The Mechanisms By Which SKF-81297 Affect Behaviours In Ananimal Of Attention Deficit Hyperactivity Disorder (ADHD)

BackgroundAttention-Deficit Hyperactivity Disorder (ADHD) is one of the most common chronic neurobehavioural disease encountered in child development. It is characterized by symptoms of developmentally inappropriate inattention, distractibility ,excessive motor activity and impulsivity ofen accompany with behavioural problems and cognitive deficits. It affects 3%-5% of the school-aged population worldwide. The disorder occurs more frequently in males than females, with male-to female ratios ranging from 4:1 to 9:1 on setting. ADHD is most ofen diagnosed during childhood and therefore, over the last decade, it was regarded as a disease which is belong to children. But follw up studies have indicated that 10%-60% of patients continue to suffer from ADHD during late adolescence and adulthood. These children are at risk for developing mood, anxiety, and drug abuse disorder as adult . So ADHD would lead to a series of negative consequences for their academic and personal lives. As a result, more and more attention focus on the ADHD.Although stimulants are the drugs of choice in the treatment of ADHD. Methylphenidate is the first drug for the treatment of ADHD. However, the clinical response to methylphenidate may be absent or insufficient in about 20-30 % drug-treated children while the occurrence of adverse effects with methylphenidate (sleep disturbances, loss of appetite, tics increase...) may sometimes require a dose reduction or even the discontinuation of the treatment. Consequently, there is a need for alternatives to stimulant medication. So it is very important to further explore the mechanism of ADHD for finding a new action point to treatment of ADHD.Many studies don't attempt in the man because many reasons, animal model is a good choice , it can observe, evaluate the symptom of ADHD and specimen may be collected from the brain of animal model to better explore the structure, function, and the change of transmitter under the different state of behaviour or different period of disease. In the animal experiment, we can better control the inheritance and environment factor, thus it is possible to repeated and conformity of response. The etiopathogenisis and influential factor of disease can be reappearance in an animal model, so we can also explore the action in the invasion course of disease. As a result, it is important for an ideal animal model to investigate the etiological factor and pathogenesy of disease.The spontaneously hypertensive rat (SHR) is commonly used as a rodent model of attention deficit hyperactivity disorder(ADHD), as it displays a characteristic pattern of behaviour including increased impulsivity, hyperactivity,and an inability to sustain attention. In addition, D1R densities are elevated in the striatum and nucleus accumbens of SHR which is consistent with the hypothesis that D1R neurotransmission may be altered in ADHD. Hypertension is a confounding factor in the SHR model of ADHD. However, SHR do not develop hypertension until they are adults, from 10 to 12 weeks of age, whereas hyperactivity is observed at 3 to 4 weeks of age before they enter puberty . A series of studies that addressed the criterion validity, constitution validity and predictive validity have been finished. It is suggest that SHR is the best validated animal of ADHD.The aetiology of ADHD is not well understood, but there is converging evidence implicating the catecholamine dysfuction frontal-striatal circuitry . At the genetic level, ADHD is highly heritable and the genetic component as demonstrated by family and twin studies and preliminary evidence supports an association between ADHD and polymorphisms in D1R. Specifically, dysregulation of dopamine (DA) has been hypothesized in ADHD based on the potent efficacy of indirect dopaminergic agonists. In brain, DA effects are mediated through activation of two distinct receptor families, referred to as the D1 and the D2 classes .The DAD1 receptors (D1R), which are expressed highly in the striatum and prefrontal cortex (PFC), may be particularly relevant for ADHD. These receptors are crucial modulators of the motor and cognitive functions mediated by the frontal-striatal circuitry , functions which are impaired in patients with ADHD. So what is the action of D1R in ADHD ,What is the effect of D1R agonists to ADHD and How isit?ObjectiveTo evaluate juvenile spontaneously hypertensive rats (SHR) as an animal model of a developmental disorder, which is diagnosed according to attention deficit/hyperactivity disorder (ADHD). We observe the effects of treatment with a highly selective dopamine D1 receptor agonist SKF-81297 on locomotion and cognition (spatial learning and working memory) of SHR. We also explore the role of D1R in cause of ADHD, by evaluating the effect of SKF-81297 on on D1R expression, IEG and neuron plasticity fator in the PFC of an animal model of ADHD.Methods1. To characterize behavioural alterations, we studied motor activity, as well as attention and cognitive behaviours in juvenile SHR by using open-field environment test, lat maze, morris water maze and Y-maze. All the behavior in the tests were monitored by a CCD video camera and analyzed off-line. 2. The effects of treatment with SKF-81297 on locomotor, spatial learning and memory. Thirty male 4 weeks old SHRs and thirty male 4 week-old WKY rats as the control group were randomly divided into SKF-81297 and saline control groups respectively. There are twenty-four SHRs and WKYs in group of SKF-81297. The SKF-81297 groups were injected i.p. with SKF-81297 (0.5 mg/kg, 5 mg/kg, 10mg/kg) once daily for 14 days. The control groups were treated by saline according to control principle. We evaluate the motor activity by using open-field environment test on the time after 14day administration of SKF-81297. Spatial learning and memory were test by morris water maze from day 9 to 14 during the treatment.3. After 2-weeks treatment with SKF-81297 SHRs and WKYs rats and the controls were divided into two parts. One part was sacrificed by decapitation and the brain was removed on an ice-cold stage. These brains were used in the study of quantitative real-time detection PCR and western blot to observe the effect on immediately early gene(IEG) , dopamine-related receptor(DlR) and protein( calcyon) and neuron plasticity factor (GDNF,arc). The other part that was used in the study of immunohistochemistry.Results1. Ambulatory and rearing activities in the open-field environment were significantly higher in SHR than in their Wistar-Kyoto (WKY) controls;The behavior in a Lat maze during three consecutive 10-min was monitored, frequency of running across the corners and the rearing activities which is useda sa nin dexo fno n-selectivea tention,w eres ignificantlyh igherin SHR than in WKY during either the 30 minutes or the three consecutive 10-min; In the morris water maze test, there are no significant difference of in the time to find the platform between the SHR and WKY groups. In contrast, on the morris water maze there was siginificant difference in the time spend in objective quadrant between 2 groups. In Y maze test, control rats learned the left-right alternative memory model. Total errors in SHRs group significantly increased compared to WKY rats in both training sessions and retention sessions. So the SHRs had deficits in working memoty.2. The effects of SKF-81297 in activity and spatial learing and memory.2.1 The effects of SKF-81297 in activity . After the 14 days the administration of SKF-81297, SHR rats were more behaviourally active than WKY rats after injection with vehicle in all course of test. The 0.5 mg/kg dose of SKF-81297 increased locomotion behaviour and the stereotyped behavior in both SHR and WKY rats and stimulate the rearing in 25-40min. The 5 mg/kg dose increase locomotion behaviour only in 25-40min in SHR and WKY rats, at the same time the stereotyped behavior have a significant increase. The rearing behaviour of SHR rats were raise in the test session,however, the rearing behaviour have been reduced in 5-20min in WKY rats. The 10 mg/kg dose of SKF-81297 produced a biphasic effect on locomotion, which was characterized by an initial decrease followed by later stimulation. The latter stimulatory effect was more pronounced in SHR than in WKY rats when compared to their respective vehicle-injected groups. The rearing behaviour of SHR rats were reduced in 5-20min and 25-40min, however, the rearing behaviour of SHR rats were only reduce in 25-40min.2.2 The effects of SKF-81297 in spatial learing and memory. After the 14 days the administration of SKF-81297, in morris water maze, the SKF-81297 group spent more time in the target quadrant at all dose levels compared with control rats( P<0.05)but the time in finding the platform has no significant difference at all dose levels (P>0.05).3. The effect of SKF-81297 on D1R expression, immediately early gene andneuron plasticity fator in the PFC of SHR/WKY rats.3.1 SKF-81297 increase the expression the c-fos,fosB,and calcyon in the PFC of SHR rats by immunohistochemistry and western-blot.3.2 DIRmRNA and BDNFmRNA in the PFC of SHR/WKY rats were raised by the SKF-81297 dose-dependent in the real-time PCR, no change in expression ofarcmRNA.Conclusion1. Our findings reveal that juvenile SHR manifest behaviours resembling a developmental disorder of ADHD, such as hyperactivity, attention deficit, and disorder of cognition. Using the open-field experiment, Lat maze, morris water maze and Y-maze, we can evaluate the hyperactivity , attention deficit, learing and memory in the animal model of ADHD. It is important to supply the evidence to further study.2. The activity of SHR/WKY rats were effect by different dose of SKF-81297 and the time of test.The SKF-81297 improve the spatial memory of SHR/WKY rats, and have a most significant improvement in the medium dosage . These evidences suggests the activation of the appropriate suitable dopamine receptor is very important to obtain the good cogtion function.3. D1R, BDNF,calcyon and c-fos,fosB have been increased in the different degree by SKF-81297. It is suggest that SKF-81297 is very important to regulate the function of PFC,the course were medicated by D1R, BDNF,calcyon, as a result, the behaviour of SHR/WKY have differently change.