Effect On Anxiety, Learning And Memory Of Receptor Induced By Combined Traffic Noise From Freeway And High-speed Railway

In order to study effects of combined traffic noise on anxiety, learning and memory of the body, freeway noise from Shanghai-Hangzhou-Ningbo freeway and high-speed railway noise from Shanghai-Hangzhou railway were sampled, respectively. Day-night equivalent sound level (Ldn) of the combined traffic noise, which was made of the above two types of noise samples, was adjusted to 70 dBA according to traffic flow of freeway and train schedules of high-speed railway. The combined traffic noise of 70dBA was considered as the experimental sound for 52 days’noise exposure. Institute of Cancer Research (ICR) mice and Sprague Dawley (SD) rats whose central nervous systems are similar to humans’were selected as the experimental subjects. Under noise exposure for different days, as well as after cessation of noise exposure, a series of neurophysiology experiments were conducted for different groups of animals, including neurobehavioral experiments (i.e., open field test, light-dark box test and Morris water maze test), determination of concentrations of monoamine neurotransmitters (i.e., norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT)) in plasma, determination of concentrations of amino acid neurotransmitters (i.e., glutamic acid (Glu) and y-aminobutyric acid (GABA)) in hippocampus, detection of expressions of proteins (i.e., phosphorylated Ca2+/calmodulin-dependent protein kinase II (p-CaMKII) and N-methyl-D-aspartate receptor 1 (NR1)) in dorsal hippocampus, and observation of ultrastructure of nerve tissues in hippocampus regions of CA1 and CA3, temporal lobe and amygdala.Among the above neurophysiology experiments, open-field test (with behavioral indicators of center time, line crossing frequency, rearing frequency, climbing frequency), light-dark box test (with behavioral indicators of time spent in lit compartment, transition number) and determination of concentrations of monoamine neurotransmitters (i.e., NE, DA and 5-HT) are anxiety-related. Results show that there were no significant difference between various neurophysiological indicators of experimental group and control group during the whole experimental period (P>0.05), except that the line crossing frequency on the 34th day and the level of DA on the 12nd day during noise exposure were significantly decreased for the mice in experimental group compared with those of control group (P<0.01). These results indicated that the combined traffic noise of 70 dBA had little influences on emotion and activity of the mice, and the longer the noise exposure was, the smaller the influence became.Learning and memory ability were tested through Morris water maze (with behavioral indicators of escape latency, platform crossing frequency,% time in target quadrant), determination of hippocampus neurotransmitters (i.e., Glu and GABA), detection of expressions of proteins (i.e., p-CaMKII and NR1) in hippocampus, and observation of ultrastructure of nerve tissues (i.e., neuron and synapsis). Results show that the difference of each neurophysiological indicator above between experimental group and control group was not to significant degree (P>0.05) during the whole experimental period; after combined traffic noise exposure for 52 days, there were no obvious apoptosis appeared in neurons of hippocampus regions of CA1 and CA3, temporal lobe cortex and amygdala of the rats, meanwhile, synaptic plasticity in the several brain regions has not changed. The results of above experiments were in accordance with each other and indicated that long-term stimulus of combined traffic noise of 70 dBA (Ldn) would not have obvious influence on learning and memory of the mice and the rats.A comparison was made between the neurophysiological effect of combined traffic noise in this study and that of single traffic noise in previous studies. It was shown that with the same Ldn of 70 dBA, the influence of combined traffic noise on anxiety, learning and memory was lower than that of single high-speed railway noise. The difference may due to the weaker burstiness and the lower LAmax, which is the maximum of A-weightd sound pressure level and could be a critical factor to cause the difference, of combined traffic noise.