1 (5 isoquinolinesulfonyl) 2 methylpiperazine Animalia B-50/GAP-43 Bovinae PKC Tritium animal cell animal experiment article brain synaptosome controlled study enzyme activity hippocampus learning long term potentiation male memory neuromodulin nonhuman phorbol dibutyrate polymyxin B priority journal protein kinase C protein kinase C inhibitor protein phosphorylation rat staurosporine derivative synaptic membrane task performance training