In this study, methamphetamine (Meth)- and glutamate (Glu)-mediated intracellular Ca++ (Ca++ i) signals were examined in real time in primary cortical neurons overexpressing an intracellular Ca++ probe, GCaMP5, by adeno-associated viral (AAV) serotype 1. Binding of Ca++ to GCaMP increased green fluorescence intensity in cells. Both Meth and Glu induced a rapid increase in Ca++ i, which was blocked by MK801, suggesting that Meth enhanced Ca++ i through Glu receptor in neurons. The Meth-mediated Ca++ signal was also blocked by Mg++ , low Ca++ or the L-type Ca++ channel inhibitor nifedipine. The ryanodine receptor inhibitor dantrolene did not alter the initial Ca++ influx but partially reduced the peak of Ca++ i. These data suggest that Meth enhanced Ca++ influx through membrane Ca++ channels, which then triggered the release of Ca++ from the endoplasmic reticulum in the cytosol. AAV-GCaMP5 was also injected to the parietal cortex of adult rats. Administration of Meth enhanced fluorescence in the ipsilateral cortex. Using immunohistochemistry, Meth-induced green fluorescence was found in the NeuN-containing cells in the cortex, suggesting that Meth increased Ca++ in neurons in vivo. In conclusion, we have used in vitro and in vivo techniques to demonstrate a rapid increase of Ca++ i by Meth in cortical neurons through overexpression of GCaMP5. As Meth induces behavioral responses and neurotoxicity through Ca++ i, modulation of Ca++ i may be useful to reduce Meth-related reactions.
