LONG-TERM EFFECT OF EARLY SEIZURE-LIKE DISCHARGE ON ALTERATION OF SPONTANEOUS EXCITATORY POSTSYNAPTIC CURRENT AND INTRACELLULAR CALCIUM IN CULTURED DEVELOPING RAT CORTICAL NEURONS

Objectives: The aim of this work was to study the long-term changes induced in young rat cortical neuronal cultures by transient exposure to a Mg2±free treatment.

Methods: At cultured day 6, three groups were created based on the mediums they were transiently exposed to: control group 1 (CONT1) was exposed to Dulbecco's Modified Eagle's Medium (DMEM), control group 2 was exposed to a physiological solution (PS), and the magnesium-free physiological solution group (MGFPS) was exposed to the same medium as CONT2 except for the removal of magnesium. Following a 3h exposure, the amplitude and frequency of spontaneous excitatory postsynaptic currents (sEPSC) were recorded and intracellular calcium concentrations ([Ca2+]I) were determined.

Results: Compared to the CONT1 and CONT2 groups, the MGFPS group displayed a significantly greater amplitude (at d6, d7, d9, and d12) and frequency (at d6, d7, and d9) of sEPSC (p<0.05). Also, both the resting and peak intracellular calcium levels were significantly greater in the MGFPS group at day 6, 7, 9, 12 and 17 (p<0.05). The rise time (time from resting level to peak level of intracellular calcium following NMDA stimulation) was significantly shorter in the MGFPS group at culture day 7 and 17 and significantly longer at culture day 12 (p<0.05). Finally, we compared the percentage of cortical neurons expressing neuronspecific enolase (NSE) and found that there were no significant differences in the number of NSE positive neurons among three group at day 7, 12, and 17.

Conclusion: Our results suggests that there are long-term changes in sEPSCs and [Ca2+]i in cultured rat cortical neurons following exposure to Mg2±free environment.