Abstract

Little is known of the effects of proton irradiation on neural tissue. A 1.0 mm microbeam was used on the cat lateral geniculate nucleus (LGN) to quantify the short term (< 3 months) and long term (< 9 months) effects of radiation damage. The LGN is a large structure with well defined afferent, efferent, and receptive field properties.

Electrophysiological and histological techniques were used to examine the effects of the microbeam at 60, 40, and 16 Gy, administered as a single bolus. Recordings of light evoked responses in the LGN were obtained using microelectrodes in nine animals within 12 weeks of irradiation, and 6 animals within 36 weeks of irradiation. Receptive fields were mapped onto a tangent screen using standard receptive field techniques. Histological measures included afferent termination, myelination, soma/nuclear area, and cell density.

Physiological and histological abnormalities were found in the 60 and 40 Gy, but not in the 16 Gy short term animals. In contrast to controls, areas unresponsive to visual stimuli were found in the irradiated LGN that were surrounded by normally responsive regions. A disruption in the progression of the size of the compound receptive fields in the irradiated LGN was also found. Histological analyses correlated with the physiological data by the absence of afferent termination to regions of the LGN, and having significantly larger soma areas (p < 0.5) on the irradiated vs. control LGN. No necrosis was observed. All effects were isolated to the irradiated LGN. The long term animals exhibited greater degree of disruption at the 60 and 40 Gy levels, and showed disruption at the 16 Gy level, in contrast to the short term animals, suggesting that the mechanism responsible for changing the functional characteristics of the cells without killing them is time and dose-dependent.

The results suggest that the 1.0 mm proton microbeam is capable of disrupting function in the absence of cellular necrosis up to nine months postirradiation. Moreover, this disruption was confined to a single target structure with no observable disruption to surrounding regions.

LLU Discipline

Anatomy

Department

Anatomy

School

Graduate School

First Advisor

Michael A. Kirby

Second Advisor

Paul J. McMillian

Third Advisor

John O. Archambeau

Degree Name

Master of Science (MS)

Degree Level

M.S.

Year Degree Awarded

1994

Date (Title Page)

8-1994

Language

English

Library of Congress/MESH Subject Headings

Protons; Radiation Effects; Spectrometry, X-Ray Emission; Radiotherapy

Type

Thesis

Page Count

x; 108

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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