, C., Franconville, R., Vaughan, A. G., Robinett, C. C., Jayaraman, V., & Baker, B. S. (21 September 2015). Central neural circuitry mediating courtship song perception in male Drosophila. Elife, 4:1-15. doi: 10.7554/eLife.08477. Article + FREE PDF

For the interested specialist, the MATLAB source code for analyzing calcium-imaging data can be found here.

By Neuronicus, 24 September 2015