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.
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,