Early and long-term alterations in sensorimotor parameters following fractionated gamma irradiation in an experimental setting

Introduction. Epidemiological studies suggest that ionizing radiation increases the risk of developing neurodegenerative diseases long after exposure; however, there is a notable lack of longitudinal studies and experimental research into establishing causal relationships between radiation dose and potential neurodegenerative effects.

Objective. The work investigates early and long-term alterations in sensorimotor parameters characterizing coordination in laboratory animals subjected to a range of doses of fractionated gamma irradiation at a young age.

Materials and methods. Experiments were carried out on mice of both sexes (n = 400) of the C57Bl/6 strain. Five observation groups were formed: two control groups and three groups with different radiation exposure levels, each made up of 80 individuals (40 males and 40 females). The animals underwent total external gamma irradiation during their first month of life at cumulative doses of 0.1 Gy, 1 Gy, and 5 Gy, with each dose divided into 20 fractions. The control groups of non-irradiated mice included: a group of intact animals serving as biological control (n = 80) and a sham-irradiation placebo group (n = 80). Evaluation of motor function is an effective tool for assessing symptoms of neurodegenerative diseases in animals. Coordination in irradiated and control animals was assessed using the tapered beam walking test at the ages of 1, 6, 12, and 18 months. Data were analyzed using Microsoft Excel and the R programming language.

Results. Sex and age were shown to influence sensorimotor parameters characterizing motor coordination (better in females, worsens with age in animals of both sexes), while no significant effect of the stress factor associated with animal irradiation was found on the studied parameters. A comparison of sex- and age-standardized sensorimotor parameters between irradiated animals and non-irradiated control mice revealed dose-dependent alterations. A deteriorated in motor coordination in the long term in mice exposed to gamma irradiation at a cumulative dose of 5 Gy manifested itself by a more than 1.5-fold increase in the number of errors compared to non-irradiated animals (t = 6.7; p << 0.001). Conversely, irradiation at a cumulative dose of 0.1 Gy produced an opposite effect: both in the early and long-term periods, the speed of mouse movement along the tapered beam increased relative to the non-irradiated control (walking time decreased by an average of 20% (p < 0.001) at any age), while in the early period, the number of errors also decreased (t = 2.36; p = 0.02), indicating an improvement in coordination ability.

Conclusions. Fractionated gamma irradiation at a young age induced dose-dependent alterations in sensorimotor function in animals: irradiation at a cumulative dose of 0.1 Gy resulted in improved coordination both in the early and long-term periods post-exposure; whereas irradiation at a cumulative dose of 5 Gy led to signs of impaired motor coordination in the long term, at 18 months of age.

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