Neuronal growth cones respond to laser-induced axonal damage

Minocycline Increases in-vitro Cortical Neuronal Cell Survival after Laser Induced Axotomy

Background

Antibiotic therapies targeting multiple regenerative mechanisms have the potential for neuroprotective effects, but the diversity of experimental strategies and analyses of non-standardised therapeutic trials are challenging. In this respect, there are no cases of successful clinical application of such candidate molecules when it comes to human patients.

Methods

After 24 hours of culturing, three different minocycline (Sigma-Aldrich, M9511, Germany) concentrations (1 µM, 10 µM and 100 µM) were added to the primary cortical neurons 15 minutes before laser axotomy procedure in order to observe protective effect of minocycline in these dosages.

Results

Here, we have shown that minocycline exerted a significant neuroprotective effect at 1 and 100μM doses. Beyond confirming the neuroprotective effect of minocycline in a more standardised and advanced in-vitro trauma model, our findings could have important implications for future studies that concentrate on the translational block between animal and human studies.

Conclusion

Such sophisticated approaches might also help to conquer the influence of human-made variabilities in critical experimental injury models. To the best of our knowledge, this is the first study showing that minocycline increases in-vitro neuronal cell survival after laser-axotomy.

Role of extrinsic mechanical force in the development of the RA-I tactile mechanoreceptor

Rapidly adapting type I (RA-I) mechanoreceptors play an important role in sensing the low-frequency vibration aspects of touch. The structure of the RA-I mechanoreceptor is extremely complex regardless of its small size, limiting our understanding of its mechanotransduction. As a result of the emergence of bioengineering, we previously proposed an in vitro bioengineering approach for RA-I receptors to overcome this limitation. Currently, the in vitro bioengineering approach for the RA-I receptor is not realizable given the lack of knowledge of its morphogenesis. This paper demonstrates our first attempt to interpret the cellular morphogenesis of the RA-I receptor. We found indications of extrinsic mechanical force nearby the RA-I receptor in the developing fingertip. Using a mechanical compression device, the axon of dorsal root ganglion (DRG) neurons buckled in vitro into a profile that resembled the morphology of the RA-I receptor. This work encourages further implementation of this bioengineering approach in tactile receptor-related research.

Modulation of Neural Network Activity through Single Cell Ablation: An in Vitro Model of Minimally Invasive Neurosurgery

The technological advancement of optical approaches, and the growth of their applications in neuroscience, has allowed investigations of the physio-pathology of neural networks at a single cell level. Therefore, better understanding the role of single neurons in the onset and progression of neurodegenerative conditions has resulted in a strong demand for surgical tools operating with single cell resolution. Optical systems already provide subcellular resolution to monitor and manipulate living tissues, and thus allow understanding the potentiality of surgery actuated at single cell level. In the present work, we report an in vitro experimental model of minimally invasive surgery applied on neuronal cultures expressing a genetically encoded calcium sensor. The experimental protocol entails the continuous monitoring of the network activity before and after the ablation of a single neuron, to provide a robust evaluation of the induced changes in the network activity. We report that in subpopulations of about 1000 neurons, even the ablation of a single unit produces a reduction of the overall network activity. The reported protocol represents a simple and cost effective model to study the efficacy of single-cell surgery, and it could represent a test-bed to study surgical procedures circumventing the abrupt and complete tissue removal in pathological conditions.

Rat embryonic hippocampus and induced pluripotent stem cell derived cultured neurons recover from laser-induced subaxotomy

Axonal injury and stress have long been thought to play a pathogenic role in a variety of neurodegenerative diseases. However, a model for studying single-cell axonal injury in mammalian cells and the processes of repair has not been established. The purpose of this study was to examine the response of neuronal growth cones to laser-induced axonal damage in cultures of embryonic rat hippocampal neurons and induced pluripotent stem cell (iPSC) derived human neurons. A 532-nm pulsed [Formula: see text] picosecond laser was focused to a diffraction limited spot at a precise location on an axon using a laser energy/power that did not rupture the cell membrane (subaxotomy). Subsequent time series images were taken to follow axonal recovery and growth cone dynamics. After laser subaxotomy, axons thinned at the damage site and initiated a dynamic cytoskeletal remodeling process to restore axonal thickness. The growth cone was observed to play a role in the repair process in both hippocampal and iPSC-derived neurons. Immunofluorescence staining confirmed structural tubulin damage and revealed initial phases of actin-based cytoskeletal remodeling at the damage site. The results of this study indicate that there is a repeatable and cross-species repair response of axons and growth cones after laser-induced damage.

Laser microbeam targeting of single nerve axons in cell culture

By focusing a laser with short pulses to a diffraction-limited spot, single nerve axons can be precisely targeted and injured. Subsequent repair can be analyzed using various imaging and biochemical techniques to understand the repair process. In this chapter, we will describe a robotic laser microscope system used to injure nerve axons while simultaneously observing repair using phase and fluorescence microscopy. We provide procedures for controlled laser targeting and an experimental approach for studying axonal repair in embryonic rat hippocampus neurons.

Loop formation and self-fasciculation of cortical axon using photonic guidance at long working distance

The accuracy of axonal pathfinding and the formation of functional neural circuitry are crucial for an organism to process, store, and retrieve information from internal networks as well as from the environment. Aberrations in axonal migration is believed to lead to loop formation and self-fasciculation, which can lead to highly dysfunctional neural circuitry and therefore self-avoidance of axons is proposed to be the regulatory mechanism for control of synaptogenesis. Here, we report the application of a newly developed non-contact optical method using a weakly-focused, near infrared laser beam for highly efficient axonal guidance, and demonstrate the formation of axonal loops in cortical neurons, which demonstrate that cortical neurons can self-fasciculate in contrast to self-avoidance. The ability of light for axonal nano-loop formation opens up new avenues for the construction of complex neural circuitry, and non-invasive guidance of neurons at long working distances for restoration of impaired neural connections and functions.

Highly effective photonic cue for repulsive axonal guidance

In vivo nerve repair requires not only the ability to regenerate damaged axons, but most importantly, the ability to guide developing or regenerating axons along paths that will result in functional connections. Furthermore, basic studies in neuroscience and neuro-electronic interface design require the ability to construct in vitro neural circuitry. Both these applications require the development of a noninvasive, highly effective tool for axonal growth-cone guidance. To date, a myriad of technologies have been introduced based on chemical, electrical, mechanical, and hybrid approaches (such as electro-chemical, optofluidic flow and photo-chemical methods). These methods are either lacking in desired spatial and temporal selectivity or require the introduction of invasive external factors. Within the last fifteen years however, several attractive guidance cues have been developed using purely light based cues to achieve axonal guidance. Here, we report a novel, purely optical repulsive guidance technique that uses low power, near infrared light, and demonstrates the guidance of primary goldfish retinal ganglion cell axons through turns of up to 120 degrees and over distances of ∼90 µm.

Investigation of nerve injury through microfluidic devices

Traumatic injuries, both in the central nervous system (CNS) and peripheral nervous system (PNS), can potentially lead to irreversible damage resulting in permanent loss of function. Investigating the complex dynamics involved in these processes may elucidate the biological mechanisms of both nerve degeneration and regeneration, and may potentially lead to the development of new therapies for recovery. A scientific overview on the biological foundations of nerve injury is presented. Differences between nerve regeneration in the central and PNS are discussed. Advances in microtechnology over the past several years have led to the development of invaluable tools that now facilitate investigation of neurobiology at the cellular scale. Microfluidic devices are explored as a means to study nerve injury at the necessary simplification of the cellular level, including those devices aimed at both chemical and physical injury, as well as those that recreate the post-injury environment.

Neuronal beacon

The controlled navigation of the axonal growth cone of a neuron toward the dendrite of its synaptic partner neuron is the fundamental process in forming neuronal circuitry. While a number of technologies have been pursued for axonal guidance over the past decades, they are either invasive or not controllable with high spatial and temporal resolution and are often limited by low guidance efficacy. Here, we report a neuronal beacon based on light for highly efficient and controlled guidance of cortical primary neurons.

The formation of actin waves during regeneration after axonal lesion is enhanced by BDNF

During development, axons of neurons in the mammalian central nervous system lose their ability to regenerate. To study the regeneration process, axons of mouse hippocampal neurons were partially damaged by an UVA laser dissector system. The possibility to deliver very low average power to the sample reduced the collateral thermal damage and allowed studying axonal regeneration of mouse neurons during early days in vitro. Force spectroscopy measurements were performed during and after axon ablation with a bead attached to the axonal membrane and held in an optical trap. With this approach, we quantified the adhesion of the axon to the substrate and the viscoelastic properties of the membrane during regeneration. The reorganization and regeneration of the axon was documented by long-term live imaging. Here we demonstrate that BDNF regulates neuronal adhesion and favors the formation of actin waves during regeneration after axonal lesion.