LEARNING-SPECIFIC, TIME-DEPENDENT INCREASES IN HIPPOCAMPAL CA2+ CALMODULIN-DEPENDENT PROTEIN-KINASE-II ACTIVITY AND AMPA GLUR1 SUBUNIT IMMUNOREACTIVITY/

Ca2+/calmodulin-dependent protein kinase II (CAMK II) and one of its t arget, lpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), glutamate receptors have been shown to participate in both long-term potentiation (LTP) in the hippocampus, and in spatial, as well as in a variety, of learning paradigms, Recently, we were able to demonstrate that the intrahippocampal infusion of a specific inhibitor of CAMK II (KN62) provoked full retrograde amnesia of an inhibitory avoidance le arning in rats when given immediately, but not 120 or 240 min, after t raining. Furthermore, this task is accompanied by a rapid, selective a nd reversible increase in hippocampal [H-3] AMPA receptor binding. Her e we report the effect of this aversively motivated learning task on C AMK II activity, and AMPA GluR1 subunit phosphorylation and immunoreac tivity in the hippocampus. One trial inhibitory avoidance training is associated with a learning-specific, time-dependent increase (25-78%) in both total and Ca2+-independent activities of CAMK II in the hippoc ampus of rats killed immediately (0 min), but not 120 min, after train ing, In addition, immunoblotting experiments showed an increment in th e amount of the alpha-subunit of CAMK II at 0, 30 and 120 min after tr aining. An increase in the in vitro phosphorylation of alpha- and beta -subunits of CAMK II was also observed in hippocampal synaptosomal mem branes (SPM) of trained rats killed immediately and 30 min post-traini ng. In addition, inhibitory avoidance is accompanied by a 20% increase in GluR1 phosphorylation and a 33% increase in GluR1 immunoreactivity 120 min after training. No significant changes were observed in shock ed animals. Phosphorylation of hippocampal SPM from naive control anim als in conditions suitable for CAMK II activation resulted in a large increase in the density of [H-3] AMPA binding (+ 100%). Taken together , these findings confirm and extend previous data suggesting that CAMK II and AMPA glutamate receptors in the hippocampus participate in the early phase of memory formation of an inhibitory avoidance learning.