Imaging the Repair Potential of Cortical Neuronal Transplantation In Vivo

Michael Stryker, Ph.D.

University of California, San Francisco, San Francisco, CA
Website

Grant Program:

David Mahoney Neuroimaging Program

Funded in:

December 2005, for 2 years

Funding Amount:

$100,000

Lay Summary

Will Transplanted Brain Cells Function Like the Cells They Have Replaced?

This study will determine the feasibility of using cellular imaging in mice to determine whether embryonic brain cells that are transplanted into the cerebral cortex integrate into neural networks and functionally replace the brain cells that have died, or at least help to reorganize the neural networks. If feasibility is established, this imaging method could be used to develop refinements for improving transplantation therapy.

Inhibitory neurons normally suppress excessive brain activity. They are selectively damaged or killed in several brain diseases, such as epilepsy and prion disease (e.g., Creutzfeldt-Jacob disease). Recent research has demonstrated that new brain cells can be generated, but inhibitory neurons cannot be sufficiently generated in the cerebral cortex to offset the loss of these activity-suppressing cells. Transplantation of inhibitory neurons from a region of the embryonic brain where they develop, called the “medial ganglionic eminence,” is a promising therapeutic alternative. A major question, however, is whether or not the transplanted cells will integrate into the neural networks of the cells that they are replacing, or whether the transplanted cells will at least help to reorganize these networks into newly functioning neural circuits.

The researchers previously showed that normally functioning inhibitory neurons are crucial for enabling the visual cortex to reorganize its responses and connections as result of experience. If inhibitory neurons are transplanted into mice that have been bred to have insufficient numbers of these brain cells, the transplanted cells may be able to restore brain plasticity (the ability to form new connections) in these mice. As a first step towards determining whether this is the case, the investigators will transplant young neurons from the medial ganglionic eminence of embryonic mice into the visual cortex of the adult mouse. Then the researchers will use two-photon cellular imaging to assess the transplanted cells’ integration into brain tissue. If so, this will pave the way for further studies to determine whether the transplanted cells make functionally normal connections.

Significance: If successful, this research approach could lead to improved methods for developing and evaluating transplantation therapies for epilepsy and similar diseases that deplete inhibitory brain cells.

Abstract

Imaging the Repair Potential of Cortical Neuronal Transplantation In Vivo

This project will take advantage of newly developed imaging methods for measuring neuronal structure and function in vivo to determine whether young neurons extracted from the medial ganglionic eminence (MGE), the embryonic source of cortical inhibitory neurons, can assume the function of their native counterparts when they are transplanted into adult visual cortex. Using 2-photon optical microscopy, we will identify individual neve cells in the living brain as native or transplanted and will simultaneously record their activity. We will then test whether transplanted MGE cells acquire inputs that endow them with function activity similar to that of their native counterparts. The acquisition of normal visual response properties by the transplanted neurons will be a sensitive indicator of their functions integration.

Hypothesis

Hypothesis:
This proposal aims to examine in vivo whether young neurons extracted from the medial ganglionic eminence (MGE), the embryonic source of cortical inhibitory neurons, can acquire some of the properties of their native counterparts when they are transplanted into adult visual cortex. Combining recent advances in optical microscopy to image the structure and function of identified native and transplanted neurons in vivo, we will test the hypothesis that transplanted cells acquire inputs that endow them with functional activity similar to that of their native counterparts.

Goals:
We will transplant young neurons from the MGE into adult visual cortex and assess their functional integration into the host tissue using 2-photon cellular imaging in vivo. Distinct labels for donor and native MGE-derived cells, together with a novel imaging method for simultaneously recording visual responses from large numbers of these cells, will allow us to compare responses of host and transplanted populations to test the hypothesis.

Methods:
We will transplant inhibitory neuronal precursors from the embryonic brain into the primary visual cortex of the adult mouse, which is an excellent context in which to probe the integration of transplanted neurons into host circuits because the wiring and function of visual cortex are extensively characterized. To determine whether transplanted cells acquire meaningful synaptic inputs, we will compare the visually evoked responses of transplanted cells to their native counterparts. We will label nearly all the neurons within a 300 µm wide sphere using the high affinity calcium dye Oregon Green BAPTA-1-AM, and assess responses using -photon laser scanning microscopy.

Selected Publications

Cang J.C., Renteria R.C., Kaneko M., Liu X., Copenhagen D.R., and Stryker M.P. Development of precise maps in visual cortex requires patterned spontaneous activity in the retina. Neuron. 2005 Dec 8;48(5):797-809 .

Hensch, T.K. and Stryker, M.P. Columnar Architecture Sculpted by GABA Circuits in Developing Cat Visual Cortex. Science. 2004 Mar 12;303(5664):1678-81.

Kalatsky V.A. and Stryker M.P. New paradigm for optical imaging: Temporally encoded maps of intrinsic signal. Neuron. 2003 May 22;38(4):529-45 .

Taha, S. and Stryker, M.P. Rapid ocular dominance plasticity requires cortical but not geniculate protein synthesis. Neuron. 2002 Apr 25;34(3):425-36.