Molecular Brain Research, 19 (1993) 269-276 269 Elsevier Science Publishers B.V. BRESM 70631 Research Reports Quantitative distribution of protein kinase C a,/3, y, and e mRNAS in the hippocampus of control and nictitating membrane conditioned rabbits Ann Marie Craig *, James L. Olds, Bernard G. Schreurs, Andrew M. Scharenberg and Daniel L. Alkon Laboratory of Adaptive Systems, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892 (USA) (Accepted 16 February 1993) Key words: Protein kinase C; Gene expression; In situ hybridization;Hippocampus;Classical conditioning; Rabbit We used oligonucleotide in situ hybridization and film autoradiographyto quantitate the distributions of protein kinase C (PKt~) a,/3, 3', and mRNAs in subregions of rabbit hippocampus. Levels of each of the hippocampal PKC isozyme mRNAs and patterns of their regional distributions were remarkably invariant between individuals. Within stratum pyramidale, the highest levels of PKC a mRNA were in the CA2 region, while PKC/3 mRNA was maximallyexpressed in CA1, and PKC ~ mRNA in CA3; PKC y mRNAwas abundantly expressed throughout Ammon's horn. Previous experiments employingquantitative autoradiographyfor [3H]PDBU(Olds et al., Science, 245 (1989) 866-869) revealed an increase in membrane-bound PKC in the CA1 region of rabbit hippocampus up to 3 days followingclassical conditioning of the nictitating membrane response. We report here that there were no differences in levels of PKC a, /3, y, or E mRNA between conditioned and control rabbits in any hippocampal region one day after training. These data are consistent with the hypothesis that PKC is post-translationally activated and translocated to the membrane during memorystorage. INTRODUCTION Activation of the phospholipid-dependent enzyme protein kinase C (PKC) is one of the critical events in the transduction of many extracellular signals, includ- ing the response of neurons to synaptic stimulation 24. Specific transmitter binding can bring about phospho- lipid hydrolysis and transient intracellular increases in the PKC activators diacylglycerol (DG), Ca 2+, and arachidonic acid (AA). Activation of PKC is generally accompanied by translocation from the cytosol to the membrane 7. PKC activation in neurons can lead to changes in ion channel properties, transmitter release, and transmitter sensitivity t7. Activation of PKC or in- troduction of activated PKC into Hermissenda pho- toreceptors mimics the changes in protein phosphory- lation and reduction of voltage-dependent K + currents which occur during classical conditioning 2'3'13'23. PKC is particularly abundant in the mammalian hippocampus, a structure long known to be involved in memory formation 4°'44 and more recently the site of studies of long-term potentiation (LTP) of synaptic efficacy18. PKC may be activated in hippocampal neu- rons by multiple mechanisms including activation of muscarinic cholinergic and excitatory amino acid re- ceptors 31'46. Injection of PKC into CA1 neurons poten- tiates the synaptic response 15. PKC translocation and activation are associated with and required for induc- tion of LTP in the perforant path and in the Schaffer collateral pathway 1,5,22. A role for PKC in hippocampal memory processes was suggested by changes in the distribution of membrane-bound PKC in the rabbit hippocampus following classical conditioning of the nictitating membrane response (NMR) and in the rat hippocampus following discrimination learning 4'6'31'32'37. This idea is further supported by the observation that Correspondence: A.M. Craig, Present address: Department.of Neuroscience, Universityof Virginia School of Medicine, MR4 Annex, Room 5147, Charlottesville, VA 22908, USA. Fax: (1) (804) 982 4380.