Exposure to galactic cosmic radiation (GCR) is considered to be a potential health risk in long-term space travel, and it represents a significant risk to the central nervous system (CNS). The most harmful component of GCR is the HZE [high-mass, highly charged (Z), high-energy] particles, e.g. (56)Fe. In ground-based experiments, exposure to HZE-particle radiation induces pronounced deficits in hippocampus-dependent learning and memory in rodents. The mechanisms underlying these impairments are mostly unknown, but some studies suggest that HZE-particle exposure perturbs the regulation of long-term potentiation (LTP) at the CA1 synapse in the hippocampus. In this study, we irradiated rats with 60 cGy of 1 GeV (56)Fe-particle radiation and established its impact on hippocampal glutamatergic neurotransmissions at 3 and 6 months after exposure. Exposure to 60 cGy (56)Fe-particle radiation significantly (P < 0.05) reduced hyperosmotic sucrose evoked [(3)H]-glutamate release from hippocampal synaptosomes, a measure of the readily releasable vesicular pool (RRP). This HZE-particle-induced reduction in the glutamatergic RRP persisted for at least 6 months after exposure. At 90 days postirradiation, there was a significant reduction in the expression of the NR1, NR2A and NR2B subunits of the glutamatergic NMDA receptor. The level of the NR2A protein remained suppressed at 180 days postirradiation, but the level of NR2B and NR1 proteins returned to or exceeded normal levels, respectively. Overall, this study shows that hippocampal glutamatergic transmission is sensitive to relative low doses of (56)Fe particles. Whether the observed HZE-particle-induced change in glutamate transmission, which plays a critical role in learning and memory, is the cause of HZE-particle-induced neurocognitive impairment requires further investigation.
" 2010 ; Cherry et al . , 2012 ; Shukitt - Hale et al . , 2013 ) . A relatively low dose at 50 cGy was shown to induce hippo - campal neurogenesis and neuroinflammation in mice ( Rola et al . , 2008 ) ; a low dose at 60 cGy was found to lead to a persistent reduction in the glutamatergic readily releasable pool of hippocampal synaptosomes in rats ( Machida et al . , 2010 ) , and an even lower dose at 20 cGy was reported to cause a persistent reduction in spatial learning ability in rats ( Britten et al . , 2012 ) . Probably as a result of the higher LET of Fe particles , the survival prob - ability of the cells hit by the Fe particles would be fairly small . Thus loss of critical cellular components in "
"Studies have demonstrated radiationinduced changes in hippocampal cellular activity (Gangloff and Haley, 1960; Bassant and Court, 1978), synaptic efficiency/spike generation (Bassant and Court, 1978; Pellmar and Lepinski, 1993), and neuronal gene expression (Noel et al., 1998; Rosi et al., 2008). For example, irradiating the rodent brain with single and fractionated doses produces changes in (i) neuronal receptor expression of the immediate-early gene activity-regulated cytoskeleton-associated protein (Arc) (Rosi et al., 2008), (ii) N methyl-D-aspartic acid (NMDA) receptor subunits (Shi et al., 2006; Machida et al., 2010), (iii) glutaminergic transmission (Rohde et al., 1979; Machida et al., 2010), and (iv) hippocampal long-term potentiation (LTP; Snyder et al., 2001; Vlkolinsky et al., 2008); all are important for synaptic plasticity and cognition. "
[Show abstract][Hide abstract] ABSTRACT: Approximately 100,000 primary and metastatic brain tumor patients/year in the US survive long enough (> 6 months) to experience radiation-induced brain injury. Prior to 1970, the human brain was thought to be highly radioresistant; the acute CNS syndrome occurs after single doses > 30 Gy; white matter necrosis occurs at fractionated doses > 60 Gy. Although white matter necrosis is uncommon with modern techniques, functional deficits, including progressive impairments in memory, attention, and executive function have become important, because they have profound effects on quality of life. Preclinical studies have provided valuable insights into the pathogenesis of radiation-induced cognitive impairment. Given its central role in memory and neurogenesis, the majority of these studies have focused on the hippocampus. Irradiating pediatric and young adult rodent brains leads to several hippocampal changes including neuroinflammation and a marked reduction in neurogenesis. These data have been interpreted to suggest that shielding the hippocampus will prevent clinical radiation-induced cognitive impairment. However, this interpretation may be overly simplistic. Studies using older rodents, that more closely match the adult human brain tumor population, indicate that, unlike pediatric and young adult rats, older rats fail to show a radiation-induced decrease in neurogenesis or a loss of mature neurons. Nevertheless, older rats still exhibit cognitive impairment. This occurs in the absence of demyelination and/or white matter necrosis similar to what is observed clinically, suggesting that more subtle molecular, cellular and/or microanatomic modifications are involved in this radiation-induced brain injury. Given that radiation-induced cognitive impairment likely reflects damage to both hippocampal- and non-hippocampal-dependent domains, there is a critical need to investigate the microanatomic and functional effects of radiation in various brain regions as we
Frontiers in Oncology 07/2012; 2(July):73. DOI:10.3389/fonc.2012.00073
[Show abstract][Hide abstract] ABSTRACT: To assess whether the effects of cranial (56)Fe irradiation on the spatial memory of mice in the water maze are sex and apolipoprotein E (apoE) isoform dependent and whether radiation-induced changes in spatial memory are associated with changes in the dendritic marker microtubule-associated protein 2 (MAP-2) and the presynaptic marker synaptophysin.
Two-month-old male and female mice expressing human apoE3 or apoE4 received either a 3-Gy dose of cranial (56)Fe irradiation (600 MeV/amu) or sham irradiation. Mice were tested in a water maze task 13 months later to assess effects of irradiation on spatial memory retention. After behavioral testing, the brain tissues of these mice were analyzed for synaptophysin and MAP-2 immunoreactivity.
After irradiation, spatial memory retention of apoE3 female, but not male, mice was impaired. A general genotype deficit in spatial memory was observed in sham-irradiated apoE4 mice. Strikingly, irradiation prevented this genotype deficit in apoE4 male mice. A similar but nonsignificant trend was observed in apoE4 female mice. Although there was no change in MAP-2 immunoreactivity after irradiation, synaptophysin immunoreactivity was increased in irradiated female mice, independent of genotype.
The effects of (56)Fe irradiation on the spatial memory retention of mice are critically influenced by sex, and the direction of these effects is influenced by apoE isoform. Although in female mice synaptophysin immunoreactivity provides a sensitive marker for effects of irradiation, it cannot explain the apoE genotype-dependent effects of irradiation on the spatial memory retention of the mice.
International journal of radiation oncology, biology, physics 06/2011; 80(2):567-73. DOI:10.1016/j.ijrobp.2010.12.034 · 4.26 Impact Factor
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