Involvement of a Protein Kinase C-dependent Process in Long-term Potentiation Formation in Guinea Pig Superior Colliculus Slices

Superior colliculus (SC) slices were prepared from guinea pig. Electrical stimulation was applied to the optic layer (OL) of the SC slices and the postsynaptic potential (PSP) was evoked in the superficial grey layer (SGL) of the SC. Tetanic stimulation to the OL evoked long-term potentiation (LTP) in the PSP. To investigate the involvement of the protein kinase C (PKC) system on the LTP formation in the SC, the effects of PKC activator (phorbol ester) and PKC inhibitors (polymyxin B, melittin and H-7) on the LTP formation have been studied. Application of phorbol ester to the medium at concentrations between 10(-8) and 10(-10) M increased the amplitude of the PSP. On the other hand, the presence of phorbol ester at a concentration of 10(-6) M increased the glutamate release from the SGL slices. Tetanic stimulation which could not induce LTP by itself could elicit LTP during application of phorbol esters at the low concentration (3 X 10(-12) M). PKC inhibitors such as polymyxin B (10(-7) M), melittin (10(-8) M) and H-7 (10(-4) M) prevented LTP formation. When H-7 was applied once after LTP was formed, the enhanced PSP reduced to the original level. These results strongly indicate the involvement of PKC system on the LTP formation in the SC slices.