Applications Of A Laser Microbeam In The Study Of Degeneration, Regeneration, And Guidance Of Primary CNS Axons
Black, Bryan James
MetadataShow full item record
This thesis explores the applications of a near infrared (NIR) laser microbeam as a tool for manipulating primary axons by initiating femtosecond pulsed-laser plasma-mediated ablation (laser axotomy) and optical guidance. Chapter 1 briefly introduces axon morphology, growth, and the principles of axon guidance, as well as an introduction to the unique capabilities/potential provided by laser microbeams in biological research (laser-tissue interactions). Non-linear, multiphoton absorption processes are discussed in context of biological tissue ablation. In addition, we discuss specific challenges facing mammalian central nervous system (CNS) axons subsequent to injury, and comment on strategies which can be employed to mitigate, remove, or circumvent those challenges using neuroprotective factors and NIR laser microbeam.With a basic understanding of laser-tissue interaction, Chapter 2 presents results on degeneration and regeneration dynamics of retinal ganglion cell (RGC) axons subsequent to varying degrees of fs laser-induced injury. Axons were damaged using three distinct sets of parameters, resulting in three reproducibly distinct initial injuries (all resulting in complete axotomy). Regeneration rates and pathfinding abilities were shown to decrease in axons suffering higher degree of initial injury. Chapter 2 also presents results of degeneration and regeneration dynamics subsequent to fs laser axotomy in the presence and absence of estrogen, which has been shown to mitigate degenerative effects and is implicated in successful regeneration of CNS axons.Chapter 3 presents a novel, purely optical method to guide the growth of primary CNS axons that uses a low power, near infrared laser microbeam. This non-contact method is highly efficient in realizing large turning angles and is 100% effective. Optical guidance is successfully applied to primary RGC, as well as rat cortical neuron (RCN) axons. Possible mechanisms of guidance are discussed and analyzed using optical force (photomechanical) and local temperature rise (photothermal) simulations. This method is minimally invasive and is adaptable to fiber-optics, illustrating exciting potential as a method of bypassing CNS glial scar formations, which are major inhibitory factors in CNS nerve repair. Applications of optical guidance to spinal cord injury repair and neural circuitry formation are discussed in detail, as is the future direction of our research (Chapter 4).