Protein synthesis required for long-term memory is induced by PKC activation on days before associative learning

Abstract

Protein synthesis has long been known to be required for associative learning to consolidate into long-term memory. Here we demonstrate that PKC isozyme activation on days before training can induce the synthesis of proteins necessary and sufficient for subsequent long-term memory consolidation. Bryostatin (Bryo), a macrolide lactone with efficacy in subnanomolar concentrations and a potential therapeutic for Alzheimer's disease, is a potent activator of PKC, some of whose isozymes undergo prolonged activation after associative learning. Under normal conditions, two training events with paired visual and vestibular stimuli cause short-term memory of the mollusc Hermissenda that lasts Ϸ7 min. However, after 4-h exposures to Bryo (0.25 ng͞ml) on two preceding days, the same two training events produced long-term conditioning that lasted >1 week and that was not blocked by anisomycin (1 g͞ml). Anisomycin, however, eliminated long-term memory lasting at least 1 week after nine training events. Both the nine training events alone and two Bryo exposures plus two training event regimens caused comparably increased levels of the PKC ␣-isozyme substrate calexcitin in identified type B neurons and enhanced PKC activity in the membrane fractions. Furthermore, Bryo increased overall protein synthesis in cultured mammalian neurons by up to 60% for >3 days. The specific PKC antagonist Ro-32-0432 blocked much of this Bryo-induced protein synthesis as well as the Bryo-induced enhancement of the behavioral conditioning. Thus, Bryo-induced PKC activation produces those proteins necessary and sufficient for long-term memory on days in advance of the training events themselves.bryostatin ͉ PKC isozymes T he requirement of protein synthesis for long-term memory has been demonstrated over several decades for a variety of memory paradigms (1-14). It was originally shown that druginduced inhibition of protein synthesis (e.g., with 5-propyluracil or anisomycin) blocked long-term memory when this inhibition occurred during a critical time interval after the training paradigm (9). It has remained a mystery as to what specific, critical proteins were so essential for memory consolidation and how their molecular regulation was so necessary for long-lasting memory storage.In many species the formation of long-term associative memory has also been shown to depend on translocation, and thus activation, of protein kinase C (PKC) isozymes to neuronal membranes. PKC activation has been shown to occur in single identified type B cells of the mollusc Hermissenda (15) with Pavlovian conditioning and a variety of mammalian associative learning protocols (16)(17)(18). Furthermore, a high-affinity substrate of the ␣-isozyme of PKC, calexcitin (CE) (19), was found within single identified type B cells to show Pavlovianconditioning-dependent increases of phosphorylation and absolute quantity (20).Consistent with these findings, administration of the potent PKC activator bryostatin (Bryo) enhanced rat spatial maze learning (21). Bryo, a macrolide lactone,...

Bryostatin Enhancement of Memory inHermissenda

“…The anisomycin-bryostatin study confirmed the results of other studies Alkon et al, 2005) showing that protein synthesis is involved in memory storage and its subsequent recall. Animals that had received 2-paired TEs plus bryostatin (0.25 ng/ml) and then were tested for recall at 4 h showed positive CRs with the CS alone.…”

“…The dose response results with Hermissenda were congruous with the published data for several model systems (Favit et al, 1998;Wender et al, 1998;Etcheberrigaray et al, 2004;Scioletti et al, 2004;Alkon et al, 2005). Subnanogram concentrations of bryostatin administered before paired associative conditioning up-regulated PKC activity, and specifically for Hermissenda, enhanced both acquisition and retention initiated by suboptimal paired CS/US training regimes.…”

“…dolylmaleimide-XI, Bis-XI) confirmed the hypothesis that bryostatin-enhanced CM occurred through PKC activation (Burry, 1998;Alkon et al, 2005). Due to the specificity of Ro-32, it can be stated conclusively that PKC-␣ was the predominant isoform affected (a 10-fold selectivity; Wilkinson et al, 1993).…”

“…In addition to stimulating PKC-induced outgrowth of nerve growth factor-dependent neurites (Burry, 1998), it favors the generation of the nontoxic form of soluble ␣-amyloid precursor protein by differentially activating the isoform, PKC-␣ (Etcheberrigaray et al, 2004). Bryostatin has recently been reported to enhance spatial maze learning in rats (Sun and Alkon, 2005), and learning in rabbits experiencing tone and nictitating membrane associative training paradigms (as reported in Alkon et al, 2005). Its effects can be readily inhibited by many bisindolymaleimide compounds (Burry, 1998).…”

Poststroke neuronal rescue and synaptogenesis mediated in vivo by protein kinase C in adult brains

“…Bryostatin-1, which crosses the blood-brain barrier when administered peripherally (28), produces a relatively selective activation of the PKC isozyme, which is neuroprotective (29)(30)(31) and has a lower median effective dose than PKC␦ for bryostatin-1 in its translocation (thus activation), whereas PKC␦ is most likely involved in ischemic injury during ischemia-reperfusion (32)(33)(34). We recently showed that PKC activation with bryostatin-1 enhanced exactly those synaptogenesis, presynaptic/postsynaptic ultrastructural specialization, and protein synthesis functions involved in rat maze learning and memory (20,35). PKC activation has at least two actions that may be relevant to PKC signal processing: activation of PKC isozymes at low concentrations and protection of active, membrane-bound PKC from degradation under stress.…”