In our News post this week, we recommend reading this detailed review article on the current techniques for investigating the brain extracellular space. In this paper, Tønnesen’s lab provides an introduction to in vitro and in vivo current neuroscience lab methods such as point-source diffusion measurement, electron microscopy, magnetic resonance imaging, widefield fluorescence microscopy, scanning fluorescence microscopy, and super-resolution fluorescence microscopy. These techniques are mainly based on optical imaging and electrical recordings.
This multiplication of methods has offered scientists the opportunity to diversify their approach to a specific scientific question. This article highlights the strengths and weaknesses of each technology. In order to diversify the observations of a given sample, the authors recommend combining several levels of study and methodology to broaden the project perspectives.
Overview of the Current Techniques for Investigating the Brain Extracellular Space - Soria et al.
Presenting our latest addition: the 3D accelerometer!
Connecting behavioral observations to nervous system activity has become increasingly important. Diverse technologies are available for measuring the neuronal activity in freely moving rodents, such as in vivo imaging – e.g. fiber photometry – and electrophysiology recordings. Additionally, it is equally crucial to precisely detect, quantify, and classify animal behaviors.
The 3D accelerometer is used to detect movement onsets and discern specific behaviors, such as rearing. This tool allows head movement measurements at high temporal resolution and along 3 axes independently of each other. Lightweight and compact, the sensor board is easily mounted and can be carried by both mice and rats.
3D accelerometer device, including the sensor board and the sensor cable with connectors
An example of accelerometer measurements of head pitch and roll can be found in this article:
Retrograde tracing, optogenetic manipulation, fiber photometry, cell-specific electrophysiology… Neuroscientists benefit from an increasingly wide range of tools to image and study the activity of neuronal populations. All these experiments rely on the same crucial step: intracerebral surgery. These procedures require specific equipment, from the stereotaxic instruments to the anesthesia methods.
Traditionally carried out through injection, the anesthesia is nowadays mostly performed with the inhalation of anesthetic gas, thanks to its rapid induction and limited recovery time. However, surgical procedures can sometimes be challenging when they are conducted on neonatal mice. A team from Cambridge (Hinze Ho et al.) has decided to tackle this issue by developing its own protocol to control the anesthesia of P0-2 mice. Combined with the design of an anesthetization mould, this method ensures an improved recovery for the rodents.
Access to the research article following this link: https://doi.org/10.1016/j.jneumeth.2020.108824.
Description of the surgery procedure - Hinze Ho et al.
Two-photon microscopy has revolutionized the ability to image neural activity in the brain of a living animal. Compared to single-photon microscopy, this technique allows for targeted excitation of small volumes in deep tissue. Moreover, the two-photon technique provides tissue penetration up to 800-1000 μm.
As powerful as it is, the imaging depth of a stand-alone two-photon microscope does not allow for deep brain region imaging. One technique used to image deeper is to couple the two-photon microscope with a gradient index (GRIN) lens. Implanted in the tissue, the GRIN lens allows the user to record from deep areas through long working distance objectives.
Even though two-photon GRIN lens-coupled imaging allows for optical sectioning and 3D imaging, this technique has limitations regarding axial scanning speed and contrast. By adding a tunable acoustic GRIN (TAG) lens to their setup, Chien et al. designed a new system allowing in vivo imaging of neurons in deep mouse brain areas with high-contrast and high-temporal resolution. The publication is available on bioRxiv following this link https://www.biorxiv.org/content/10.1101/2020.09.19.304675v1.
In vivo functional imaging of neuronal activity from SCN of a head-fixed anesthetized mouse - Chien et al. 2020
Dopamine is a neurotransmitter involved in key functions of the brain, e.g. motor control, reward, arousal, or motivation. To better understand the modulation of dopamine, it is fundamental to benefit from tools allowing both the manipulation of neuronal circuits and the recording of fluorescent signals in the brain, particularly in freely moving animals.
To perform such experiments, it is recommended that optogenetic actuators and imaging sensors spectra do not overlap. Therefore, expanding the fluorescent indicators palette is the key to successful multi-color imaging experiments.
In this new Nature Method article, Patriarchi et al. designed yellow-shifted and red-shifted dopamine sensors. Following their development of dLight1, a green fluorescent protein-based DA sensor, the team created YdLight1 – 525nm emission peak - and RdLight1 – 588nm emission peak. Exciting work!
More information can be found following this link: https://doi.org/10.1038/s41592-020-0936-3.
There was a long time ago when the first brain signal was recorded. Since then science has shown multiple ways to record brain activity in realtime. Somehow the public was shocked when Neuralink has demonstrated this last week. Probably because of Elon Musk the co-founder of Neuralink. Media follows Elon Musk's every step and big announcements. Proving that the implants work was a big step for Neuralink, although the technique was a long time ago described.
Another fascinating article from Janelia Research Campus in the Current Issue of Nature Methods. Dr. Lavis and his team introduced a new group of red shifted dye called 'Janelia Fluor' (JF) group. They outlined a general rubric that directly correlates the lactone–zwitterion equilibrium constant (KL–Z) to performance in biological environments. They compared a series of JF rhodamines with different fluorophoric systems. They developed a rubric to relate the performance of simple rhodamine dyes to a single parameter, KL–Z (Figure below), and discovered an inverse correlation between KL–Z and λabs. They hope these new findings help us to design fine-tuned dyes for specific biological applications. Such a great study!
Phenomenological plot categorizing the properties of different dyes based on KL–Z (left) and plot of KL–Z vs. λabs for JF dyes and general tuning strategies for dyes with short or long λabs.
The CAJAL Advanced Neuroscience Training Programme represents commitment by the five partner institutions FENS, IBRO, the Gatsby Charitable Foundation, University of Bordeaux and the Champalimaud Foundation, which offers state-of-the-art hands-on training courses in neuroscience.
This year the programme is between the 9-27th of November in Bordeaux, France. The original deadline was on the 27th of July, but due to the Covid virus the training programme is still open until the 1st of September 2020.
This course aims to bring students up-to-date with the most recent developments in this exciting and fundamental field of neuroscience research. The focus will be on the advanced experimental approaches that are available today for the dissection of neural circuit connectivity and activity in various animal models (mouse, fly, zebrafish).
The faculty will consist of international experts in their respective fields, discussing fundamental concepts and their own research, introducing methods relevant for neural circuit research, and providing hands-on projects. Students will perform experimental projects to apply these methods to scientific problems, they will learn how to analyze acquired data, and they will discuss strengths and limitations of the various techniques.
Electric foot shock is a complex stressor with both physical and emotional components. It has been employed as an important tool to develop diverse animal models in the field of psychopharmacology. Animals generally do not habituate to foot shocks in comparison to other stressors, including loud noise, bright light, and hot and cold temperatures. Additionally, it offers an experimental advantage of control over intensity and duration; therefore, by varying its application parameters, different disorder models have been created.
Supertech has a wide range of variety of tools for experimenting with foot shock paradigms. AC Shocker is a handy tool in any laboratory which studies associational learning with stressors. Its internal circuitry is based on a constant current generator operating on the mains frequency. The current generator is simplified, but the safety level of this equipment is as good as of the DC Shocker. The current range at the output: 0.05 to 2 mA, which is enough for all acceptable shocking methods for mice and rats. 10-turn helical potentiometer helps to adjust the output current with a great resolution to optimize the level of the shocking current. Manual or computer-controlled with TTL H-level is activation.
An interesting article was recently published in Elife journal about microglia calcium signaling. These cells are playing a crucial role in brain defense against internal and external hazards. Previously, they were mainly investigated in situ, but Dr. Wu and his colleagues demonstrated nice experiments in vivo in awake mice. They used multiple GCaMP6 variants targeted to microglia, two-photon imaging and Neurotar Air table for in vivo imaging. They showed microglia increased microglial process calcium signaling during hyperactive shifts in neuronal activity (kainate status epilepticus and CaMKIIa Gq DREADD activation).
Summary of findings and observed relationship between neuronal activity and microglial calcium signaling.
For more information: https://elifesciences.org/articles/56502