title: High Dose Gamma Radiation Selectively Reduces GABAA-slow Inhibition.
abstract: Studies on the effects of gamma radiation on brain tissue have produced markedly differing results, ranging from little effect to major pathology, following irradiation. The present study used control-matched animals to compare effects on a well characterized brain region following gamma irradiation. Male Sprague-Dawley rats were exposed to 60 Gy of whole brain gamma radiation and, after 24-hours, 48-hours, and one-week periods, hippocampal brain slices were isolated and measured for anatomical and physiological differences. There were no major changes observed in tissue appearance or evoked synaptic responses at any post-irradiation time point. However, exposure to 60 Gy of irradiation resulted in a small, but statistically significant (14% change; ANOVA p < 0.005; n = 9) reduction in synaptic inhibition seen at 100 ms, indicating a selective depression of the gamma-aminobutyric acid (GABAA)slow form of inhibition. Population spike (PS) amplitudes also transiently declined by ~ 10% (p < 0.005; n = 9) when comparing the 24-hour group to sham group. Effects on PS amplitude recovered to baseline 48 hour and one week later. There were no obvious negative pathological effects; however, a subtle depression in circuit level inhibition was observed and provides evidence for 'radiomodulation' of brain circuits.
authors.affiliation: Anesthesia, Stanford University School of Medicine.
authors.forename: Beza A
authors.initials: BA
authors.lastname: Dagne
authors.affiliation: Anesthesia, Stanford University School of Medicine.
authors.forename: Melis K
authors.initials: MK
authors.lastname: Sunay
authors.affiliation: Anesthesia, Stanford University School of Medicine.
authors.forename: Noëlie S
authors.initials: NS
authors.lastname: Cayla
authors.affiliation: Anesthesia, Stanford University School of Medicine.
authors.forename: Yi-Bing
authors.initials: YB
authors.lastname: Ouyang
authors.affiliation: Department of Radiation Oncology, Stanford University Medical Center.
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Knox
authors.affiliation: Anesthesia, Stanford University School of Medicine.
authors.forename: Rona G
authors.initials: RG
authors.lastname: Giffard
authors.affiliation: Department of Neurosurgery, Stanford University School of Medicine.
authors.forename: John R
authors.initials: JR
authors.lastname: Adler
authors.affiliation: Anesthesia, Stanford University School of Medicine.
authors.forename: Bruce
authors.initials: B
authors.lastname: Maciver
keywords: brain slice; gaba; gamma; inhibition; pain therapy; radiomodulation; synapse; synaptic inhibition