The Effect Of Glucocorticoid Receptor Function On The Behavior Of ADHD Rats And The Mechanism Of Interaction Between It And MAO A

Objective: Comparing the differences in behavior of ADHD animal models,including spontaneously hypertensive rat(SHR),WKY and SD rats.Observing the changes of behavior in SHR before and after using glucocorticoid receptor(GR)agonist dexamethasone(DEX)or GR inhibitor mifepristone(RU486)and researching the function of GR on the expression of Sp1 and MAO A in different brain regions of newborn SD rats,then to explore the relationships between Sp1 and MAO A to reveal the interaction between GR function and MAO A and the potential mechanism of ADHD.Method:(1)Behavioural evaluation:(1)Animal grouping: As the ADHD model,male SHR on 21 postnatal day(P21)were divided randomly into 3 groups: GR agonist group(SHR+DEX group),GR inhibitor group(SHR+RU486 group)and SHR control group(SHR group),8 rats in each group.8 P21 WKY male rats and SD male rats were used as the WKY group and the SD group respectively.(2)Drug administration: The rats in SHR+DEX group and SHR+RU486 group were given Dexamethasone(0.5 mg/kg·d)or Mifepristone(54 mg/kg·d)separately,and rats in SHR group,WKY group and the SD group were administered saline 0.5ml/kg·d respectively by intraperitoneal injection at 8:00 am for 14 days.(3)Behavioral tests: Locomotor activity and non-selective attention of rats were evaluated by using open field test and Lat maze.(2)The expression of Sp1 and MAO A:(1)Grouping and drug intervention: A total of 24 newborn SD pups(0~48h)in either gender were used.The tissues from the frontal cortex and hippocampus of rats were divided into DEX group,RU486 group and control group randomly.After digesting and precipitating the tissues of each group,neurons were purified and cultured for 48 hours.Then the neurons of frontal cortex and hippocampus in DEX group,RU486 group and control group were administered by DEX 100nmol/L,RU486 10umol/L and equal volume solvent respectively.These cells were then cultured for an additional 48 h.(2)The expression of Sp1 and MAO A: Immunocytochemical staining was used to detect the expression of Sp1 and MAO A in different brain regions(prefrontal cortex and hippocampus),and then the cumulative light density was used to reflect Sp1 and MAO A expression levels.Results:(1)The open field test:(1)Before drug intervention,the number of SHR crossing grid(71.63±8.02)and upright(46.88±11.14)were increased significantly than those in WKY rats(6.25±1.4;3.38±1.88)and in SD rats(3.88±1.96;3.50±1.51)(P<0.001).Comparing with WKY rats,the number of crossing grid in SD rats were decreased,while had higher number of grooming(4.13±1.81 vs 15.00±4.87),and there was no obvious differences in the number of upright between them(P>0.05).(2)After DEX administration,the number of crossing grid(54.38±10.42)and grooming(12.38±2.50)in SHR were significantly decreased,but after giving RU486 intervention,there were no statistic differences in that(P>0.05).(2)The Laze maze test:(1)Before drug intervention,the number of crossing the corner and upright in SHR(91.50±18.10;125.50±15.18)showed a marked increase comparing with that in WKY rats(39.75±10.43;38.00±9.84)and in SD rats(46.38±5.26;15.00±4.07).The number of leaning in SHR(37.38±10.10),compared with WKY rats(29.00±9.96),was no significant difference(P>0.05).Comparing with SD rats,the number of upright and leaning(11.75±3.28)in WKY rats were increased.(2)After giving DEX intervention,the number of crossing the corner(59.88±9.09)and upright(52.13±15.33)in SHR were significantly decreased.After RU486 treatment,the number of crossing the corner was not affected(P>0.05),while upright times(115.75±24.35)were increased.Comparing with SD rats(18.75±8.90;15.25±7.46),the number of upright(31.13±4.42),as well as leaning times(27.75±5.65)in WKY rats were risen.(3)Expressions of Sp1 and MAO A: Comparing with the control group,the expressions of Sp1 and MAO A in the hippocampus(55593.89±3048.37;51232.18±1242.51)in the DEX group(74816.16±2327.20;65643.31±3881.68)were distinctly increased(P<0.001),while in the RU486 group(44751.96±2982.23;45873.93±3726.63)were decreased(P<0.001).The expressions level of Sp1 and MAO A in the prefrontal cortex(84966.93±3017.35;74601.66±3346.72)were higher in DEX group than in control group(P<0.001),but the expressions of Sp1 and MAO A of RU486 group(56166.81±1625.73;36218.07±2912.10)were obviously lower than that of control group(P<0.05).(4)The correlation analysis showed the positive correlation of the expression of Sp1 and MAO A both in the hippocampus neurons and the prefrontal cortex neurons(r=0.947,P<0.001;r=0.965,P<0.001).Conclusion: SHR can be as a feasible and reliable animal model of ADHD combined subtype.However,whether WKY rats can be as an ideal animal model of ADHD attention deficit subtype or not,which remain to be studied.GC can improve the spontaneous activity and non-selective attention of SHR effectively,which indicates that ADHD has abnormal function in HPA axis.GC can enhance the expression of Sp1 and MAO A in the neural cells by activating the GR.Moreover,there is a positive correlation between Sp1 and MAO A.These findings suggest that the interaction mediated by Sp1 between GR function and MAO A may involve in the pathogenesis of ADHD.