Involvement of hippocampal PKCβI isoform in the early phase of memory formation of an inhibitory avoidance learning

Abstract

Several evidences demonstrate that protein kinase C (PKC) is involved in hippocampal long-term potentiation (LTP) and in different forms of learning, including inhibitory avoidance training in rats. Here, we evaluated the levels of conventional PKC isozymes (α, βI, βII, γ) in synaptic plasma membrane (SPM) fractions isolated from hippocampus of rats subjected to a one-trial inhibitory avoidance paradigm. At 0, 30 and 120 min after training, there was a significant increase in the total amount of PKCβI. Densitometric analysis of the immunoblots showed an increase of 142±11% at 0 min, 193±16% at 30 min and 156±6% at 120 min after training relative to shocked control values. No changes were found in PKCβI levels in SPM fractions of the shocked animals relative to naive control values. No training-specific increments in the levels of PKCα, βII and γ were observed at any time point tested. However, an increase in PKCγ levels was found in trained and shocked animals sacrificed 120 min after each experimental procedure. In addition, bilateral microinjections of a fairly selective inhibitor of PKCβI isozyme into the CA1 of the dorsal hippocampus produced amnesia when given 10 min before training, or 50, 110, but not 170 min, after training. Thus, the present findings demonstrate the participation of PKCβI in the early synaptic events responsible for the acquisition and consolidation of an inhibitory avoidance learning, and suggest a putative role of this presynaptic isozyme on the enhanced PKC-dependent B-50/GAP-43 phosphorylation previously detected by us during this associative learning.