Zebrafish

An MEA of 64 electrodes embedded in the substate at the bottom of a well.

Neurons attach to the array and form a network. The microelectrodes detect the action potentials fired as well as their propagation across the network.

 

Brain waves in a dish

Neurons communicate with other cells via electrochemical signals. Many neural cell types form cellular networks, and MEAs allow us to capture and record the electrical activity that propagates through these networks.

Neurons fire action potentials that are detected by adjacent electrodes as extracellular spikes. As the network matures, neurons often synchronize their electrical activity and may exhibit network bursts, where neurons repeatedly fire groups of spikes over a short period of time.

The MEA detects each cell's activity, as well as the propagation of the activity across the network, with spatial and temporal precision. Patterns as complex as EEG-like waveforms, or "brain waves in a dish", can be observed. Axion's MEA assay captures key features of neural network behavior as functional endpoints - activity, synchrony, and network oscillations.

Action potentials are the defining feature of neuron function. High values indicate frequent action potential firing and low values indicate the neurons may have impaired function.

Synapses are functional connections between neurons. Synchrony reflects the prevalence and strength of synaptic connections, and thus how likely neurons are to generate action potentials simultaneously on millisecond time scales.

Network oscillations, or network bursting, as defined by alternating periods of high and low activity, are a hallmark of functional networks with excitatory and inhibitory neurons. Oscillation is a measure of how the spikes from all of the neurons are organized in time.

Do more with multiwell

Axion BioSystems offers multiwell plates, ranging from 6 to 96 wells, with an MEA embedded in the bottom of each well. Multiwell MEA plates allow you to study complex neural biology in a dish, from a single cell firing to network activity, across many conditions and cell types at once.

Optogenetics: Using light to control cells

Optogenetics is a technique that involves the use of light to control cell function. Cells are first genetically modified to express light-sensitive ion channels, called opsins. Then, light can be used to activate the opsin. The most well-known opsins are light-gated ion channels that can control the excitability of the cell membrane. When activated by the opsin-specific wavelength of light, the channels open allowing ions to flow across the cell membrane to either excite or inhibit the cell. Optogenetics enables precise control over a targeted cell population.

Many opsins, many options

Since the first microbial opsin was introduced into mammalian neurons in 2005, many different opsins have been used to control the excitability of electroactive cells such as neurons and cardiomyocytes. Each opsin is sensitive to a specific wavelength range, or color of light and induces a precise biological event.

Channelrhodopsin (ChR2), for example, is activated by blue light. When ChR2 opens, positive cations (like sodium and calcium), flow into the cell, depolarizing or exciting the cell. In contrast, halorhodopsin and archaerhodopsin both inhibit cell excitability by hyperpolarizing the cell in response to yellow or green light, respectively. With optogenetics, you can turn on and off cells like a light switch.

The timing of these light-activated events is fast, facilitating highly precise control. First generation opsins, such as channelrhodopsin, open and close in milliseconds, ideal for kicking off an action potential. Second generation opsins have fined tuned kinetics for even faster, more precise control or slower, longer-lasting inhibition. For example, step-function opsins stay open until another pulse of light switches them off.

Optogenetics can precisely control which cells are turned on or off by employing different gene promoters for opsin expression. Opsins can be expressed in all neurons or used to control specific subpopulations. Unlike electrical stimulation, which excites all nearby cells, optical stimulation can be finely targeted to the cells expressing the opsins responsive to a narrow band of light wavelengths.

In summary, optogenetics is a powerful toolbox for precise control over targeted cell populations at fast time scales. Superior spatial and temporal control, reversibility, and easy stimulus delivery make exploring complex biology simpler than ever before.

More than just ion channels

As the field has advanced, opsins have been used to control more than just ion flow. Light-activated gene expression with light-inducible transcription factors can control the proteins made by cells. The combination of optogenetics with CRISPR provides even greater control over CRISPR/Cas9 gene editing.

Opsins have also been incorporated into many biochemical and intracellular signaling pathways to control key protein functions. MAPK and PI3K pathways, Rho family GTPase activation, apoptosis, and protein trafficking can now all be precisely controlled by light.

Shining light in vitro

Sophisticated biology like optogenetics demands sophisticated technology to explore it. In vitro technology relied on single wavelength lasers and custom lab-specific tools while many in vivo technologies were quickly developed for optical stimulation. The Lumos Optical Stimulation system is the first-of-its-kind multiwell optical stimulator with the ability to deliver up to four wavelengths of light per well with microsecond precision. From controlling the excitability of your neurons to pacing the beating of your cardiomyocytes, discover how the Lumos and optogenetics can revolutionize your assay.