Inositol 1-phosphate formation in long-term potentiation and kindling.

Long-term potentiation (LTP) in the CA3 hippocampal subfield, elicited in vivo, produced significant increases in basal and in carbachol- and noradrenaline-induced hydrolysis of phosphatidylinositol-4,5-biphosphate (PtdIns(4,5)P2) as measured by the accumulation of InsP1 in hippocampal slices in vitro. Kindling, however, resulted in significant decreases in basal and in carbachol- and noradrenaline-induced accumulation of InsP1 in hippocampal slices. N-Methyl-D-aspartate (NMDA) receptors do not directly alter the hydrolysis of PtdIns(4,5)P2 in either LTP or kindling. These results demonstrate that LTP and kindling are associated with opposite alterations in efficacy of the main receptors mediating the hydrolysis of PtdIns(4,5)P2.