Effects Of Melatonin On TGF-β3 Level In Hippocampus Of Rats With Seizures Induced By Kainic Acid

Transforming growth factor beta3 (TGF-β3) is a member of multifunctional cytokines of TGF-βsuperfamily. They act on nearly every type of cell, regulate a variety of basic biological functions, play an important role in cell proliferation and differentiation, embryonic decvelopment, organ formation, tissue repair and apoptosis. TGF-β3 mRNA is found in all areas of the central nervous system (CNS) including cortex, hippocampus, striatum, brainstem, cerebellum and spinal cord. Immunoreactive TGF-β3 is seen in white matter astrocytes, as well as neurons in within the substantia nigra, spinal cord motoneurons, hippocampal pyramidal neurons, dentate gryus granule cells, large cortical neurons with layersⅡ,ⅢandⅤ, and subpopulations of cerebellar Purkinje cells. RNA of the TGF-βRⅠand RⅡhave been reported in adult rodent brain, suggesting that TGF-β3 is capable of exerting biological actions in the CNS in vivo. Biological actions of TGF-βare mediated through its binding to a heteromeric transmembrane receptor complex of two subunits designated RⅠand RⅡwhich are belong to a growing family of receptors with serine/threonine kinase activity. Loss or mutation of components of the TGF-βsignaling pathway leads to numerous diseases. Data shows, abnormal expressions and changes of TGF-βin the CNS have close relationship to the genesis and development of neurodegenerative disease, such as epilepsy, Alzheimer disease, Parkinson's disease, stroke and so on.Melatonin (MT) is a hormone synthesized and secreted by the pineal gland during the night. A number of neuropharmacological effects (such as keeping circadian rhythm, improving sleep, enhancing immunofunction and so on) of melatonin have been observed. Recently, other functions of melatonin have been suggested, including scavenging of free radicals, neuroprotection, and antiepileptic efficacy in various animal models of epilepsy. Most scholars have attached importance to antiepileptic action of melatonin. Our laboratory has found MT could inhibit the epilepsy induced by glutamic aid and coriamyrtin, which may act by reduing the expressions of NR1 and Glu, inhancing the GABA and GABRA1, downregulating the level of cAMP, cGMP and upregulating 5-HT.Although the antiepileptic effect of melatonin has been reported in a number of reports, little is known about the mechanisms underlined its antiepileptic action and the role of TGF-β3 in the epileptogenesis. The objectives of our present work were to study melatonin's antiepileptic properties on kainic acid-induced epilepsy, and to probe the mechanisms of melatonin's antiepileptic role by observing the changes of TGF-β3 level and the protective action on neurons in hippocampus.In our study, the changes of TGF-β3 in the hippocampus of epileptic rats were detected by immunohistochemistry staining method SABC and RT-PCR on the level of cell and gene respectively. The observation of rats'behavior showed that no seizure activity occured in the NS group,butⅢ-Ⅴgrade of seizure can be seen in the KA group and 0-Ⅲgrade in the MT+KA group. Immunohistochemistry staining indicated that TGF-β3 expressed in hippocampus of all groups, we can see immunoreactive neurons in pyramidal cell layer of hippocampus CA1-CA3 and granule cell layer of dentate gyrus in each group. The expression in the KA and MT+KA group is higher than that in the NS group, moreover MT+KA group is higher than KA group, the differences between each group are significantly( P < 0.05). The results of RT-PCR showed the same tendency of changes on the level of TGF-β3 mRNA as it described in the immunohistochemistry. The morphology of TGF-β3 change indicated by immunostaining is coincident with the relative content of mRNA change in hippocampus detected by RT-PCR. Pretreatment with rat, the number of TGF-β3 positive neurons and the relative contents of TGF-β3 mRNA in hippocampus are all increased compare with KA group.All of these suggest that melatonin can improve the seizure activity induced by kainic acid obviously, which may act on the enhancing of TGF-β3 expression in hippocampus to protect the hippocampal neurons from excitoxity damaging caused by kainic acid, to prevent the apoptosis and loss of neurons of hippocampal area CA1 and CA3.