| Objective:To study the effect of maternal deprivation and chronic unpredictable stress on the behaviors and the expression of dopamine receptors gene, dopamine transporter gene and brain-derived neurotrophic factor gene in the mesolimbocortical dopaminergic neural pathway of rats; To explore whether depressive phenotypes induced by the two stress paradigms differ from each other or not and determine the certain anomaly in the mesolimbocortical dopaminergic neural pathway involved.Methods:Newborn rats were randomly divided into three groups, maternal deprivation group (MD, n=8), chronic unpredictable stress group (CUPS, n=8) and control group (C, n=8). MD rats were exposed to maternal deprivation from postnatal day1to14; CUPS rats were exposed to chronic unpredictable stress for3weeks at the age of10weeks; Control rats received no experimental handle but standard husbandry care. Assessment of rats’depressive behaviors was conducted when they are13weeks old via open field test, forced swimming test and sucrose preference test, four indices including the total distance rats crawled, the rate of central area, vertical activity and the number of fecal pallets were recorded during open field test, the floating time was measured during the forced swimming test and the sucrose and water intake was recorded during sucrose preference test to evaluate the exploratory interest,anxiety level,desperation behavior and anhedonia of rats respectively. All the rats were rapidly decapitated after behavioral tests, and the ventral tegmental area, prefrontal cortex, nucleus accumbens,amygdala, olfactory bulb and striatum were rapidly collected. The protein and mRNA level of dopamine receptors including DRD1/DRD5/DRD2/DRD3/DRD4, dopamine transporter(DAT) and brain-derived neurotrophic factor(BDNF) in the brain regions mention above were detected by Western Blot and Real-Time PCR respectively. One-way analysis of variance (ANOVA) and LSD-test or Kruskal-wallis H and Nemenyi-test and Pearson correlation test was used for analyzing the data collected from the study.Results:1.The result of behavior tests:(1) the result of open field tests:1) total distance rats crawled:no difference in the total distance rats crawled in the open field arena was found between three groups (p>0.05);2) vertical activity:the MD and CUPS rats exhibited no difference in vertical activity, and both of which decreased compared to control rats(p<0.05);3) central area rate:the MD and control rats exhibited no difference in central area rate, and both of which increased compared to CUPS rats(p<0.05);4) the number of fecal pallets:the MD and control rats exhibited no difference in the number of fecal pallets excreted during the open field test, and both of which decreased compared to CUPS rats(p<0.05).(2) the forced swimming test:CUPS rats shown longer floating time in the forced swimming test than MD rats did(P<0.05), the floating time of which were longer than that of the control rats(p<0.05).(3) sucrose preference test:the sucrose preference rate of MD rats was lower than that of CUPS rats(p<0.05), and both of them were lower than the control rats(p<0.05). 2. The result of protein detection:(1) in ventral tegmental area(VTA): compared to control rats, protein level of DRD1, DRD5, DRD2, DRD3, DRD4,DAT and BDNF were downregulated in VTA of MD rats(p<0.05), DRD2was upregulated and DRD5,DRD4were downregulated in VTA of CUPS rats(p<0.05); compared to CUPS rats, protein level of DRD1, DRD5, DRD2, DRD3and BDNF were downregulated in VTA of MD rats(p<0.05).(2) in prefrontal cortex(PFC):compared to control rats, protein level of DRD1, DRD5, DRD3, DRD4and DAT were upregulated and BDNF protein level was downregulated in PFC of MD rats(p<0.05), DRD1, DRD5and DAT were upregulated and DRD2, BDNF were downregulated in PFC of CUPS rats(p<0.05); compared to CUPS rats, DRD3,DRD4were upregulated and DRD5,DAT were downregulated in PFC of MD rats(p<0.05).(3) in nucleus accumbens(NAc):compared to control rats, DRD1, DRD5, DRD2, DRD3, DRD4and DAT protein level were upregulated and BDNF was downregulated in NAc of MD rats(p<0.05), DRD1, DRD5, DRD2, DRD3, DRD4and DAT were upregulated in NAc of CUPS rats (P<0.05);compared to CUPS rats, DAT was upregulated and BDNF was downregulated in NAc of MD rats(p<0.05).(4) in the amygdala(AMy):compared to the control group, DRD1, DRD5, DRD2, DRD3and DRD4protein level were upregulated in AMy of MD rats(p<0.05), DRD5, DRD2, DRD3, DRD4and DAT protein level were upregulated in AMy of CUPS rats(p<0.05); compared to CUPS rats, DRD1was upregulated and DRD4,DAT were downregulated in AMy of MD rats(p<0.05).(5) in the olfactory bulb(OB): compared to control rats, DRD1, DRD5, DRD2, DRD3, DRD4and DAT protein level were upregulated in OB of MD rats(p<0.05), DRD1, DRD2 were upregulated in OB of CUPS rats(p<0.05); No difference in DRD1, DRD5, DRD2, DRD3, DRD4, DAT and BDNF protein level in OB was detected between MD and CUPS rats(p>0.05).(6) the striatum(ST): compared to control rats, DRD5, DRD2, DRD3, DRD4and DAT protein level were upregulated and DRD1was downregulated in ST of MD rats(p<0.05), DRD5, DRD2, DRD3, DAT and BDNF were upregulated and DRDlwas downregulated in ST of CUPS rats(p<0.05); No difference in DRD1, DRD5, DRD2, DRD3, DRD4, DAT and BDNF protein level in ST was detected between MD and CUPS rats(p>0.05).3.The result of mRNA detection:(1) in ventral tegmental area(VTA): compared to control rats, the mRNA level DRD5, DRD2, DRD3, DRD4, DAT and BDNF were downregulated and DRD1was upregulated in VTA of MD rats(p<0.05), DRD2was upregulated and DRD5, DRD4were downregulated in VTA of CUPS rats(p<0.05); compared to CUPS rats, DRD5,DRD2and BDNF mRNA level were downregulated and DRD1was upregulated in VTA of MD rats(p<0.05).(2) in prefrontal cortex(PFC): compared to control rats, DRD1, DRD5, DRD3, DRD4, DAT and BDNF mRNA level were upregulated in PFC of MD rats(p<0.05), DRD1, DRD5, DAT and BDNF were upregulated and DRD2were downregulated in PFC of CUPS rats(p<0.05); compared to CUPS rats, DRD3, DRD4were upregulated and DRD5,DAT were downregulated in PFC of MD rats(p<0.05).(3) in nucleus accumbens(NAc):compared to control rats, DRD1, DRD5, DRD2, DRD3, DRD4, DAT and BDNF mRNA levels were increased in NAc of MD and CUPS rats(p<0.05); compared to CUPS rats, DAT was upregulated and BDNF was downregulated in NAc of MD rats (p<0.05).(4) in amygdala(AMy):compared to control rats, DRD1, DRD5, DRD2, DRD3and DRD4mRNA levels were increased in AMy of MD rats(p<0.05), DRD5, DRD2, DRD3, DRD4and DAT mRNA levels were upregulated in AMy of CUPS rats(p<0.05); compared to CUPS rats, DRD4, DAT mRNA level were downregulated in AMy of MD rats(p<0.05).(5) in olfactory bulb(OB):compared to control rats, DRD1, DRD5, DRD2, DRD3, DRD4and DAT mRNA level were upregulated in OB of MD rats(p<0.05), DRD1, DRD2were upregulated in OB of CUPS rats(p<0.05); No difference in DRD1, DRD5, DRD2, DRD3, DRD4, DAT and BDNF mRNA level in OB was detected between MD and CUPS rats(p>0.05).(6) in striatum(ST): compared to control rats, DRD5, DRD2, DRD3, DRD4and DAT mRNA level were upregulated and DRD1was downregulated in ST of MD rats(p<0.05), DRD5, DRD2, DRD3, DAT and BDNF increased and DRD1decreased in ST of CUPS rats(p<0.05); No difference in DRD1, DRD5, DRD2, DRD3, DRD4, DAT and BDNF mRNA level in ST was detected between MD and CUPS rats(p>0.05).4.The result of correlation analysis between behavioral and the biological indices:(1) the number of vertical activity rats performed in open field test is positively correlated with the DRD5, DRD3, DRD4protein level in ventral tegmental area and DRD1protein level in striatum(p<0.05), and was negatively correlated with DRD2、DRD3、DRD4、DAT protein level in striatum and DRD5、DAT protein level in prefrontal cortex(p<0.05);(2)the floating time rats spent in forced swimming test was positively correlated with DRD2、DRD3、DRD4、DAT protein level in amygdala and DRD1、 DRD5、DAT protein level in prefrontal cortex(p<0.05);(3) the sucrose preference rate of rats was positively correlated with DRD5, DRD3, DAT protein level in ventral tegmental area(p<0.05), and was negatively correlated with DRD2、DRD3、DRD4、DAT protein level in nucleus accumbens and DRD1, DRD5, DRD2, DRD3, DRD4, DAT protein level in olfactory bulb(p<0.05).Conclusion:1. Dissimilar depressive phenotypes in rats might result from the effect of different chronic psychological stressors.2. Different chronic psychological stressors might exert dissimilar effects on the D1-like, D2-like dopamine receptor and DAT gene expression in rats’dopaminergic mesocorticolimbic neural pathway.3. Different depressive-like behaviors might determined by dissimilar abnormality in rats’dopaminergic mesocorticolimbic neural pathway.4. Different chronic psychological stressors might exert dissimilar effects on neural plasticity in rats’ dopaminergic mesocorticolimbic neural pathway. |
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