The Effects Of Antiepileptic Drugs On Epileptic Immature Rats And The Possible Mechanisms

BackgroundEpilepsy is a common chronic disease of nervous system, wiht high incidence childhood involving cognitive impairement. Multiple factors led to this problem, including the seizure type, frequency and duration, etiology, local ization of the epileptic focus, age at onset of epilepsy, antiepi1optic drugs and so on. Anti-epileptic drugs are the most widely used medications for the treatment of epilepsy. However, many clinical and animal experiments have found that traditional anti-epileptic drugs affect cognition in various aspects, including spatial learning and memory, locomot ion, at tention and even emotion. In the recent years, new anti epileptic drugs such as sodium valproate, levetiracet am, lamotrigine topiramate, oxcarbazopine were widely used in pediatric practice. Although solid evidences are scarcely available, the general belief is that newer anti epileptic drugs may have mild effects on cognition than traditional anti-epileptic drugs. To support, this belief, the cognitive influence of newer anti epileptic drugs should be thoroughly studied.To date, the mechanism of the impact of antiepileptic drugs on cognition is not well understood. This has caused confusion amongst clinicians as to how to prevent side effects of anti-epileptic drugs. Previous experiments have shown that anti-epileptic drugs in newborn rodents may cause neurotoxicity, of which the mechanism is believed to the enhancement of neurodegeneration due to increased apoptosis. However, it is not certain whether other common mechanisms also contribute to human neurological deficits caused by perinatal exposure to anti-epileptic drugs, these mechanisms including impairment of proliferation or migration of neuronal progenitors and disturbance of synaptogenesis. Thus, the present study investigated the effects of anti-epileptic drugs on neurotrophins, neurogenesis, mossy fiber sprouting and synaptic plasticity, in an attempt to elucidate the possible mechanisms of anti-epileptic drugs associated cognitive impairment.Currently, rat models usually experience a single status epilepticus. However, children with the clinical condition often have recurring seizures. Several studies have also shown that in immature animals, a single long seizure rarely results in cell loss and germination, and has little effect on learning, memory and behavior. Therefore, in the experiments presented here, we have used neonatal rats that have experienced three pilocarpine-induced seizures as a model to observe the effect of long-term application of anti-epileptic drugs on cognition in the developing brain.in addition, since the neonatal brain is immature due to underdeveloped synaptogenesis, immature brain is different from the mature one both in physiology and anatomy, immature brain is easier to occur seizure. On the other hand, children with epilepsy often receive anti-epileptic drugs for longer time, effets of anti-epileptic drugs on immature brain may be different from the mature one. Therefore it is necessary to explore the effects and mechanism of anti-epileptic drugs on cognition to pave the way for safe and efficacious clinical practice for neonate and infants.ObjectivesThe aim of is to elucidate the effects and mechanisms of long term anti-epileptic drugs treatment on immature brain cognition. From the aspects of spatial learning and working memory, locomotor activity, neurotrophins expression, neurogenesis, mossy fiber sprouting, synaptic plasticityMethods1. The male Wistar rats (P1) were randomly divided into two groups, group epilepy and group control. Rats in group epilepsy were given intraperitoneal injections of pilocarpine on P1, P4and P7after birth. Rats in Group control were injected with the same volume of saline in the same way. In epilepy group, all surviving rats were randomly divided into six groups on P8:EP+NS, EP+LEV, EP+VPA, EP+OXC, EP+TPM, EP+LTG. In control group, rats were also randomly divided into six groups:CON+NS, CON+LEV, CON+VPA, CON+OXC, CON+TPM, CON+LTG. From the P8, rats in the drug treatment group were administered VPA, LEV, TPM, OXC, LTG respectively; the remaining rats were treated with saline.2. After3-weeks treatment with anti-epileptic drugs, locomotor activity were checked by using open field tests on P29, spatial learning ware checked by using Morris water maze on P31and working memory were checked by using Y maze on P37.3. After above tost, all rats in the epilepsy groups and the controls were sacrificed and randomly subgouped for, western blot and real time PCR detection, BrdU staining or Timm’s staining, respectively.Results1. VPA treated rats gain weight and LTG treated rats lost weight compared with the control rats (P<0.05). In open field test EP+NS group has lower locomotor activity than CON+NS group (P<0.05); LEV treatment promoted rat locomotor activity while LTG treatment suppress rats activity. Inmorris water maze, rats in EP+NS group, VPA group and CON+TPM group need longer time to find the platform but shorter time in the target quadrant than CON+NS group (P<0.05). Rats in EP+LEV group need shorter time to find the platform and longer time in the target quadrant.(P<0.05); Rats in OXC group, LTG group, EP+TPM group and CON+LEV group had no differences with corresponding control group in the test (P>0.05); In Y maze test, all control rats(except CON+TPM group)and EP+LEV group rats have a good grasp of the left-right alternative memory model. rats in CON+TPM group and all epileptic rats(except EP+LEV group) are difficult in working memory, total errors of the initial ten trials were similar to the latter ten trials for these rats.2. The brain weight of EP+NS group rats was lower than CON+NS group (P<0.05), Long-term treatment with VPA and TPM reduced brain weight while LEV increased the brain weight of EP+LEV group rats(P<0.05);VPA and TPM suppressed the expression of BDNF in the developing brain, LEV and LTG increased the expression of BDNF (P<0.05);Compared with those in the control+NS group, rats in the EP+NS group showed an increased number of BrdU-labeled cells in the dentate gyrus, hilus, CA3region and outer area of the hippocampus (P<0.01).Neurogenesis increased in the rats treated with VPA but reduced in the rats treated with LEV, TPM, OXC, LTG; EP+NS group had significantly more Timm particles than CON+NS group In the hippocampal CA3area and supragranular layer (P<0.05),the effect of anti-epileptic drug on mossy fiber sprouting was not significant(P>0.05); VPA suppressed the expression of SNAP-25in the developing brain while other anti-epileptic drugs in this study have no effect on it.Conclusions1. Anti-epileptic drugs exhibit different effects on cognition.(1) VPA cause damage to the spatial learning and memory ability but have no adverse effect on working memory and locomotor activity.(2)LEV improve the spatial learning and memory ability, working memory of epileptic rats but have no positive effects on normal rats, LEV increase locomotor activity.(3)TPM impair spatial learning and working memory of normal rats but have no adverse effect on epileptic rats. TPM have on effect on locomotor activity.(4)LTG have no adverse effect on spatial learning and working memory but depress locomotor activity.(5) Oxc have no adverse effect on spatial learning and memory ability, working memory and locomotor activity.2. Different anti-epileptic drugs affect cognition through different mechanisms(1) VPA cause reduction in brain weight, suppresse the expression of BDNF and SNAP-25in brain, increase neurogenesis, but have no effect on mossy fiber sprouting in young rats, with or without epilepsy(2)LHV increase the expression of BDNF and the brain weight of epileptic rats, reduce HP-induced neurogenesis, but have no effect on the expression of SNAP-25, mossy fiber sprouting and the brain weight, of normal rats.(3)TPM cause reduction in brain weight, suppresse the expression of BDNF in brain, reduce EP-induced neurogenesis, but have no effect on the expression of SNAP-25and mossy fiber sprouting(4) LTG increase the expression of BDNF and the brain weight of epileptic rats, reduce EP-induced neurogenesis, but have no effect on the expression of SNAP-25, mossy fiber sprouting and the brain weight.(5) OXC reduce EP-induced neurogenesis, have no effect on the expression of BDNF and SNAP-25, mossy fiber sprouting and the brain weight.