The effects of recombinant mouse stem cell factor (rmSCF) on paired-pulse facilitation (PPF) and long-term potentiation (LTP) in the mossy fiber (MF)-CA3 pathway were examined in mouse hippocampal slices by recording field EPSPs. When PPF was measured before and 30 min after tetanic stimulation, the initial PPF positively correlated with the amplitude of LTP and negatively correlated with changes in PPF (PPF after LTP minus initial PPF), indicating a presynaptic component in MF-CA3 LTP. Bath application of rmSCF for 30 min also produced negative correlation between initial PPF and changes in PPF after rmSCF, suggesting common mechanisms of the LTP- and rmSCF-induced modulation of PPF. The rmSCF-induced negative correlation was abolished by simultaneous perfusion with K252a, a receptor tyrosine kinase inhibitor, and by wortmannin, a phosphatidylinositol-3′-kinase inhibitor. Although SCF activates phospholipase A2 (PLA2) and diacylglycerol (DAG) lipase to produce arachidonic acid (AA) in mast cells, mepacrine, a PLA2 inhibitor, but not RHC80267, a DAG lipase inhibitor, abolished the negative correlation. The induction of LTP was prevented by perfusion with rmSCF started 30 min before tetanus, while preincubation of slices with antibody for SCF receptor, c-kit, blocked LTP, suggesting that the intrinsic SCF is involved in the induction of LTP and the blockade of LTP by rmSCF might be due to an occlusion of SCF/c-kit signaling. In addition, since c-kit is expressed on the postsynaptic CA3 neurons but not on the MF terminals in mice, effects of rmSCF on PPF may be mediated by the PLA2-induced AA acting as a retrograde messenger.
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