CELLULAR LOCUS OF THE NITRIC-OXIDE SYNTHASE INVOLVED IN CEREBELLAR LONG-TERM DEPRESSION INDUCED BY HIGH EXTERNAL POTASSIUM CONCENTRATION

The cellular location of the NO-synthase involved in long-term depress ion (LTD) of parallel fiber (PF)-mediated EPSCs induced by raising the external potassium (K) concentration has been investigated by using b oth whole-cell patch-clamp recordings (WCR) of Purkinje cells (PCs) in thin slices in vitro, and reverse transcription followed by polymeras e chain reaction (PCR) applied to mRNAs harvested from these single PC s during WCR. In all tested cells in the control group, a large LTD of PF-mediated EPSCs was induced by perfusing the slices for 3 min with a high (30 mM) K perfusing medium. In a second group of cells for whic h the protein kinase C (PKC) inhibitor peptide 19-36 was added to the intrapipette solution at a concentration of 10 mu M, the LTD following complete wash out of the high K solution was significantly less promi nent than in the control group. Very similar results were also obtaine d when 30 mu M N-G-methyl-L-arginine (L-NMMA) was added to the perfusi ng medium. In contrast, when both the PKC inhibitor peptide 19-36 and L-NMMA were added to the intrapipette solution at a concentration of 1 0 and 30 mu M respectively, no LTD was revealed following wash out of the high K solution. Finally, the PCR amplification of mRNAs harvested from these single PCs during WCR, as well as from granule cells from the same slices, confirms that mRNAs encoding the NO-synthase are expr essed by granule cells, whereas they are not detected in PCs.