Neuromorphology

Neuromorphology (from Greek νεῦρον, neuron, "nerve"; μορφή, morphé, “form”; -λογία, -logia, “study of”^[1][2]) is the study of nervous system form, shape, and structure. The study of its structure includes looking at the organ system from a physiological and anatomical point of view, as well as on a molecular and cellular level. The field also explores the communications and interactions within and between each specialized section of the nervous system. It is important to note the difference between morphology and morphogenesis, so that the meaning of neuromorphology is not confused. Morphology deals with study of the shape and structure of biological organisms, while morphogenesis studies the biological development of the shape and structure of organisms. Therefore, neuromorphology focuses on the specifics of the structure and not the process by which the structure was developed.

History

Progress in defining the morphology of nerve cells has been slow in its development. It took nearly a century after the acceptance of the cell as the basic unit of life before researchers could agree upon the shape of a neuron. It was originally thought to be an independent globular corpuscle suspended along nerve fibers that looped and coiled.^[3] It was not until the first successful microdissection of a whole nerve cell by Deiters in 1865 that the separate dendrites and axon could be distinguished.^[3] At the end of the 19th century, new techniques, such as Golgi's method, were developed that enabled researchers to view the whole neuron. This Golgi investigation then promoted new research in neuronal spacing by Ramon y Cajal in 1911. Further morphology research continued to develop, including dendritic morphology.

Influence on Neuron Function

Research has supported a relationship between the morphological and functional properties of neurons. For instance, the accordance between the morphology and the functional classes of cat retinal ganglion cells has been studied to show the relationship between neuron shape and function.^[4]

Development

The development of the morphological features of neurons is governed by both intrinsic and extrinsic factors. The neuromorphology of nervous tissue is dependent upon genes and other factors, such as electric fields, ionic waves, and gravity. Developing cells additionally impose geometrical and physical constraints upon each other. These interactions effect the neural shape and synaptogenesis.^[5]

Subfields

General Morphology

Because of the broad range of functions performed by different types of neurons in diverse parts of the nervous system, there is a wide variety in the size, shape, and electrochemical properties of neurons. Neurons can be found in different shapes and sizes and can be classified based upon their morphology. The Italian scientist Camillo Golgi grouped neurons into type I and type II cells. Golgi I neurons have long axons that can move signals over long distances, such as in Purkinje cells, whereas Golgi II neurons generally have shorter axons, such as granule cells or are anoxonic.

Neurons can be morphologically characterizes as unipolar, bipolar, or multipolar. Unipolar and pseudounipolar cells have only one process extending from the cell body. Bipolar cells have a two processes extending from the cell body and multipolar cells have three or more processes extending towards and away from the cell body.

Theoretical Neuromorphology

Main article: Theoretical neuromorphology

Theoretical neuromorphology is a branch of neuromorphology focused on the mathematical description of the shape, structure and connectivity of the nervous system.

Gravitation Neuromorphology

Gravitational neuromorphology studies the effects of altered gravity on the development of the central, peripheral, and autonomic nervous systems. This subfield aims to expand the current understanding of the adaptive capabilities of nervous systems, and specifically examines how environmental effects can alter nervous system structure and function. Environmental manipulations generally include exposing neurons to either hypergravity or microgravity. It is a subset of gravitational biology.

Research Methods and Techniques

A variety of techniques have been used to study neuromorphology, including confocal microscopy, design-based stereology, neuron tracing^[6] and neuron reconstruction. Current innovations and future research include virtual microscopy, automated stereology, cortical mapping, map guided automated neuron tracing and network analysis. Of the currently used techniques for studying neuromorphology, design-based stereology and confocal microscopy are the two most preferred methods. A complete database of neuronal morphology called the NeuroMorpho Database also exists.^[7]

Design-based Stereology

Design-based stereology is one of the most prominent methods for mathematically extrapolating a 3-D from a given 2-D form. It is currently the leading technique in biomedical research for analyzing 3-D structures.^[8]

Confocal Microscopy

Confocal microscopy is the microscopic procedure of choice for examining neuron structures as it produces sharp images with improved resolution and decreased signal-to-noise ratio. The specific way this microscopy works allows one to look at one confocal plane at a time, which is optimal when viewing neuronal structures. Other more conventional forms of microscopy simply do not allow one to visualize all neuronal structures, especially those that are subcellular. Recently, some researchers have actually been combining design-based stereology and confocal microscopy to further their investigations into the specific neuronal cellular structures.

Virtual Microscopy

Virtual microscopy would allow researchers to obtain images with a decreased amount of imaging sessions, thus preserving the integrity of the tissue and decrease the possibility the fluorescent dyes fading during imaging. This method would additionally give researchers abilities to visualize currently unobtainable data, such as rare cell types and the spatial allocation of cells in a specific brain region.^[8] Virtual microscopy would essentially allow for the digitization of all images obtained, therefore preventing deterioration of the data. This digitization could also potentially permit researchers to create a database to share and store their data.

Cortical mapping

Cortical mapping is defined as the process of characterizing specific regions in the brain based on either anatomical or functional features. Current brain atlases are not definitive or homogenous enough to portray specific structural details. Recent advances in functional brain imaging and statistical analysis may however prove to be sufficient in the future. A recent development in this field called the Grey Level Index method allows for more objective identification of cortical regions via algorithms. More sophisticated cortical mapping techniques are still in the process of being developed and this field will most likely see an exponential growth in mapping methods in the near future.

Clinical Applications

Neuromorphology has been used as a new method of exploring the underlying cause of many neurological disorders, and has been included in the clinical study of various neurodegenerative diseases, mental disorders, learning disabilities, and dysfunctions due to brain damage. Neuromophology has been used to study optical nerve damage, specifically looking at lesions and atrophies. Researchers have been using neuromorphological techniques to not only study the damage but also ways to regenerate the damage nerve through ways like axon growth stimulation.

Current and Future Research

Computational Neuromorphology

Computational neuromorophology examines neurons and their substructures by cutting them into slices and studying these different subsections. It also describes the neuromorphological space as a 3-D space. This allows researchers to understand the size of specific neuronal components. Additionally, the 3-D imaging helps researchers comprehend how the neuron transmits information within itself.^[9]

See also

• Cellular Neuroscience
• Morphology (Biology)
• Theoretical Neuromorphology

References

1. ^ Morphology
2. ^ Neuron
3. ^ ^{a b} Peters, Alan; Palay, Sanford L.; Webster, Henry deF. (January 1991). The Fine Structure of the Nervous System: Neurons and Their Supporting Cells. New York: Oxford University Press. ISBN 0-1950-6571-9. 
4. ^ Costa, Luciano Da Fontoura; Campos, Andrea G.; Estrozi, Leandro F.; Rios-Filho, Luiz G.; Bosco, Alejandra (2000). "A Biologically-Motivated Approach to Image Representation and Its Application to Neuromorphology". Lecture Notes in Computer Science 1811: 192–214. 
5. ^ Costa, Luciano da Fontoura; Manoel, Edson Tadeu Monteiro; Faucereau, Fabien; Chelly, Jamel; van Pelt, Jaap; Ramakers, Ger (July 2002), "A shape analysis framework for neuromorphometry", Institute of Physics Publishing 13: 283–310 
6. ^ Oztas, Emin (2003). "Neuronal tracing". Neuroanatomy 2: 2–5. 
7. ^ Costa, Luciano Da Fontoura; Zawadzki, Krissia; Miazaki, Mauro; Viana, Matheus P.; Taraskin, Sergei N. (December 2010). "Unveiling the Neuromorphological Space". Frontiers Computational Neuroscience 4. 
8. ^ ^{a b} Lemmens, Marijke A.M.; Steinbusch, Harry W.M.; Rutten, Bart P.F.; Schmitz, Christoph (2010). "Advanced microscopy techniques for quantitative analysis in neuromorphology and neuropathology research: current status and requirements for the future". Journal of Chemical Neuroanatomy 40 (3): 199–209. 
9. ^ Trinidad, Pablo. "Computational Neuromorphology". University of Texas at Dallas. http://www.utdallas.edu/~trinidad/p2/index.htm. Retrieved 2 November 2011. 

External links

• NeuroMorpho