REPEATED NMDA RECEPTOR ACTIVATION INDUCES DISTINCT INTRACELLULAR CALCIUM CHANGES IN SUBPOPULATIONS OF STRIATAL NEURONS IN-VITRO

The mechanisms underlying long-term calcium changes evoked by excitato ry amino acids have not been previously examined in striatal neurons. Fura-2 fluorescence measurements were used to examine intracellular ca lcium concentration ([Ca2+]i) changes due to repeated N-methyl-D-aspar tate (NMDA) receptor activation, in primary cultures of murine striata l neurons. Three applications of 200 muM NMDA (for 2 min, each applica tion separated by 7 min), in 0 magnesium-containing artificial cerebra l spinal fluid. elicited three distinct responses. In 50 +/- 8% of the NMDA-responsive neurons, no persistent increases in [Ca2+]i (final [C a2+]i less-than-or-equal-to 150% baseline) were observed. while in 33 +/- 7% and 17 +/- 3% of the cells, sustained (peak response > final [C a2+]i > 150% baseline) and uncontrolled increases (final [Ca2+]i > pea k response) were observed. respectively. NMDA-responsive neurons that were intensely immunoreactive for the calcium binding protein calbindi n-D28k never exhibited uncontrolled increases in [Ca2+]i. Removal of e xtracellular Ca2+ significantly attenuated sustained, but not uncontro lled, increases in [Ca2+]i; sustained increases in some neurons were a lso attenuated by application of verapamil (100 muM) or MK-801 (1 muM) . Pre-treatment of striatal neurons with the protein kinase C blocker sphingosine (20 muM), virtually eliminated the development of sustaine d or uncontrolled increases in [Ca2+]i. These findings suggest that sp ecific intracellular mechanisms regulate the distinct (Ca2+]i response s of subpopulations of striatal neurons to repeated NMDA receptor acti vation.