Associative learning down-regulates PKCβ2- and γ-immunoreactivity in astrocytes

We showed previously that associative learning induced a twofold increase in protein kinase Cγ-immunoreactivity (PKCγ-ir) in rabbit CA1 pyramidal neurons, whereas subicular neurons remained unchanged. Here, we investigated the effects of associative learning on PKC-positive astrocytes by determining their numerical density in the CA1 region and the subiculum of naive, pseudoconditioned and trace eyeblink conditioned rabbits. Associative learning induced a 70-80% reduction in the number of PKCβ2- and γ-positive astrocytes in the CA1 region, but not in the subiculum. No changes were found in the number of PKCα- or β1-positive astrocytes in either hippocampal subregion. These results suggest a conditioning-specific downregulation of PKCβ2 and γ in a subset of astrocytes in a brain region where a simultaneous alteration in neuronal PKCγ was evident.