Ultrastructural changes in the cerebellum after focal deuteron irradiation. Cerebellar irradiation.

Abstract

Previous studies have indicated only negligible damage to nerve cells of the cerebral and cerebellar cortex after irradiation with microbeams at 5000 rads or more of energy (32). A number of studies have also suggested that higher doses may selectively destroy only certain types of cells (19, 20). Consequently, focal microbeam irradiation techniques with monoenergetic particles may be particularly suitable for examining differential cellular radiosensitivities within a region of the brain containing heterogeneous cell populations. Since the small geometric configuration of such a focal field minimizes vascular and indirect abscopal effects (23, 31, 33), it also seems more likely that specific information on some of the earliest irradiation effects on nerve cell structure and function can be obtained by exposure to high dose microbeam irradiation with subsequent examination of the irradiated tissues by electron microscopy. The present investigation was undertaken with monoenergetic particles to examine in greater detail the earliest sequence of ultrastructural changes observable directly in a beam path produced by focal deuteron irradiation of the cerebellum in adult mice. This particular region of the central nervous system was selected for more detailed examination since previously reported findings indicated a variety of differential cellular radiation effects between granule and Purkinje cells exposed to similar high dose microbeam irradiation (19). The examination of various early sequential ultrastructural changes was facilitated in the present study by comparative observations of damage to nerve cells and associated vascular and glial elements located directly in the beam path as compared to the appearance of adjacent non-irradiated normal cells. The specific aim of this study was to examine in greater detail the sequence of ultrastructural changes in neurons, blood vessels, and glial elements in the beam path from 5 minutes to 10 days after focal irradiation of the brain.