Hibernation as a Tool for Radiation Protection in Space Exploration

Abstract

With new and advanced technology, human exploration has reached outside of the Earth's boundaries. There are plans for reaching Mars and the satellites of Jupiter and Saturn, and even to build a permanent base on the Moon. However, human beings have evolved on Earth with levels of gravity and radiation that are very different from those that we have to face in space. These issues seem to pose a significant limitation on exploration. Although there are plausible solutions for problems related to the lack of gravity, it is still unclear how to address the radiation problem. Several solutions have been proposed, such as passive or active shielding or the use of specific drugs that could reduce the effects of radiation. Recently, a method that reproduces a mechanism similar to hibernation or torpor, known as synthetic torpor, has started to become possible. Several studies show that hibernators are resistant to acute high-dose-rate radiation exposure. However, the underlying mechanism of how this occurs remains unclear, and further investigation is needed. Whether synthetic hibernation will also protect from the deleterious effects of chronic low-dose-rate radiation exposure is currently unknown. Hibernators can modulate their neuronal firing, adjust their cardiovascular function, regulate their body temperature, preserve their muscles during prolonged inactivity, regulate their immune system, and most importantly, increase their radioresistance during the inactive period. According to recent studies, synthetic hibernation, just like natural hibernation, could mitigate radiation-induced toxicity. In this review, we see what artificial hibernation is and how it could help the next generation of astronauts in future interplanetary missions.

Keywords: brain function; cardiovascular function; genomic instability; hibernation; immune function; radiation protection; space; torpor.

Figure 1

Synthetic torpor induced by GABA-A agonist muscimol. (A) In an animal exposed to constant darkness at an ambient temperature of 15 °C, repeated injections of muscimol in the rostral ventromedial medulla (RVMM, the black arrows at the top) induced a suspended animation state characterized by a reduced deep brain temperature (Tbrain), heart rate (HR), and electroencephalogram (EEG) voltage, as well as a shift of the EEG power spectrum. No significant changes in arterial pressure (AP) were observed. Infrared images at the bottom show the state of cutaneous vasomotion (B) in the pre-injection period, (C) following the first injection of muscimol in the RVMM, and (D) at end of treatment. This was adapted from [19]. Copyright 2013, Society for Neuroscience.

Figure 2

Distribution and locations of microinjections of GABA-A agonist muscimol in the brainstem. A key area in the central nervous pathways for thermoregulatory cold defense is the rostral ventromedial medulla (RVMM), a region including the raphe pallidus (RPa). (A) The location of every injection site, marked with fast green after each experimental procedure, was schematically plotted on atlas drawings [26] at four rostrocaudal levels of the RVMM. (B,C) Examples of marked sites at two rostrocaudal levels: 7n = nucleus of cranial nerve VII; IO = inferior olive; Py = pyramid; and Rob = raphe obscurus. This was adapted from [19]. Copyright 2013, Society for Neuroscience.

Figure 3

Schematic description of hibernation as a potential tool for radiation protection in space missions.