Studies of physiology and the morphology of the cat LGN following proton irradiation

Purpose: We have examined the effects of proton irradiation on the histolog ic and receptive field properties of thalamic relay cells in the cat visual system. The cat lateral geniculate nucleus (LGN) is a large structure with well-defined anatomical boundaries, and well-described afferent, efferent, and receptive field properties. Methods and Materials: A 1.0-mm proton microbeam was used on the cat LGN to determine short-term (3 months) and long-term (9 months) receptive field e ffects of irradiation on LGN relay cells. The doses used were 16-, 40-, and 60-gray (Gy), Results: Following irradiation, abnormalities in receptive field organizati on were found in 40- and 60-Gy short-term animals, and in all of the long-t erm animals. The abnormalities included "silent" areas of the LGN where a v isual response could not be evoked and other regions that had unusually lar ge or small compound receptive fields, Histologic analysis failed to identi fy cellular necrosis or vascular damage in the irradiated LGN, but revealed a disruption in retinal afferents to areas of the LGN, Conclusions: These results indicate that microbeam proton irradiation can d isrupt cellular function in the absence of obvious cellular necrosis, Moreo ver, the area and extent of this disruption increased with time, having lar ger affect with longer post-irradiation periods. (C) 2000 Elsevier Science Inc.