Sinner B, Friedrich O, Zink W, Zausig Y, Graf BM
Anesthesia & Analgesia. November 2011.
In the immature brain, neuronal Ca(2+) oscillations are present during a time period of high plasticity and regulate neuronal differentiation and synaptogenesis. In this study we examined the long-term blockade of hippocampal Ca(2+) oscillations, the role of the N-methyl-d-aspartate (NMDA) receptors and the effects of S(+)-ketamine on neuronal synapsin expression.
Hippocampal neurons were incubated at day 15 in culture with the specific NMDA receptor antagonists dizocilpine (MK 801, 100 μM) or S(+)-ketamine (3 μM to 25 μM) for 24 hours. Terminal-deoxynucleotidyl-transferase (TUNEL) and activated caspase3 were used to detect apoptotic neurons. Ca(2+) oscillations were detected after loading the neurons with the Ca(2+)-sensitive dye fura-2AM, and dual wavelength excitation fluorescence microscopy was performed. Ca(2+)/calmodulin kinase II (CaMKII) was measured using Western blots. Synapsin was identified with confocal antisynapsin immunofluorescence.
Blocking the NMDA receptor with MK 801 or 25 μM S(+)-ketamine resulted in a significant increase in apoptotic neurons. MK 801 led to a significant increase in cytosolic Ca(2+) concentration and reduction of the amplitude and frequency of the Ca(2+) oscillations. Similar to MK 801, the long-term application of S(+)-ketamine resulted in a significant increase in cytosolic Ca(2+) concentration 24 hours after washout. This was associated with a down-regulation of the CaMKII and a reduction of the synapsin 24 hours after washout.
Neuronal Ca(2+) oscillations mediate neuronal differentiation and synaptogenesis via activating CaMKII. By acting via the NMDA receptor, S(+)-ketamine exerts its toxic effect through the suppression of neuronal Ca(2+) oscillations, down-regulation of the CaMKII, and consecutively reduced synaptic integrity.