Using a Scientifica Multiphoton Microscope for investigating retinal neurophysiology
Using standard fluorescence microscopy to visualise fluorescently labelled cells is not a viable option in retinal research, as the intense visible excitation light would cause substantial excitation of the photoreceptors, activating the entire circuitry of the retina and severely disrupting the experiment or rendering the tissue unresponsive to light.
In contrast, two-photon microscopy relies on light in the near-infrared spectral region (commonly over 800 nm), limiting the activation of photoreceptors by the excitation light. Thus, two-photon targeted recordings have become a central method in retinal research.
In each of the examples below, imaging experiments were carried out using a “first generation” Scientifica multiphoton microscope to answer the groups’ research questions. The Scientifica HyperScope or VivoScope systems could now perform similar or more advanced imaging experiments for retinal neurophysiology studies.
Horizontal or Vertical? How does the mouse retina help to assess an object’s orientation?
Researchers at the Feinberg School of Medicine identified two novel types of orientation selective retinal ganglion cells (OS RGCs) in the mouse retina.
These cells are highly selective for vertical or horizontal cardinal orientations, and their morphology and electrophysiology are beginning to give insights into the mechanisms through which mammals calculate orientation.
At the Bench: The High Definition family of retinal ganglion cells
Historically, the diverse group of ~40 retinal ganglion cells (RGCs) are divided into subtypes by either their distinct morphology or their ability to extract specific features from a visual scene. Subtypes that are labelled as “feature detectors” respond especially strongly or selectively to things such as local or global motion, the direction of motion, stimulus orientation, contrast or uniformity, or the presence of large or small objects.
Researchers identified three novel, small-receptive-field, non-direction selective ON-OFF retinal ganglion cells in the mouse retina through research efforts at Northwestern University. Each type has a feature detection profile that is individually tuned to size, speed, and object motion.
Visual receptive field mapping using filtered back projection
A paper published in The Journal of Physiology shows how filtered back projection (FBP), an algorithm often used for tomographic reconstruction (e.g. in CAT scans), can be used to map the spatial and temporal receptive fields (RFs) of retinal neurons. It also explains the advantages of using FBP over the traditional spike-triggered average (STA) method for mapping RFs.
Positively illuminating: a functional amacrine cell circuit in the retina
Neuroscientists have identified the role of a microcircuit in the mouse retina, where inhibition derived from a specific amacrine cell largely contributes to the spiking output of a specific retinal ganglion cell (RGC).
The paper, from principal investigator Dr Greg Schwartz, provides evidence for the direct synaptic connectivity between CRH-1 amacrine cells and the Suppressed-by-Contrast SbC RGC, as well as for a functional role of this circuit within the intact retina.
A multiphoton imaging system with an extended scan head designed specifically for performing in vivo imaging. Ideal for larger in vivo samples, linear or spherical treadmills, large stereotaxic frames or other virtual reality set-ups.
Related SciMethod: Visual Stimulation of Retinal Explants on a Standard Multiphoton Microscope
This application note describes two approaches to integrating visual stimulation of the retina into a two-photon microscope.