Expression Of Orexin MRNA And Positive Cells In The Rat Brain Tissue Of The Epilepsy Model Induced By Kainic Acid

The current anti-epileptic drugs play roles mostly by reducing neuronal ex-citability or increasing the inhibitory neurotransmitter. The occurrence of seizures is considered to be the results of reduction or lack of γ-aminobutyric aci-d (GABA) inhibition in the central nervous system. Orexin, also known as th-e hypocretin, including orexin-A and orexin-B (hypocretin-1and hypocretin-2respectively) derived by proteolytic cleavage from prepro-orexin precursor. A-nd orexin receptor1and2are widely distributed throughout the central ner-vous system.,Therefore,orexin has been recognized as a major regulator ofvarious behavioral activeties including feeding,normal sleep-wake cycle,sym-pathetic nerve activity. And its epilepsy-related research confirmed that it canenhance GABA currents and orexin-A concentration in cerebrospinal fluid inpatients with repeated seizures is less than one in non-epileptic patients, The-refore, orexin may be associated with seizures or control of epilepse.In order to clarify the role of orexin in epileptic seizure,seizures were in-duced by intraperitoneal injection of kainic acid in this study.Then the expr-essions of prepro-orexin mRNA in rat cortex,hippocampus and hypothalamu-s were detected by using real-time RT PCR and the changes of the prepro-orexin,orexin-A and orexin-B immunoreactive cells and nerve fibers were d-etected by immunohistochemistry at8hours,1,3,7days and chronic relapsin-g time after the termination of epilepsy respectively.The results are as follo-ws:1.The expression of prepro-orexin mRNA by real-time RT PCR:prepro-ore-xin mRNA levels increased in the cortex and the hippocampus conformabl-y,and the maximum was observed in the1d group (relative to the control g -roup,3.170857±0.271and2.788±0.075times respectively).However,it decreased in the hypothalamus,and the minimum was observed in the1d group(0.597±0.020times).2..Immunohistochemical detection:(1),prepro-orexin immunoreactive cells distributed in the hypothalamus and the perifornical nucleus, and the cell count was not remarkably differentbetween the groups.But the curve of the cell count declined overall,especial-ly in the7d group.The prepro-orexin immunoreactive nerve fibers were rar-e and distributed mainly in the hypothalamus,the hypothalamic paraventricu-lar nucleus and hippocampus.(2),orexin-A immunoreactive cells distributed in the hypothalamus and theperifornical nucleus,and decreased remarkably in the8h group compared w-ith other groups.The trend of the cell count reduced first,then relapsed an-d reduced again.The orexin-A immunoreactive nerve fibers were widely dist-ributed in the central nervous system,and increased remarkably in the8h g-roup compared with other groups in addition to1d group. Its trend showe-d increased first,then reduced,and increased again.(3)orexin-B immunoreactive cells distributed in the hypothalamus and theperifornical nucleus. It also distributed dubiously in the hippocampus,mostobviously in the8h group,then the3d group. The trend of the cell countreduced first,then relapsed and reduced again,relapsed finally.It decreased sig-nificantly in the7d group compared with other groups.Orexin-B immunore-active nervous fibers widely distributed in the central nervous system.And t-he trend of their changes was opposite to the cells’.In conclusion,the changes of prepro-orexin mRNA,the orexin immunoreact-ive cells and the immunoreactive fibers after the seizure show that they m-ay be involved in the regulation of epilepsy.And it can help to control sei-zures by increasing orexin’s concentration.