**3. Results**

All data from OFT and HPLC-FLD are expressed as mean ± standard error of the mean (SEM). Differences between means for unpaired samples were tested by one-way analysis of variance (ANOVA) using SPSS Version 16 software. The criterion for significance was *P* < 0.05.

## **3.1. Open field test**

Line crossing number and center area duration were obtained by three individuals working independently, and their mean values were adopted as the final results of OFT.

The line crossing number in OFT is shown in **Figure 1a**, with no significant difference between CG and EG-I over the duration of the experiment. Nevertheless, the line crossing number of EG-II after 8 d of airport noise exposure was significantly less than that of CG (*P* < 0.05). From **Figure 1a**, two conclusions can be drawn: long-term exposure to aircraft noise below *L*WECPN of 75 dB has no significant impact on the line crossing number of rats, while *L*WECPN of aircraft noise reaching 80 dB is likely to have an impact on line crossing number in rats.

The result of center area duration in OFT showed that the center area durations of CG and EG-I in OFT are almost unchanged, but the center area duration of EG-II is significantly longer than that of CG (*P* < 0.05) after the 8 d of noise exposure (**Figure 1b**). On other days, center area duration among the three groups showed no significant difference (*P* > 0.05).

**Figure 1.** Line crossing number (a) and center area duration (b) in OFT.

There were ten rats in each of EG-I and EG-II and five rats in CG. Data are expressed as mean ± SEM. \**P* < 0.05, compared with the CG (ANOVA).

## **3.2. Levels of plasma NE**

Finally, supernatants were filtered with 0.45 μm membrane filters, and high-performance liquid chromatography-fluorimetric detection (HPLC-FLD) was used to measure the concen‐ tration of NE. The instrument parameters used for HPLC-FLD were as follows: column, Agilent Zorbax SB-C18 column (Agilent, US); mobile phase, methanol-buffer (buffer: 0.07 mol NaH2PO4, 10 mmol sodium octanesulfonate, pH 3.5). The gradient procedure of the mobile phase was as follows: at 0 min, 10% methanol and 90% buffer; at 5 min, 10% methanol and 90% buffer; at 30 min, 60% methanol and 40% buffer (1.0 ml/min of flow rate, 20 μl of injection volume, 35.0°C of column temperature, 280 nm of fluorescence excitation wavelength, and 315 nm of emission wavelength). Under these conditions, various substances in plasma were completely separated so that no interference to determination of the targets is experienced.

After being exposed to aircraft noise for 65 d, four rats were randomly selected from the CG and EG-II groups (two per group). We then examined the neuronal and synaptic morphologies of the temporal lobe by transmission electron microscopy (TEM). Rats were anesthetized by administration of an overdose of sodium pentobarbital and then perfused with glutaraldehyde transcardially. The temporal lobe was localized by digital brain stereotaxic instrument (ZH-LanXing B/S, Huaibei, China) with a soft-type cranial drill. After perfusion for about 1 h, we decapitated rats and stripped the whole brain rapidly fixed in glutaraldehyde. After fixed for 24 h, the temporal lobes were removed, cut into thin slices, and further fixed in glutaraldehyde for 3 d. Based on this, slices were washed using PBS, fixed using 1% osmium tetroxide, stained using 2% aqueous solution of uranyl acetate, dehydrated using different concentrations of alcohol and acetone gradient, penetrated and embedded using embedding medium, aggre‐ gated in oven, and finally cut into ultra-thin slices stained using 4% uranyl acetate and citrate. Cell structure in these ultra-thin slices was observed by TEM (Philips Tecnai 10, The Nether‐

All data from OFT and HPLC-FLD are expressed as mean ± standard error of the mean (SEM). Differences between means for unpaired samples were tested by one-way analysis of variance (ANOVA) using SPSS Version 16 software. The criterion for significance was *P* < 0.05.

Line crossing number and center area duration were obtained by three individuals working

The line crossing number in OFT is shown in **Figure 1a**, with no significant difference between CG and EG-I over the duration of the experiment. Nevertheless, the line crossing number of EG-II after 8 d of airport noise exposure was significantly less than that of CG (*P* < 0.05). From **Figure 1a**, two conclusions can be drawn: long-term exposure to aircraft noise below *L*WECPN of 75 dB has no significant impact on the line crossing number of rats, while *L*WECPN of aircraft

independently, and their mean values were adopted as the final results of OFT.

noise reaching 80 dB is likely to have an impact on line crossing number in rats.

lands).

**3. Results**

166 Recent Progress in Some Aircraft Technologies

**3.1. Open field test**

**Figure 2** shows the relationship between the time rats were exposed to different intensities of aircraft noise and the average concentration of plasma NE measured. We found that there was no significant difference in NE levels between EG-I and CG over the period of the noise exposure.

Data are expressed as mean ± SEM. \**P* < 0.05, compared with the CG (ANOVA).

Nevertheless, on the 29th day of noise exposure, the levels of plasma NE between CG and EG-II showed significant difference (*P* < 0.05). By analyzing these results, we found that aircraft noise below *L*WECPN of 75 dB has no significant impact on the plasma NE of rats. Besides, *L*WECPN of aircraft noise reaching 80 dB is likely to have a negative effect on NE levels under long-term exposure. Therefore, we have known that the intensity of aircraft noise and the duration of aircraft noise exposure are the controlling factors to the level of NE in plasma of rats.

**Figure 2.** Relationship between NE concentration and noise exposure duration.

#### **3.3. Temporal lobe cell morphology**

We observed the neuronal and synaptic morphologies of the temporal lobes from TEM and the representative pictures are shown in **Figure 3**. In our experiments, neuronal and synaptic damages were observed in the temporal lobe of EG-II rats, but no damage was seen in the CG.

**Figure 3.** Neuronal and synaptic morphologies of the temporal lobe of rats.

(a) The nuclei (N) in the neurons of the temporal lobe of the CG were oval and their membrane structure was clear, yet mitochondria (M), rough endoplasmic reticula, and other organelles could be seen in cytoplasm, and their distributions were uniform and morphologically normal. (b) The nuclei (N) of neurons in the temporal lobe of EG-II were irregular-shaped, the nuclear membrane was deep-stained and its structure vague, chromatin accumulated along the edge, and cytoplasm was condensed. (c) The synaptic cleft of the temporal lobe area of the CG was clear, and mitochondria and synaptic vesicles.
