EFFECT OF LONG-TERM GEOMAGNETIC FIELD DEPRIVATION ON BIOELECTRICAL ACTIVITY OF BRAIN OF LABORATORY RATS

The Earth's magnetic field plays an important role in the activity of living organisms by affecting the course of physiological processes taking place in the body and, consequently, in the behaviour. The aim of the study was to estimate the effect of long-term deprivation of geomagnetic field on brain's bioelectrical activity and behaviour of laboratory rats. The geomagnetic field deprivation, which was supported at zero during 21 days, is achieved by compensation of the magnetic field of the Earth by the system of Helmholtz coils. Fluctuations of the Earth's magnetic field were taken into account using a computer program that calculates current strength for the real time compensation solenoids. The object of the study was mature male rats (12 control rats and 12 rats of the experimental group). Their behaviour before and after exposing them to the weakened geomagnetic field was assessed by the open field test (the latent period of exit from a central square, horizontal activity, rearing, dipping, emotion, self-grooming). 6 rats of the experimental group and 6 control group rats showed EEG and evoked potentials before and after the experiment using hypodermic needle electrodes. The stimuli were the frequent standard (1000 Hz) and the rare deviant (500 Hz) tones with a probability of 80 and 20% respectively. We assessed the value of the mismatch negativity component, which was calculated as the difference between evoked potentials to deviant and standard stimuli. Significant changes in the behaviour of rats of both the groups in the open field test were not revealed. A significant effect of the investigated factors on the EEG spectrum was observed. The exposition of rats in the hypogeomagnetic environment caused a decrease in power of the theta, alpha, beta and gamma1 bands compared with the control group. The weakening of the geomagnetic field also causes a reduction of the mismatch negativity component in evoked potentials after the experiment for the experimental group of rats. Mismatch negativity is the correlate of automatic detection of any changes by means of auditory sensory system. The results obtained may indicate violations of the bioelectric activity of rat brain during prolonged exposition in the hypogeomagnetic environment, manifested in the sensory load, when changes in the environment occur, at least, in the auditory sensory system. The work was supported by the Federal Goal-Oriented Program "Scientific and Educational Brainpower of Innovative Russia" for 2009-2013.