Variations in elemental compositions of rat hippocampal formation between acute and latent phases of pilocarpine-induced epilepsy: an X-ray fluorescence microscopy study

Abstract

There is growing experimental evidence that tracing the elements involved in brain hyperexcitability, excitotoxicity, and/or subsequent neurodegeneration could be a valuable source of data on the molecular mechanisms triggering or promoting further development of epilepsy. The most frequently used experimental model of the temporal lobe epilepsy observed in clinical practice is the one based on pilocarpine-induced seizures. In the frame of this study, the elemental anomalies occurring for the rat hippocampal tissue in acute and silent periods after injection of pilocarpine in rats were compared. X-ray fluorescence microscopy was applied for the topographic and quantitative elemental analysis. The differences in the levels of elements such as P, S, K, Ca, Fe, Cu, and Zn between the rats 3 days (SE72) and 6 h (SE6) after pilocarpine injection as well as naive controls were examined. Comparison of SE72 and control groups showed, for specific areas of the hippocampal formation, lower levels of P, K, Cu, and Zn, and an increase in Ca accumulation. These results as well as further analysis of the differences between the SE72 and SE6 groups confirmed that seizure-induced excitotoxicity as well as mossy fiber sprouting are the mechanisms involved in the neurodegenerative processes which may finally lead to spontaneous seizures in the chronic period of the pilocarpine model. Moreover, in the light of the results obtained, Cu seems to play a very important role in the pathogenesis of epilepsy in this animal model. For all areas analyzed, the levels of this element recorded in the latent period were not only lower than those for controls but were even lower than the levels found in the acute period. The decreased hippocampal accumulation of Cu in the phase of behavior and EEG stabilization, a possible inhibitory effect of this element on excitatory amino acid receptors, and enhanced seizure susceptibility in Menkes disease (an inherited Cu transport disorder leading to Cu deficiency in the brain) suggest a neuroprotective role rather than neurodegenerative and proconvulsive roles of Cu in pilocarpine-induced epilepsy.

Various ketogenic diets can differently support brain resistance against experimentally evoked seizures and seizure-induced elemental anomalies of hippocampal formation

“…The role of Zn in seizures and epilepsy is still not well known. Many reports, including this as well as our previous studies, showed that the level of Zn decreased as a result of seizure activity [26,[34][35][36]. Within hippocampus Zn ions are localized in the large terminals of mossy fibers of dentate granule cells [37].…”

The influence of the ketogenic diet on the elemental and biochemical compositions of the hippocampal formation

“…According to different reports, Zn is considered as a seizure-promoting or as an anticonvulsant factor [31][32][33]. From the other side, its hippocampal levels change as a result of seizures [23][24][25][34][35][36]. Our previous study carried out on the rat pilocarpine model showed, moreover, that hippocampal areal density of Zn changes with time passing from the induction of seizures [18,20].…”

“…The hippocampal level of Ca increases as a result of seizures [23][24][25]. Epileptic seizures induce excessive glutamate release which activates postsynaptic NMDA receptors and triggers receptor-mediated Ca 2+ ion influx [37].…”

“…For the analysis of distribution and accumulation of selected elements within the hippocampal formation, X-ray fluorescence microscopy (XRFM) was used, while biochemical evaluation of particular hippocampal areas was done by applying synchrotron Fourier transform infrared microspectroscopy (FTIRM). Both techniques have been successfully applied in our previous studies concerning the mechanisms leading to epilepsy which were carried out mostly on the pilocarpine model of seizures [22][23][24][25][26][27][28][29]. Examining seizure-induced elemental changes of the hippocampal formation, we were able to follow the processes of excitotoxicity and mossy fiber sprouting occurring in this brain area [18][19][20].…”

Elemental and Chemically Specific X-ray Fluorescence Imaging of Biological Systems

“…213 Their XFI results have confirmed the colocalization of elevated levels of Fe, Cu, and Zn within human plaques associated with AD 214 and have also identified significant differences in the extent of metal accumulation between several mouse lines used in AD research. 215 Other examples of the use of XFI include investigation of Zn distribution in the hippocampus in relation to memory loss and delayed neurodegeneration associated with stroke, 216 epilepsy, 217−220 and mechanical brain injury. 221 …”