Uticaj elektromagnetnog polja (0,5 mT, 50 Hz) na motorno ponašanje, parametre oksidativnog stresa i morfološke karakteristike mozga nakon eksperimentalno izazvane moždane ishemije na modelu pustinjskog miša

Abstract

U današnje vreme, jedna od najčešćih bolesti koja pogaña celokupno društvo je moždani udar, koji može biti uzrokovan moždanom ishemijom. Osim što u velikom procentu dovodi do smrti, posledice moždanog udara su najčešće trajne i za njih ne postoji efikasna terapija. Još jedna karakteristika modernog doba je razvitak elektronske industrije i primena sve raznovrsnijih električnih ureñaja, a samim tim i povećanje stepena zagañenja “elektromagnetnim smogom”. Povećano prisustvo niskofrekventnih elektromagnetnih polja (EMP) je privuklo interesovanje velikog broja naučnika te su ispitivani njegovi efekti, izmeñu ostalog i na funkcionalne karakteristike centralnog nervnog sistema. Na osnovu poznatih činjenica o njegovom dejstvu možemo pretpostaviti da ovo polje utiče i na razvoj patofizioloških dogañaja i oporavak u uslovima moždane ishemije. Cilj naše studije je bio da ispitamo da li elektromagnetno polje (0,5 mT, 50 Hz, u trajanju od 7 dana) utiče na hipermotorno ponašanje pustinjskih miševa izazvano 10-min globalnom moždanom ishemijom i to 1., 2., 4. i 7. dana (neposredan efekat EMP), kao i 14. dana nakon reperfuzije (odloženi efekat EMP). Takoñe, na modelu moždane ishemije smo ispitali da li primenjeno EMP utiče na parametre oksidativnog stresa, koji su inače povišeni nakon moždane ishemije, u pojedinim regionima mozga 7. i 14. dana nakon reperfuzije. Praćen je i uticaj EMP na morfološke promene u najosetljivijim strukturama mozga (hipokampus, striatum i kora velikog mozga) izazvane ishemijom 7. i 14. dana nakon reperfuzije i morfometrijskom analizom su kvantifikovane promene na neuronima i glijalnim ćelijama. Ponašanje eksperimentalnih životinja je registrovano u trajanju od 60 minuta u testu otvorenog polja - “open field”-u. Pokazano je da 10-min ishemija indukuje značajno povećanje motorne aktivnosti (lokomocija, stereotipija i rotacije) do 4. dana nakon reperfuzije. Izlaganje eksperimentalnih životinja EMP je inhibiralo razvitak hipermotorne aktivnosti izazvane ishemijom i to značajno u prva dva dana nakon reperfuzije kada je i postishemijska hiperaktivnost najuočljivija. Motorna aktivnost ovih pustinjskih miševa je bila značajno povećana u poreñenju sa kontrolnom grupom samo prvog dana nakon reperfuzije. Biohemijski su odreñeni parametri oksidativnog stresa (NO, O2-, SOD, ILP) u hipokampusu, striatumu i kori prednjeg mozga. Ishemija dovodi do povećanja oksidativnog stresa u svim ispitivanim strukturama mozga i to kako 7. tako i 14. dana nakon reperfuzije, a vrednosti za SOD ostaju na kontrolnom nivou. EMP takoñe povećava produkciju slobodnoradikalskih vrsta 7. dana (neposredni efekat EMP) ali u značajno većoj meri nego ishemija, kao i aktivnost SOD. Sedam dana nakon završetka izlaganja (odloženi efekat EMP) izmerene vrednosti parametara oksidativnog stresa su na nivou kontrolnih. Ishemični pustinjski miševi izloženi EMP imaju povećane vrednosti merenih parametara oksidativnog stresa 7. dana nakon reperfuzije (neposredni efekat EMP), ali u znatno manjoj meri nego jedinke ishemične grupe ili grupe izložene EMP. Parametri oksidativnog stresa u mozgu ishemičnih pustinjskih miševa izloženih EMP su na nivou kontrolnih 14. dana nakon reperfuzije. Primenom stereoloških metoda, utvrñeni su volumeni striatuma i hipokampusa, volumenska gustina oštećenih neurona i astrocita, kao i broj mikroglijalnih ćelija po jedinici površine u hipokampusu. Izlaganje EMP nije dovelo do morfoloških promena u ispitivanim strukturama, dok je 10-min globalna moždana ishemija dovela do ćelijske smrti u najvećoj meri u CA1 regionu hipokampusa. Ishemični pustinjski miševi izloženi EMP su imali znatno niži stepen propalih ćelija i veći odgovor astrocita i mikroglijalnih ćelija nego postishemijski pustinjski miševi bez izlaganja 7. dana nakon reperfuzije (neposredni efekat EMP). Sličan odgovor je zapažen i 14. dana nakon reperfuzije (odloženi efekat EMP). Rezultati ovih istraživanja su pokazali da primenjeno EMP (0,5 mT, 50 Hz) smanjuje motornu hiperaktivnost izazvanu 10-min globalnom moždanom ishemijom modulacijom procesa koji leže u osnovi ovakvog ponašanja. Takoñe, EMP smanjuje oksidativni stres izazvan globalnom moždanom ishemijom i na taj način smanjuje moguće negativne posledice koje slobodnoradikalske vrste imaju u mozgu. EMP pokazuje i neuroprotektivnu ulogu u hipokampusu, najosetljivijoj strukturi na ishemijsko oštećenje, redukujući broj oštećenih neurona i aktivirajući astrocite i mikroglijalne ćelije.

Nowadays, one of the most common diseases, which affect the whole society, is brain stroke, which can be caused by cerebral ischemia. Beside high mortality rate, consequences of brain stroke are often permanent without appropriate treatment. Another hallmark of modern society is development of electronic industry and usage of diverse electron devices, therefore increasing degree of pollution with “electromagnetic smog”. The increased presence of extremely low frequency magnetic fields (ELF-MF) has attracted the interest of many scientists to explore its effects, among others, on functional properties of central nervous system. Based on the known facts of its action, we can propose that this field affects development of pathophysiological events and recovery in conditions like cerebral ischemia. The purpose of this study was to determine whether ELF-MF (0.5 mT, 50 Hz, continuous exposue during 7 days) affects hypermotor activity of gerbils, induced by 10-min global cerebral ischemia on the 1st, 2nd, 4th and 7th day (immediate effect) as well as on the 14th day after reperfusion (delayed effect). Also, on this model we examined whether applied ELF-MF affect oxidative stress parameters, otherwise increased after cerebral ischemia, in some brain regions on the 7th and 14th reperfusion day. Also, we examined effect of ELF-MF on morphological changes in the most vulnerable structures of brain (hippocampus, striatum and forebrain cortex) induced by ischemia on the 7th and 14th reperfusion day, as well as performed quantification of this changes in neurons and glial cells. Animal behaviour was monitored for 60 min in the open field. It was shown that the 10-min global cerebral ischemia per se induced a significant motor activity increase (locomotion, stereotypy and rotations), and consequently immobility decrease until day 4 after reperfusion, compared to control gerbils. Exposure to ELF-MF inhibited development of ischemiainduced motor hyperactivity during the whole period of registration, but significantly in the first 2 days after reperfusion, when the postischemic hyperactivity was most evident. Motor activity of these gerbils was still significantly increased compared to control ones, but only on the 1st day after reperfusion. Parameters of oxidative stress (NO, O2-, SOD, ILP) were determined in hippocampus, striatum and forebrain cortex applying biochemical assays. Ischemia per se caused increasing of oxidative stress in all examined structures on the 7th and also 14th reperfusion day with SOD values on the control level. ELF-MF also increased production of free radical species on the 7th day (immediate effect of ELF-MF) but in higher degree then ischemia, as well as, activity of SOD. 7 days after cessation of exposure (delayed effect of ELF-MF) measured values for all parameters were at the control levels. Ischemic gerbils exposed to ELF-MF had increased values of parameters of oxidative stress on the 7th reperfusion day (immediate effect of ELF-MF) but to a lesser extent than ischemic animals or animals exposed to ELF-MF. On the 14th reperfusion day, parameters of oxidative stress in the brain of ischemic gerbils exposed to ELFMF were at the control levels. Applying stereological methods, histological evaluation of changes in the hippocampus was done determining its volume, volume density of degenerating neurons and astrocytes, as well as the number of microglial cells per unit area. ELF-MF per se did not induce any morphological changes in the examined brain structures, while 10-min global cerebral ischemia led to neuronal death, especially in CA1 region of the hippocampus, as expected. Ischemic gerbils exposed to ELF-MF had significantly lower degree of cell loss in the examined structure and greater response of astrocytes and microglial cells than postischemic gerbils without exposure on the 7th day after reperfusion (immediate effect of ELF-MF). Similar response was observed on the 14th day after reperfusion (delayed effect of ELF-MF), however differences in measured parameters were not significant. Results of this study revealed that the applied ELF-MF (0.5 mT, 50 Hz) decreased motor hyperactivity induced by the 10-min global cerebral ischemia, via modulation of the processes that underlie this behavioural response. Also, ELF-MF decreased oxidative stress induced by global cerebral ischemia thus decreasing possible negative consequences which free radical species have in the brain. Applied ELF-MF has possible neuroprotective function in the hippocampus, the most sensitive brain structure in the model of global cerebral ischemia, through reduction of neuronal death and activation of astrocytes and microglial cells.