New Optical and Genetic Tools to Help Distinguish Brain Cell Types

The search for correlations between structure and function in the brain continues (see previous post “Brain Research Using Online Data Repositories: Brain Cell Shape and Function“). The line between structure and function has blurred as brain scientists distinguish brain cells based on gene expression and proteins in addition to shape, connectivity and electrical response properties.

A new study from the laboratory of Clay Reid uses a technique called two-photon calcium imaging and new innovations using optical and genetic tools that enable them to identify the same cells in processed brain tissue that they recorded electrical activity from when the animal was alive.

The paper “Broadly Tuned Response Properties of Diverse Inhibitory Neuron Subtypes in Mouse Visual Cortex” was published in the September 9, 2010 issue of Neuron.

In this paper the authors describe using imaging in the live animal to study electrical signaling in brain cells. They injected a florescent marker into the area of the brain they were studying so that after they removed the brain they could locate and identify the same set of cells that they were studying in the live animal.

They were able to distinguish between excitatory and inhibitory cells by using a genetically manipulated line of mice whose inhibitory cells all show up under the microscope when a specific label is used. They then focused on distinguishing subtypes of inhibitory cells using labels that they applied to the brain after its removal from the mouse. These labels find specific peptides or proteins and bind to them.

While the mice were alive the investigators recorded changes in calcium concentration in these cells due to the presentations of light patterns to their eyes. Bars of light were presented in different orientations. Also gratings were presented.

The team found that the subtypes of inhibitory cells they looked at had diverse characteristics but very similar visual response properties. In contrast, excitatory cells (pyramidal neurons) have similar characteristics but more diverse visual response properties.

They conclude that “… excitatory neurons must receive sparser or more selective inputs to yield a preferred orientation that is independent of the local average.” However, another possibility is that both excitatory and inhibitory cells receive the same input but, the early arrival of an excitatory cells signal in the preferred orientation is expressed while the later signals arriving in the non-preferred orientations are suppressed by the inhibitory cells (see Wiggling Whiskers: Directional Tuning).




Other related blog posts:

Brain Research Using Online Data Repositories: Brain Cell Shape and Function

Wiggling Whiskers: Directional Tuning