Abstract
A recognized risk of long-duration space travel arises from the elevated exposure astronauts face from galactic cosmic radiation (GCR), which is composed of a diverse array of energetic particles. There is now abundant evidence that exposures to many different charged particle GCR components within acute time frames are sufficient to induce central nervous system deficits that span from the molecular to the whole animal behavioral scale. Enhanced spacecraft shielding can lessen exposures to charged particle GCR components, but may conversely elevate neutron radiation levels. We previously observed that space-relevant neutron radiation doses, chronically delivered at dose-rates expected during planned human exploratory missions, can disrupt hippocampal neuronal excitability, perturb network long-term potentiation and negatively impact cognitive behavior. We have now determined that acute exposures to similar low doses (18 cGy) of neutron radiation can also lead to suppressed hippocampal synaptic signaling, as well as decreased learning and memory performance in male mice. Our results demonstrate that similar nervous system hazards arise from neutron irradiation regardless of the exposure time course. While not always in an identical manner, neutron irradiation disrupts many of the same central nervous system elements as acute charged particle GCR exposures. The risks arising from neutron irradiation are therefore important to consider when determining the overall hazards astronauts will face from the space radiation environment.
Highlights
As humans undertake long-duration space exploration beyond low Earth orbit, including missions to the Moon and Mars, they will undergo exposures to a variety of high energy particles
To account for the nested data produced when multiple whole cell electrophysiology recordings were performed in the same animal, differences between treatment groups were evaluated by a linear mixed-effect model regression (LMM)
The goal of the current study was to develop a better understanding of the neurological risks associated with low-dose neutron irradiation, in the context of our prior findings [35] that chronic neutron exposures persistently induce both neurobehavioral and electrophysiological defects in mice
Summary
As humans undertake long-duration space exploration beyond low Earth orbit, including missions to the Moon and Mars, they will undergo exposures to a variety of high energy particles. These include galactic cosmic radiation (GCR) exposures that present a potential hazard to astronauts, likely increasing risks of both carcinogenesis and central nervous system disruptions [1,2]. Cognition becomes negatively impacted by less abundant high atomic number, high energy (HZE), fully ionized nuclei GCR components including 16O [12,13,14], 28Si [15,16], 56Fe [17,18,19] and some combined 2–3 ion exposures [8,20,21,22,23]. We have previously demonstrated that low dose irradiation is sufficient to perturb neuronal intrinsic, synaptic and network properties, whether in response to protons [24,25], 4He [9] or some of the most advanced GCR simulation yet with 5 combined ions [26]
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