Micropatterned
Substrates for Controlling Growth and Neurite
Extension of Retinal Neurons
The
question of how the developing nervous system gets “wired up” has long occupied
the minds of neuroscientists. One of the
earliest hypotheses proposed a significant role for chemical signaling,
suggesting that neurites are guided to their targets
by chemical cues. Subsequent research
has confirmed an essential role for chemical guidance, and has only begun to
unravel what are extremely complex and cell type-specific signaling systems
involving numerous kinds of molecules that play a myriad of roles. Some molecules attract, others repel, some
are diffusible, others act through contact, some induce neurite
outgrowth, others induce cell death, and so forth.24
Many
neural engineers seek to develop devices that interface with the nervous system
for extended lengths of time. Examples
include the cochlear implant, retinal-based visual prostheses, cortical-based
prostheses, deep brain stimulators, and spinal cord stimulators. In all these cases a principle challenge is
to devise an optimal interface between the synthetic device and the neurons
with which the device needs to communicate.
Such optimal interfaces will maximize the specificity of connections
(and thereby maximize information transfer), and maximize the efficiency of
signal transfer (and thereby minimize power requirements). Most devices currently under development are
intended to communicate with a neural substrate using electrical signals, often
bidirectionally, via electrodes. But in principle communication can be through
magnetic or chemical means as well.25
In
order to achieve an optimal interface the synthetic device must “wire up” with
the host nervous system. How can this be
accomplished? One approach is to utilize
the nervous system’s natural mechanisms, that is, use chemical cues to coax
neurons to form appropriate and effective connections with targets in the
synthetic device.
In
our laboratory we are interested in interfacing devices with the retina. As such we have been exploring the
possibility of using certain growth and adhesion molecules to promote the
survival of, and neurite outgrowth from, retinal
bipolar cells. In many degenerative
retinal diseases these cells substantially survive following profound
photoreceptor loss, and constitute a potential target for a visual prosthesis.26
Molecules being tested include small peptides (e.g. IKVAV and KDI) from the extracellular matrix protein laminin,27 as well
as growth factors such as FGF-2. The
proposed REU project is an extension of this work, and has the following goals:
1. Use soft lithography
or other method to create micro-patterns of attractive and repulsive adhesion
molecules on glass or silicon.28
2. Use techniques such as
fluorescent microscopy, Fourier Transform Infrared spectroscopy (FTIR), and
amino acid analysis to quantify the composition of the surface substrate.
3. Culture rat retinal
neurons on the prepared surfaces and determine whether neuron (especially
bipolar cell) survival and neurite outgrowth can be
manipulated by the micropatterned surface.
References
24. Zou Y, Engert F, Tao HW (2004) The assembly of neural circuits. Neuron 43:159.
25. Peterman MC, Bloom DM, Lee C, Bent SF, Marmor MF, Blumenkranz MS, Fishman HA (2003) Localized neurotransmitter release for use in a prototype retinal interface. Invest Ophthalmol Vis Sci 44:3144.
26. Hetling JR, Baig-Silva MS (2004) Neural prostheses for vision: designing a functional interface with retinal neurons. Neurol Res 26:21.
27. Saneinejad S, Shoichet MS (1998) Patterned glass surfaces direct cell adhesion and process outgrowth of primary neurons of the central nervous system. J Biomed Mater Res 42:13.
28. Branch DW, Wheeler BC, Brewer GJ,