The Effect Of Dizocilpine Maleate And Taurine On The Manganese-Induced Cerebrum Neurotoxicity Of Rats

Manganese (Mn) is an essential trace element and an integral component of keyenzymes required for normal biochemical and celluar function in the central nervoussystem (CNS) .However, excess deposition of manganese in the CNS often leadsneurological abnormalities, including manganism, the symptoms of which (hypokinesis,rigidity, and tremor) resemble parkison's disease. The objective of the present studywas to observe the effect of different dosage Mn promoting excitotoxicity in Wistar ratsand to determine the toxic dosage of Mn and to explore the effect of thehistopathological change and glutamatic neuron contents.Meanwhile we have apretreatment with MK-801 (Dizocilpine maleate, MK-801) and taurine in order toobserve the preventive effect on MK-801 and taurine on the activities of GS and PAGand the glutamatic neuron content in the rat striatum and the activities of SDH andNa⁺-K⁺-ATPase in pallium,when Mn posioning occurs.Methods52 wistar rats obtained from the Laboratory Animal Center of Chinese MedicineUniversity, weight (180±10) gram. The rats were housed at (21±2) Celisus degreewith alternating light and dark.After an acclimation period of a week, the experimentstarted in two parts.At first, the aim was to determine the toxic dosage of Mn and toexplore whether MK-801 and taurine can prevent the toxic effects of Mn on the ratscerebrum. 36 Wistar rats were divided into six groups by weight at random. The first group was the control group, the second to fourth groups were Mn poisoning group, thefifth and sixth group were MK-801 and taurine group. The first to fourth groups weregiven peritoneal injection (i.p) of 0．9% NaCl; The fifth, sixth groups were respectivelyinjected MK-801 0．3μmol/kg, Tau 1mmol/kg in abdominal cavity. After two hours, thesecond, third groups were respectively given i.p of 8 , 40μmol/kg MnCl₂;the fourth tosixth groups were given subcutaneous injection of MnCl₂ 200μmol/kg. After 25-daysadministration, the activities of GS and PAG in the rat striatum and the activities ofSDH and Na⁺-K⁺-ATPase in pallium were determined. Na⁺-K⁺-ATPase activity wasmeasured according to the method of Chen et al; the GS activity was detemined byfollowing the formation ofγ-glutamyl hydroxamate by the absorbance of the solution at535nm as Renis described;the brain tissue were extacted to obtain mithchondria bydensity-centrifugation and speed-centrifugation for the activities of SDH and PAG. Thesecond part experiment was pretreatment with MK-801 and taurine in order to observethe preventive effect on MK-801 and taurine on the glutamatic neuron content in the ratstriatum. 16 Wistar rats were divided into four groups by weight at random. The firstgroup was the control group which was given subcutaneous injection of 0．9% NaCl;The second group was given subcutaneous injection of 0．9% NaCl; The third, fourthgroups were respectively injected MK-801 0．3μmol/kg, Tau 1mmol/kg in abdominalcavity, after two hours, they were given subcutaneous injection of MnCl₂200μmol/kg.At the 24h after the administration of MnCl₂,the brain tissue was removedafter the rats were perfused from the left ventricles to with 4% ploymerisatum. Theglutamatic neuron content was determined by immunohistochemical method (SABC) .ResultsAccompanied with the incraseing treadted Mn dosage, the activities of SDH andNa⁺-K⁺-ATPase in pallium decreased, the activities of SDH and Na⁺-K⁺-ATPase inpallium in 200μmol/kg MnCl₂ group decreased significantly with a dose-responserelationship; Accompanied with the incraseing treadted Mn dosage, the activity of PAGin corpora striatum increased and the activity of GS in corpora striatum decreased, in 200μmol/kg MnCl₂ group, the activity of GS in corpora striatum decreasedsignificantly, however, he activity of PAG in corpora striatum increased significantly.Therefore, we took 200μmol/kg as the toxic dosage of Mn.In the pretreatment experiment, when the group that merely administered withManganese compared with the control group, the activities of SDH andNa⁺-K⁺-ATPase in pallium and the activity of GS in corpora striatum decreasedsignificantly; the activity of PAG in corpora striatum increased and the statisticdifference was significant. In the group administered with MK-801, the activities ofSDH and Na⁺-K⁺-ATPase in pallium and the activity of GS in corpora striatumincreased significantly; the activity of PAG in corpora striatum decreased significantly.In the group administered with taurine, the activity of GS in corpora striatum and theactivity of SDH in pallium increased significantly; the activity of Na⁺-K⁺-ATPase ofpallium increased and the statistic difference was significant.After 25-days administration, when the group that merely administered withManganese compared with the control group, the percentage of positive area andintegral optical density of glutamate immunocreative cell in striatum increasedsignificantly; when MK-801 group compared with the group that merely administered,the percentage of positive area and integral optical density of glutamateimmunocreative cell in striatum decreased significantly; when taurine group comparedwith the group that merely administered, the percentage of positive area and integraloptical density of glutamate immunocreative cell in striatum decreased significantly.The histopathlogical change was the mainly change in stratium wiyh opticalmicroscopes. HE stain indicates: The morphology in control group is normal and thecytoplasm of neuron is in pink color and the nucleus can be seen clearly, when thegroup that merely administered with Manganese compared with the control group, themorphology of the neurons is changed, the cell bodies became swelling, cytoplasm andchromatin stained color grow shallow, and the apophysis shortened. When MK-801 andtaurine group compared with the group that merely administered, cytoplasm and chromatin stained color grow deeply, the apophysis in part cell can be seen clearly, thecell bodies size is commonly normal, however the cell bodies in part neuron becameswelling.DiscussionsGlutamate is the most prevalent excitatory neurotransmitter, as a neurotransmitter,which is predominantly formed through "the circuitry of glutamate and glutamine".when the group that merely administered with Manganese compared with the controlgroup, the percentage of positive area and integral optical density of glutamateimmunocreative cell in striatum increased significantly; the activity of GS in corporastriatum decreased significantly; the activity of PAG in corpora striatum increased andthe statistic difference was significant. Mn disrupted glutamate metabolism, which cancontribute exicitotoxic lesions through disrupting "the circuitry of glutamate andglutamine".The results demonstrateds that Mn treatment sinfiantly decrease SDH activity,which decrease in energetic metabolism could be one action that explainsextrapyramidal symptoms described in Mn intoxications. Mn lead to energy depletionsand decrease Na⁺-K`+-ATPase activity, Which promote that manganese mighe bereleased with glutamate from these afferent neuron terminals during stimulation withhigh K⁺ into the synaptic cleft.A non-competitive NMDA-antagonist, MK-801 can inhibit glutamate integrate theNMDA receptor. Taurine is one of neurotransmitter and/or neuromodulator. MK-801and tauine may increase the activities of SDH,Na⁺-K⁺-ATPase and GS and decreasethe glutamatic neuron content in the rat striatum ,which suggest that they have a certainprotective effect on Wistar rats on Mn-induced toxicity.Conclusions1．When the rats were injected low dose Mn for long time, Mn may decrase theactivities of SDH and Na⁺-K⁺-ATPase in pallium. Accompanied with the incraseingtreadted Mn dosage, Mn may decrease the activity of GS in corpora striatum and increase the activity of PAG in corpora striatum ,which led to disrupt glutamatemetabolism.where were a dose-response relationship in dosage Mn promotingexcitotoxicity. Mn might lead to the histopathological change and increase glutamaticneuron contents.2．MK-801 and tauine may increase the activities of SDH,Na⁺-K⁺-ATPase and GSand decrease the glutamatic neuron content in the rat striatum ,which suggest that theyhave a certain protective effect on Wistar rats on Mn-induced toxicity.3．MK-801 may decrease the activity of PAG ,however can not.