STIMULATION OF NMDA RECEPTORS ACTIVATES CALPAIN IN CULTURED HIPPOCAMPAL SLICES

The hypothesis that intense stimulation of NMDA receptors activates ca lpain was tested in long-term cultures of hippocampus. Slices prepared from 10-day-old rats were maintained for periods of up to 6 weeks and then assayed for a stable breakdown product that results from the pro teolysis of spectrin by calpain. The breakdown product increased drama tically during the first 24 h after tissue preparation and then decrea sed to a low level that remained unchanged for weeks. NMDA caused a 2- to 3-fold increase in breakdown product that rose linearly with time (5-30 min) and was blocked by the receptor antagonist MK-801. The effe ct of NMDA was the same throughout the culture period and was dependen t upon the concentration of extracellular calcium with no effect at 2 mM and maximal effect at 4 mM calcium. These results indicate that rap id activation of calpain occurs in undamaged hippocampal neurons follo wing stimulation of NMDA receptors.