DYNAMIC PROPERTIES OF NITRIC-OXIDE RELEASE FROM PARALLEL FIBERS IN RAT CEREBELLAR SLICES

1. Nitric oxide (NO) release following repetitive electrical stimulati on was studied in tile molecular layer of rat cerebellar slices using electrochemical NO probes. 2. In parasagittal slices of the vermis, mo st Purkinje cells showed climbing fibre responses in response to white matter stimulation without accompanying NO release. 3. In frontal sli ces, parallel fibre volley potentials and NO release were elicited con currently by parallel fibre stimulation. 4. The NO release following p arallel fibre stimulation was not affected by blockers of non NMDA, NM DA and metabotropic glutamate receptors. 5. The NO release was reduced significantly (P < 0.001) to 29% of the control level after climbing fibre deafferentation with 3-acetylpyridine treatment. 6. The rate of NO release was roughly proportional to the second or third power of th e stimulus frequency, and to the third power of the extracellular Ca2 concentration. 7. The rate of NO release was not affected by nicardip ine (10 mu M). It was reduced to 87 +/- 4% (n = 5, mean +/- S.E.M.). O f the control level by omega-conotoxin GVIA (0.3 mu M), and to 18 +/- 4%(n = 4) by omega-agatoxin IVB (0.3 mu M). 8. Tetanic parallel fibre stimulation potentiated NO release by 24 +/- 5% (n = 5). 9. These data indicate that NO is derived mainly from parallel fibres. The relation ship between NO release and cerebellar synaptic plasticity is discusse d.