Involvement of hippocampal PKC beta I isoform in the early phase of memoryformation of an inhibitory avoidance learning

Several evidences demonstrate that protein kinase C (PKC) is involved in hi ppocampal long-term potentiation (LTP) and in different forms of learning, including inhibitory avoidance training in rats. Here, we evaluated the lev els of conventional PKC isozymes (alpha, beta I, beta II, gamma) in synapti c plasma membrane (SPM) fractions isolated from hippocampus of rats subject ed 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 PKC beta I. 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 traini ng relative to shocked control values. No changes were found in PKC beta I levels in SPM fractions of the shocked animals relative to naive control va lues. No training-specific increments in the levels of PKC alpha, beta II a nd gamma were observed at any time point tested. However, an increase in PK C gamma levels was found in trained and shocked animals sacrificed 120 min after each experimental procedure. In addition, bilateral microinjections o f a fairly selective inhibitor of PKC beta I isozyme into the CA1 of the do rsal hippocampus produced amnesia when given 10 min before training, or 50, 110, but not 170 min, after training. Thus, the present findings demonstra te the participation of PKC beta I 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 PK C-dependent B-50/GAP-43 phosphorylation previously detected by us during th is associative learning. (C) 2000 Elsevier Science B.V. All rights reserved .