![]() In the current review we are concerned with the immediate sensory effects of X-rays rather than longer term biological effects of X-rays such as dermatitis, radiation sickness, or mutagenesis. The objective of this review paper is to provide an overview of the many studies conducted to examine sensory effects or perception of X-rays by animals. Presently, a linear dose dependent harmful effect model is generally accepted though other models such as hormesis (i.e., low doses of ionizing radiation are beneficial) have good experimental support but limited acceptance (Baldwin and Grantham, 2015). Investigations of the dose dependence of biological effects of X-rays is in some ways still not nuanced (Widder, 2014). As awareness of these harmful effects has increased, research on the perceptual effects of X-rays has become rare. As a result, much literature on X-ray perception derives from the earliest days of X-ray research when there was little awareness of their harmful effects. In current medical practice, X-ray dose is controlled and generally minimized to mitigate harmful effects while maintaining diagnostic utility (Tafti and Maani, 2022). Thus, X-rays could have significant modulatory effects on ROS-mediated signaling cascades and cellular function and these effects could vary dramatically with the dose delivered. At high concentrations ROS can damage a wide array of cellular components including DNA making ROS mutagenic at higher levels. Importantly, at low concentrations ROS can act as a cellular signal and ROS plays a vital role in signal transduction, metabolic regulation, and homeostatic regulation in processes like apoptosis, autophagy, the cell cycle, and immunity (Moloney and Cotter, 2018 Unable to find information for 178238 Holmström and Finkel, 2014). This leads to a rapid cascade of events and the generation of reactive oxygen species (ROS) which have a wide range of reactivities. Essentially, a high energy photon can kick an electron out of a water molecule and into solution. This is principally due to the ubiquity of water in biological systems. X-rays' impact on biology is principally by radiolysis of water. Abundant elements in tissue (i.e., carbon, hydrogen, oxygen, and nitrogen) have k-edges that are so low they are difficult to detect. These are known as k-edges and this property has led to the use of iodine and barium as clinical contrast agents. For higher Z materials (e.g., iodine, Z = 53), sharp increases in attenuation can be seen at energies near the binding energy of the inner shell electrons. This property has led to the wide use of X-rays for clinical imaging. As a result, X-rays are less attenuated by soft tissues and more attenuated by hard tissues and so X-rays can be used to produce the projections of tissue density known as radiographs. At kilovolt energies (typical clinical values) the attenuation of X-rays per unit mass is approximately proportional to Z 3/ E 3, where Z is the atomic number and E is the energy of the incident photon. X-rays are a form of high energy electromagnetic radiation that can penetrate matter more readily than visible light. The reaction to Röntgen's initial discovery was sensational and led to a veritable explosion of research on the mysterious rays and as early as 1897 when Freund had begun investigations into their biological effects (Widder, 2014). ![]() ![]() X-rays have inspired fascination and curiosity since their discovery in 1895 by Wilhelm Conrad Röntgen and the effects of X-rays on animals and humans have been the focus of many investigations. ![]() Furthermore, we postulate the role of reactive oxygen species (ROS), the most biologically active byproduct of X-rays, as a key mediator of sensory receptor responses to X-rays. Taken together, the reviewed literature provides a large body of evidence that X-rays can induce sensory responses in a wide variety of animals and also suggests that these responses are mediated by known sensory receptors. We focus on the changes in appetitive and consummatory behavior, radiotaxis, behavioral arousal, and olfactory responses to X-rays that have been reported in the literature. ![]() Here we review literature on animal behavioral responses to X-rays from 1895 until 2021 to assess the evidence for detection of X-rays by sensory receptors in animals. These studies examined a range of acute and chronic effects, and a subset of studies has attempted to determine if X-rays can produce any sensory responses. Since their discovery in 1895, many studies have been conducted to understand the effect of X-rays on neural function and behavior in animals. ![]()
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