Diurnal Variation in Trigeminal Pain Sensitivity in Mice

Management of time and circadian disruption is an extremely important factor in basic research on pain and analgesia. Although pain is known to vary throughout the day, the mechanism underlying this circadian variation remains largely unknown. In this study, we hypothesized that the process of pain transmission to the central nervous system (after receiving nociceptive stimuli from outside the body) would show day-night differences. Ten-week-old male mice were kept under a strict 12/12-h light/dark cycle for at least 10 days. Formalin was then injected into the second branch region of the trigeminal nerve and the duration of pain-related behaviors (PRBs) was assessed. Immunohistochemical staining was then performed, and the c-Fos-immunopositive cells in the trigeminal spinal tract subnucleus caudalis (Sp5C) were counted. The results showed that the duration of PRBs was longer and the number of c-Fos immunopositive cells in the Sp5C was higher at nighttime than during the day. In addition, the trigeminal ganglia (TG) were extracted from the mice and examined by quantitative real-time PCR to evaluate the daytime and nighttime expression of nociceptive receptors. The results showed that the mRNA expression of transient receptor potential ankyrin 1 in the TG was significantly higher at night than during the day. These results suggest that pain in the trigeminal nerve region is more intense at nighttime, when rodents are active, than during the daytime, partly due to differences in nociceptor expression.

[Distribution Characteristics and Source Analysis of Water-soluble Ions in Particulate Matter Under Different Weather Processes in Nanjing]

From November 16 to 28 2018, water-soluble ions in particulate matter and some trace gases in Nanjing City were observed using the online gas composition and aerosol monitoring system MARGA ADI 2080. Combined with meteorological elements and sounding data, the distribution characteristics and day-night differences of pollutants and water-soluble ions during haze, fog, clear, and precipitation processes were analyzed. The results show that the average concentration of PM_2.5 varied from 26.9μg·m^-3 (precipitation) to 96.4μg·m^-3 (haze) while total water-soluble ions varied between 23.7μg·m^-3 (precipitation) and 89.7μg·m^-3 (haze). The ranked order of ion concentrations was NO₃^- > NH₄⁺ > SO₄^2- > Cl^- > K⁺ > Ca²⁺ > Na⁺ > Mg²⁺ during haze and fog events, and NO₃^- > SO₄^2- > NH₄⁺ > Cl^- > Ca²⁺ > K⁺ > Na⁺ > Mg²⁺ during clear weather and precipitation period. The diurnal distributions of water-soluble ions were quite different under the four conditions, although SO₄^2-, NO₃^-, and NH₄⁺(SNA) were ranked haze > fog > clear > precipitation for both day and night periods. According to the PMF source analysis, secondary sources were the main factors affecting haze; secondary sources, sea salt, and combustion sources were the main pollution sources to foggy conditions; and the removal effect of precipitation on coal-fired sources and secondary sources was more notable than during clear conditions.

[Analysis of Pollution Characteristics and Sources of PM2.5 Chemical Components in Chengdu in Winter]

Day-night PM_2.5 samples were continuously collected in Chengdu from January 1 to 20, 2017, and the concentrations of major chemical components (water-soluble ions and carbonaceous components) were measured in the laboratory. During the observation period, the average mass concentration of PM_2.5 was (127.1±59.9) μg·m^-3. The mass concentration of water-soluble ions was (56.5±25.7) μg·m^-3 and SO₄^2-, NO₃^-, and NH₄⁺ were the most dominant ions with a concentration of (13.6±5.5), (21.4±12.0), and (13.3±5.7) μg·m^-3, respectively, accounting for 85.6% of the water-soluble ions. The average mass concentrations of organic carbon (OC) and elemental carbon (EC) were 34.0 and 6.1 μg·m^-3, respectively, accounting for 26.8% and 4.8% of the PM_2.5 mass concentration, respectively. The comparison of the average day-night concentration shows that the daytime and nighttime mass concentrations of PM_2.5 are (120.4±56.4) and (133.8±64.0) μg·m^-3, respectively, and that the nighttime pollution is more serious. The SO₄^2-, NO₃^-, and NH₄⁺ concentrations are higher during the day than at night, which is related to daytime light, which promotes the formation of secondary ions. The Cl^-, K⁺, OC, and EC concentrations increase significantly, which may be affected by increased emissions from coal and material combustion. Based on the literature review and comparison of the winter chemical composition of PM_2.5 in Chengdu in recent years, the SO₄^2- concentration significantly decreases from 50.6 μg·m^-3 in 2010 to 13.6 μg·m^-3 in 2017. The NO₃^- concentration changes little; it is maintained at~20 μg·m^-3. The analysis of the acid-alkali ion balance shows that PM_2.5 in Chengdu is alkaline due to the relative overgrowth of NH₄⁺, which is different from previous partially acidic results. The average value of NO₃^-/SO₄^2- is 1.57. Mobile sources have a greater impact on the PM_2.5 pollution in Chengdu in winter. The correlation coefficients of OC and EC between daytime and nighttime are 0.82 and 0.90, respectively (P<0.01), which indicates that the OC and EC sources are consistent. The SOC estimation shows that the SOC concentrations during the day and night are 8.5 μg·m^-3 and 11.9 μg·m^-3, respectively, accounting for 28.1% and 30.8% of the OC, respectively. The K⁺/EC average value is 0.31 and the correlation coefficient between K⁺ and OC is 0.87 (P<0.01), indicating that biomass combustion has a certain influence on the carbonaceous aerosol in Chengdu in winter. The principal component analysis shows that the winter PM_2.5 in Chengdu mainly originates from combustion sources (coal burning, biomass burning, etc.), secondary inorganic sources, and soil and dust sources. The contribution rates are 32.8%, 34.5%, and 21.5%, respectively.