Protein kinase inhibitors disrupt memory formation in two chick brain regions

Novel effects on memory observed following unilateral intracranial administration of okadaic acid, cyclosporin A, FK506 and [MeVal4]CyA

The involvement of protein phosphatases and peptidyl-prolyl cis/trans isomerases (PPIases) in memory formation in the chick has previously been investigated using a single-trial learning task. In these studies, inhibitory agents were administered bilaterally directly to a critical area of the chick brain. These studies are now extended to investigate whether similar effects are obtained if the drugs are administered unilaterally. All of the effects reported previously following bilateral administration of okadaic acid (OA), cyclosporin A (CyA), FK506 and [MeVal(4)]CyA can be attributed to their action in just one hemisphere. OA, at a concentration known to selectively inhibit PP2A in vitro (0.5 nM) results in permanent memory loss from 30-40 min post-training when injected in the left hemisphere, but has no effect when injected in the right hemisphere. A higher concentration of OA (100 nM), which inhibits both PP2A and PP1 in vitro, has a similar effect in the left hemisphere but causes a transient period of memory loss from 10-20 min post-training when injected in the right hemisphere. CyA (5 nM and 20 nM), which inhibits both PP2B and PPIase activity, causes permanent memory loss from 60 min post-training when injected into the left hemisphere, an effect also observed following administration of FK506 (20 nM), which also inhibits PP2B and PPIase activity, and [MeVal(4)]CyA (5 nM), which inhibits PPIase activity but not PP2B activity. Administration of CyA (20 nM) and FK506, but not [MeVal(4)]CyA, in the right hemisphere leads to a transient period of memory loss from 10-20 min post-training. These results confirm significant roles for phosphatases and PPIases in memory processing but challenge previous conclusions drawn on the basis of bilateral drug administration protocols.

The role of PKA, CaMKII, and PKC in avoidance conditioning: permissive or instructive?

This article explores the causal and correlative relationships between kinases and learning and memory. Specifically, the contributions of three kinases-protein kinase A (PKA), calcium calmodulin-dependent kinase II (CaMKII), and protein kinase C (PKC)-are assessed during the consolidation phase of avoidance conditioning. The following sources of evidence are considered: inhibitor data, activity monitoring, and transgenic studies. An exhaustive effort is made to address several issues regarding the participation of these kinases in (a) posttraining timing and magnitude, (b) location across many brain regions, and (c) the use of multiple pharmacological agents and assays. In addition, this article attempts to integrate the behavioral data with the purported role of kinases in long-term potentiation (LTP).

Ethanol-induced decrease of developmental PKC isoform expression in the embryonic chick brain

Prenatal ethanol exposure can cause a number of physiological deficits known as fetal alcohol syndrome (FAS). Because protein kinase C (PKC) regulates the cell cycle and has been linked to growth, we examined the effect of ethanol on PKC isoform expression in a developing chick brain. Ethanol exposure causes decreased head weight in chickens at day 5 in a dose-dependent manner and a decreased brain weight at days 7 and 10 at an ethanol concentration of 1.0 g/kg. Antibodies specific for PKC-alpha, beta, gamma, delta, epsilon, iota, lambda, mu and zeta were used to examine ethanol's effect on PKC expression in the growth-suppressed brain at days 5, 7 and 10 of development. Only four of the PKC isoforms tested are expressed in the chick brain prior to day 10: alpha, gamma, epsilon, and iota. PKC-alpha, gamma, and epsilon are developmentally increased during the time period studied. Ethanol causes a decreased expression of PKC-alpha on days 5, 7 and 10 and a decreased expression of PKC-gamma on days 7 and 10. Ethanol causes a decreased expression of PKC-epsilon only on day 7. PKC-iota expression is unchanged over the developmental times studied and ethanol exposure has no effect on PKC-iota expression. These data suggest that only specific PKC isoforms are developmentally expressed in the embryonic chick brain and that ethanol may inhibit the expression of those PKC isoforms that are developmentally regulated.

Changes in phosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) in processing of short-term and long-term memories after passive avoidance learning

Characteristic autophosphorylation of calcium/ calmodulin-dependent protein kinase II (CaMKII) and its consequences have made this kinase an interesting target in studying the molecular pathway for important neuronal functions including learning and memory formation. In this article, we use immunoprecipitation and immunoblotting methods to detect changes in phosphorylation of CaMKII during memory formation in 1-day-old chicks trained in a single trial passive avoidance task. A 60-kDa protein has been immunoprecipitated from the chick brain with an anti-rabbit CaMKII antibody. This protein shows strong and specific immunoactivities with antibodies against the calmodulin binding site of CaMKII, and the N and C terminals of beta-CaMKII. Commercially available anti-phosphoserine and anti-phosphothreonine antibodies are shown to sensitively detect phosphorylation of purified CaMKII. The basal phosphorylation of CaMKII from the intermediate medial hyperstriatum ventrale (IMHV) and lobus parolfactorius (LPO) regions of the chick brain is shown to be largely right hemisphere-lateralized. When chicks are subjected to a passive avoidance training experience, a specific increase in CaMKII phosphorylation is induced in the IMHV and LPO of the left hemisphere from those chicks whose memory for the training experience is successfully retrieved. While this specific increase in CaMKII phosphorylation is seen in both the left IMHV and left LPO in short-term memory, it is detectable only in the left LPO associated with long-term memory retrieval. The present results provide evidence that in vivo changes in phosphorylation of CaMKII are associated specifically with processing of distinct memory stages, which take place in specific brain regions.

Recovery of memory in chicks after disruption during learning: the reversibility of amnesia induced by protein synthesis inhibitors

Protein synthesis inhibitors given during learning are known to disrupt memory in various animal species in several models of learning. However, there are suggestions that amnesia induced by protein synthesis inhibitors is not permanent--memory can be recovered by a reminder procedure, i.e., by presenting the animal with one of the components of the external environment which was part of the learning situation. The aim of the present work was to determine the existence of the reminder phenomenon in a well-studied model of single-session training to passive avoidance in chicks. Cycloheximide and anisomycin were used to induce amnesia. Reminder was performed using the aversive taste of methylanthranilate 24 h after training, and testing was conducted 48 h after training. The results obtained provide evidence that memory disrupted by protein synthesis inhibitors in chicks can be recovered by the reminder procedure.

Protein kinase C, learning and memory: a circular determinism between physiology and behaviour

1. In vertebrates as in invertebrates, protein kinase C appears to have a key role in learning and memory, probably given its involvement in synaptic plasticity. 2. Hippocampal PKC in mammalians is activated by learning in a large variety of memory tasks. However, the kind of information processed, the type of task, and the dynamics of learning processes all induce differential changes in the mode of PKC activation and in its anatomy. 3. The behaviourally induced changes in PKC activity are often varying in their magnitude. Inter-individual differences in PKC basal activity are generally correlated to the ability to learn. 4. Pharmacologic activation and inhibition of brain PKC shows that PKC activation plays an important role in cognitive function. 5. Basal PKC stores characterising each individual could be determined by genetic factors and modulated through life by individual experience. 6. The issue of PKC and memory relationships is reformulated through a comprehensive interactionist model which leads to formulating some new testable predictions.

Aspects of the search for neural mechanisms of memory

The search for neural mechanisms of memory has been under way for more than a century. The pace quickened in the 1960s when investigators found that training or differential experience leads to significant changes in brain neurochemistry, anatomy, and electrophysiology. Many steps have now been identified in the neurochemical cascade that starts with neural stimulation and ends with encoding information in long-term memory. Applications of research in this field are being made to child development, successful aging, recovery from brain damage, and animal welfare. Extensions of current research and exciting new techniques promise novel insights into mechanisms of memory in the decades ahead.