Quantitative Analysis of Effects of a Single 60Co Gamma Ray Point Exposure on Time-Dependent Change in Locomotor Activity in Rats

Keiko Otani,Hitoshi Sato,Tolebay Rakhypbekov,Noriyuki Kawano,Masaharu Hoshi,Nailya Chaizhunusova,Megu Ohtaki,Nariaki Fujimoto,Aisulu Saimova

doi:10.3390/ijerph17165638

Abstract

Investigating initial behavioral changes caused by irradiation of animals might provide important information to aid understanding of early health effects of radiation exposure and clinical features of radiation injury. Although previous studies in rodents suggested that radiation exposure leads to reduced activity, detailed properties of the effects were unrevealed due to a lack of proper statistical analysis, which is needed to better elucidate details of changes in locomotor activity. Ten-week-old male Wistar rats were subjected to single point external whole-body irradiation with 60Co gamma rays at 0, 2.0, 3.5, and 5.0 Gy (four rats per group). Infrared sensors were used to continuously record the locomotor activity of each rat. The cumulative number of movements during the night was defined as “activity” for each day. A non-linear mixed effects model accounting for individual differences and daily fluctuation of activity was applied to analyze the rats’ longitudinal locomotor data. Our statistical method revealed characteristics of the changes in locomotor activity after radiation exposure, showing that (1) reduction in activity occurred immediately—and in a dose-dependent manner—after irradiation and (2) recovery to pre-irradiation levels required almost one week, with the same recovery rate in each dose group.

Highlights

In humans, one of the earliest effects of radiation exposure to the whole body or to a large portion of the whole body is a prodromal period of nonspecific signs and symptoms such as nausea, emesis, fatigue, fever, and anorexia [1,2]
Regression analysis was first performed with all parameters of the non-linear mixed effects model (NLMM), model selection was applied by choosing the smallest AIC to determine the optimal NLMM
Estimates of fixed-effect parameters and their 95% confidence intervals under the full and optimal NLMM are shown in Tables 1a and 1b respectively; those under the full and optimal non-linear regression model (NLRM) are shown in Tables 2a and 2b, respectively

Summary

Introduction

One of the earliest effects of radiation exposure to the whole body or to a large portion of the whole body is a prodromal period of nonspecific signs and symptoms such as nausea, emesis, fatigue, fever, and anorexia [1,2]. The prodromal syndrome is generally mild or absent at total body doses of 1 Gy or less and occurs from minutes to days following exposure [3,4,5]. It is unclear to what extent these symptoms are psychogenic versus radiation-induced. The relationship between initial symptoms and radiation dose is not well understood. Res. Public Health 2020, 17, 5638; doi:10.3390/ijerph17165638 www.mdpi.com/journal/ijerph

Objectives

Methods

Results

Conclusion