Correlations between hippocampal protein kinase C activity and learning abilities in a spatial reference memory task

Partial learning of a reference memory task induces a decrease in hippocampal cytosolic protein kinase C (PKC) activity with no concomitant changes in the particulate fraction. The particulate PKC activity is correlated with performance (Nogues, Micheau, & Jaffard, 1994). The relationship between the level of training and PKC activity was investigated in the present study. Hippocampal PKC activity was measured after mice were trained for 2, 5, or 12 sessions in a spatial discrimination task in an 8-arm radial maze. No increase in membrane-bound fraction or decrease in cytosolic PKC activity was observed at any stage of learning, although performance was correlated with PKC activity in each subcellular fraction. We sought correlations between performance and the magnitude of the decrease in cytosolic PKC activity, with reference to previously obtained data. The extent of the fall in cytosolic PKC was found to be related to learning abilities rather than to the maximal performance level. Causal explanatory models are proposed to explain these somewhat contradictory data.