Ultrasound tracks odor representation in the brain

A new ultrasound imaging technique has provided the first ever in vivo visualization of activity in the piriform cortex of rats during odor perception. This deep-seated brain structure plays an important role in olfaction, and was inaccessible to functional imaging until now. This work also sheds new light on the still poorly known functioning of the olfactory system, and notably how information is processed in the brain. This study is the result of a collaboration between the team led by Mickael Tanter at the Institut Langevin (CNRS/INSERM/ESPCI ParisTech/UPMC/Université Paris Diderot) and that led by Hirac Gurden in the Laboratoire Imagerie et Modélisation en Neurobiologie et Cancérologie (CNRS/Université Paris-Sud/Université Paris Diderot). Their findings are published in NeuroImage dated July 15, 2014.

How can the perception of the senses help represent the external environment? How, for example, does the brain process food or perfume related olfactory data? Although the organization of the olfactory system is well known it is similar in organisms ranging from insects to mammals its functioning remains unclear. To answer these questions, the scientists focused on the two brain structures that act as major olfactory relays: the olfactory bulb and the piriform cortex. In the rat, the olfactory bulb is located between the eyes, just behind the nasal bone. The piriform cortex, meanwhile, is deep seated in the brain of rodents, which made it impossible to obtain any functional images in a living animal until now.

Yet the neurofunctional ultrasound imaging technique developed by Mickael Tanter’s team, called fUS (functional Ultrasound), allows the monitoring of neuronal activity in the piriform cortex. It is based on the transmission of ultrasonic plane waves into the brain tissue. After data processing, the echoes returned by the structures crossed by these waves can provide images with unequalled spatial and temporal resolution: 80 micrometers and a few tens of milliseconds. The contrast on these images is due to variations in the brain’s blood flow. Indeed, the activity of nerve cells requires an input of energy: it is therefore coupled to an influx of blood into the zone concerned. By recording volume variations in the blood vessels irrigating the different brain structures, it is therefore possible to determine the location of activated neurons.

Several imaging techniques, such as MRI, are already based on the link between blood volume and neuronal activity. But fUS offers advantages in terms of cost, ease of use and resolution. Furthermore, it provides easier access to the deepest structures that are often located several centimeters beneath the cranium. The recordings performed by Hirac Gurden’s team using this technique made it possible to observe the spatial distribution of activity within the olfactory bulb. When an odor was perceived, blood volume increased in clearly defined areas: each odor thus corresponded to a specific pattern of activated neurons.

In addition to these findings, and for the first time, the images revealed an absence of spatial distribution in the piriform cortex. At this level, two different odors triggered the same activation throughout the region. The cellular mechanisms responsible for the disappearance of a spatial signature are not yet clearlydefined, but these findings lead to the formulation of several hypotheses. The piriform cortex could be a structure that serves not only to process olfactory stimuli but rather to integrate and memorize different types of data. By making abstraction of the strict odor induced patterns, it would be possible to make associations and achieve a global concept. For example, based on the perception of the hundreds of odorant molecules found in coffee, the piriform cortex would be able to recognize a single odor, that of coffee.

This work opens new perspectives for both imaging and neurobiology. The researchers will now be focusing on the effects of learning on cortical activity in order to elucidate its role and the specificities of the olfactory system.

pomme banane

Laser bioprinting in Bordeaux : an innovative approach

In recent years, 3D printing has developed in the area of health. Custom medical devices and prostheses were the first applications for this new technology. In 2011, for example, the first prosthesis (a titanium jaw) made with the help of 3D printing was implanted. Two years later, a 3D printed cranium (the largest ever placed) was implanted into a 22-year-old woman in the Netherlands.

In addition to these medical devices made of inert materials, researchers took on a challenge of an entirely different nature : bioprinting involves printing living cellular materials!

In contrast to traditional 3D printing, bioprinting involves consideration of a 4th dimension: the time dimension, in which the printed cells assemble themselves, migrate and differentiate autonomously to form functional tissues.

ModuLAB 1

Bioprinting 3D © Inserm/ Guillemot, Fabien – Alphanov / Lescieux, Ludovic

Laser bioprinting in Bordeaux, an innovative approach

One of the goals of the laboratory is to develop laser and microfabrication technologies with the aim of printing tissues in vitro and in vivo. The researchers in the laboratory were pioneers in Europe, developing laser-assisted bioprinting from 2005. This Inserm/University of Bordeaux joint research unit is one of a very few worldwide to use this process. The objective of Fabien Guillemot’s team is therefore not only to position cells in 3D, but to define and model the self-assembly dynamic of the printed cells.

What are the results using the laser approach?

In the laboratory, bioprinting employs the principles of 3D printing to assemble the components of biological tissues (such as the cells and the extracellular matrix) layer by layer in digitally designed predefined patterns.

Laser-assisted bioprinting enables the manufacture of complex tissues with the help of printing using bioinks with cell concentrations close to physiological conditions, with a high degree of resolution (micron scale, pL volume) and a high operating speed (.> 10,000 droplets per second).

“In the area of bioprinting, laser technology offers the highest resolution,” explains Fabien Guillemot, Inserm Research Fellow.

Since 2005, the research team has succeeded in printing different structures and cell types with multiple layers of keratinocytes (cells of the superficial layer of the skin and appendages—nails and body and head hair) and collagen.

Impression de peau

Impression de peau réalisée en juin 2014
© Ludovic Lescieux Alphanov / Fabien Guillemot Inserm.

Printed cells are viable (97% viability after 6 h), and the researchers confirmed that bioprinting did not affect cell differentiation in the case of human adult stem cells.

At the moment, researchers are working on printing corneal and skin tissues in order to meet the needs of regenerative medicine, pharmacology, cosmetics, etc.

At the same time, the research team also conducts in vivo experiments in mice. In 2010 it succeeded in printing mesenchymal stem cells in the bone of live mice. The next step will involve testing computer-aided surgery which would allow in vivo printing of tissues directly where required.

What is the outlook for tomorrow?

The challenge of bioprinting remains the production of functional tissues with the aim of creating:

  • Here and now….Predictive models that reproduce the physiology of healthy human tissues or diseased tissues, enabling the more predictive testing of drugs, components and candidate drugs. These physiological models will be used in the pharmaceutical field. (For cosmetic applications, the overall market for alternative methods has been estimated at €1 billion in 2015 (Source: Transparency Market Research), with an annual growth of 13.1%.)

  • In the next 3-5 years…Individualised tissues, made using patient cells, that allow in vitro selection of treatment based on these tissues, and development of personalised treatment solutions. Fabien Guillemot’s team hopes to include bioprinting in the developments of the new Cancer Plan concerning individualised medicine.

  • In the next 7-10 years…Implantable tissues for regenerative medicine. The development and manufacture of biological tissues represent major socioeconomic challenges. The market for tissue engineering was valued at $15 billion in 2014, and should double by 2018 (source: MedMarket Diligence, LLC.). Moreover, because of the increase in life expectancy, and in the incidence of major diseases such as cancer and diabetes, the number of people waiting for an organ transplant is constantly increasing (51,000 people in Europe in 2013).

Despite advances in research, it is not presently possible to print functioning organs. 

“Once researchers are able to create functional tissues, they will then be able to modify these tissues to improve them. Ethical debate will be needed to determine the extent to which tissue modification is possible, and for what purposes,” emphasises the researcher.