The memory enhancing effect of the APP-derived tripeptide Ac-rER is mediated through CRMP2.

The diasteromeric (D/L) form of the acetylated tripeptide rER (NH2-D-arg-L-glu-D-arg-COOH), derived from the external domain of amyloid precursor protein, protects against amyloid-ß induced memory loss for a passive avoidance task in young chicks and enhances retention for a weak version of the task when injected peripherally up to 12 h prior to training. The tripeptide readily crosses the blood-brain barrier, binds to receptor sites in the brain and is without adverse effects on general behaviour. The mechanisms of its action are unknown, as are its target molecules/pathways. Here, we report the binding partners for Ac-rER are collapsin response mediator protein 2 (CRMP2), syntaxin binding protein 1 and heat shock protein 70. Behavioural studies of the effects of Ac-rER on memory retention confirmed that the effect of Ac-rER is mediated via CRMP2, as anti-CRMP2 antibodies if injected intracranially 30 min pre-training, induced amnesia for the passive avoidance task. However, Ac-rER, if injected prior to the anti-CRMP2, rescues the memory deficits induced by anti-CRMP2 antibodies. As CRMP2 is placed at the junction of many different cellular processes during brain development and in adult neuronal plasticity as well as being implicated in Alzheimer's disease, this strengthens the claim that Ac-rER may be a potential therapeutic agent in Alzheimer's disease, although its precise mode of action remains to be elucidated.

Protection against Abeta-induced memory loss by tripeptide D-Arg-L-Glu-L-Arg.

The molecular and cellular mechanisms underlying the memory deficits in Alzheimer's disease are increasingly thought to be associated with faulty processing of amyloid precursor protein. Following our earlier findings that it is possible to use the tripeptide RER (NH2-D-Arg-L-Glu-L-Arg-COOH, derived from the external domain of amyloid precursor protein) to rescue memory in animal models, we report here that the diasteromeric (D/L) form of the acetylated tripeptide RER protects against Abeta-induced memory loss for a passive avoidance task in young chicks and enhances retention for a weak version of the task when injected peripherally up to 12 h before training. The tripeptide readily crosses the blood-brain barrier, binds to membrane receptor sites in the brain and is without adverse effects on general behaviour. We discuss this finding in the context of other studies of the importance of peptides containing D-amino acids, and conclude that these RER-related peptides may form the basis for a potential therapeutic agent in the early stages of Alzheimer's disease.

Recalling an aversive experience by day-old chicks is not dependent on somatic protein synthesis.

Long-term memory is dependent on protein synthesis and inhibiting such synthesis following training results in amnesia for the task. Proteins synthesized during training must be transported to the synapse and disrupting microtubules with Colchicines, and hence, blocking transport, results in transient amnesia. Reactivating memory for a previously learned avoidance triggers a biochemical cascade analogous to that following the initial training and renders the memory labile once more to protein synthesis inhibitors. However, the reminder-induced cascade differs in certain key features from that following training. Here we show that in a one-trial passive avoidance task in chicks, in contrast with initial consolidation following training, memory following a reminder is not impaired by Colchicine. We conclude that recall after a reminder does not require synaptic access to somatically synthesized proteins in this task. Our results support the hypothesis that in the chick, a reminder may instead engage local protein synthesis at the synapse, rather than in the soma.

Glycan analysis of the chicken synaptic plasma membrane glycoproteins--a major synaptic N-glycan carries the LewisX determinant.

The majority of synaptic plasma membrane components are glycosylated. It is now widely accepted that this post-translational modification is crucial during the establishment, maintenance and function of the nervous system. Despite its significance, structural information about the glycosylation of nervous system specific glycoproteins is very limited. In the present study the major glycan structures of the chicken synaptic plasma membrane (SPM) associated glycoprotein glycans were determined. N-glycans were released by hydrazinolysis, labelled with 2-aminobenzamide, treated with neuraminidase and subsequently fractionated by size exclusion chromatography. Individual fractions were characterized by the combination of high-pressure liquid chromatography, exoglycosidase treatment or reagent array analysis method (RAAM). In addition to oligomannose-type glycans, core-fucosylated complex glycans with biantennary bisecting glycans carrying the LewisX epitope were most abundant. The overall chicken glycan profile was strikingly similar to the rat brain glycan profile. The presence of the LewisX determinant in relatively large proportions suggests a tissue-specific function for these glycans.

Amyloid precursor protein: from synaptic plasticity to Alzheimer's disease.

The amyloid precursor protein (APP) has been shown to be implicated in age-associated plastic changes at synapses that might contribute to memory loss in Alzheimer's disease. As APP has previously been reported to have multiple functions during normal development, and as human and avian APP share 95% homology in amino acid sequence, we have employed a one-trial passive avoidance task in day-old chicks to study its role in the process of memory formation. Administration of anti-APP antibodies, raised against human APP, APP-antisense, and Abeta during pre-training, prevented memory formation without effects on general behavior or initial acquisition. Amnesia is apparent by 30 min post-training and lasts for at least 24 hours. Injection of APP-derived peptides RERMS (APP(328-332)) and RER (APP(328-330)) homologous to the short stretches of amino acids in the Kang sequence (APP(319-335)), rescue the memory in animals rendered amnestic by previous (anti-APP antibody, antisense, and Abeta pretreatments. The protected form of RER, with a prolonged half-life (acetylated RER), proved to be effective when injected intracranially and peripherally. The tripeptide RER exerts its biological activity by binding to two neuronal plasma membrane proteins (60 and 110 kDa). The results obtained in this study suggest that RER alleviates memory deficits via receptor-mediated events, and that short APP-derived peptides might represent a novel group of therapeutically active molecules for the alleviation of memory deficits in age-related dementias.

Sex differences in pregnenolone sulphate in the chick brain after training.

Pregnenolone and pregnenolone sulphate are potent memory enhancers when administered to rodents prior to various learning and memory paradigms. Here, we show that training on a passive avoidance task results in the increased concentration of pregnenolone sulphate in the medial striatum, formerly known as lobus parolfactorius of female but not male chicks. In addition, we demonstrated potential for neuronal synthesis of pregnenolone in the day-old chick brain, including in the intermediate medial mesopallium, formerly known as intermediate medial hyperstriatum ventrale and the medial striatum.

The distributed neuronal systems supporting choice-making in real-life situations: differences between men and women when choosing groceries detected using magnetoencephalography.

In this work, magnetoencephalography was used to study the temporal dynamics of neural responses in 16 subjects (eight women, eight men) choosing among different day-to-day consumer items. At short latencies (< 150 ms), the evoked responses showed striate and extrastriate cortical activation common to the processing of general objects. At about 300 ms, women activated preferentially left posterior cortices, whereas men activated preferentially right temporal cortices. This may reflect sex/gender differences in cognitive strategies, emphasizing category-specific knowledge in women and spatial memories in men. At latencies greater than 500 ms, right parietal cortices were preferentially activated when previously bought or used items were chosen. In contrast, left inferior and right orbital cortices were preferentially activated when selecting less-known items. This may be interpreted as representing the neural correlates of decisions where the outcome is consistent with previous experience, and of choices which are 'difficult' in some sense. Analysis of coherent gamma-oscillations (20-45 Hz) revealed neural activity over left anterior and right dorsolateral cortices at long latency (> 1500 ms) when brand knowledge is low. This is consistent with the late binding of (brand) memories and evaluation of multiple sources of information when a choice is not obvious. gamma-Activity showed that women may activate larger neural networks when preference is high, suggesting that men and women exhibit different patterns of neural activity even though their overt performances are similar.

Reminder effects: the molecular cascade following a reminder in young chicks does not recapitulate that following training on a passive avoidance task.

Memory traces, once established, are no longer sensitive to disruption by metabolic inhibitors. However, memories reactivated by reminder are once again vulnerable, in a time-dependent manner, to amnestic treatment. To determine whether the metabolic events following a reminder recapitulate those following initial training we examined the temporal dynamics of amnesia induced by the protein synthesis inhibitor anisomycin and the glycosylation inhibitor 2-deoxygalactose. The effects of both were transient and dependent on time of reminder post-training and time of injection relative to reminder, and differed from those following initial training. 2-[(14)C]-deoxyglucose uptake increased in two brain regions, the intermediate medial hyperstriatum ventrale (IMHV) and lobus parolfactorius (LPO) following reminder as it did following training, but the increase was bilateral rather than confined to the left hemisphere and was more marked in LPO than IMHV. C-fos expression after reminder was increased only in the LPO, the chick brain region associated with a late phase of memory processing and recall. Thus although, like initial consolidation, memory processing after reminder is sensitive to inhibitors of protein synthesis and glycosylation, the temporal and pharmacological dynamics indicate differences between these two processes.

Memory beyond the synapse.

Based on studies of the molecular and cellular cascades that occur during memory consolidation for a one-trial passive-avoidance learning task in the young chick, I review the evidence that memory is encoded in permanent changes in synaptic connectivity ina specific brain region, the Hebb hypothesis. I conclude that despite the fact that such a cascade occurs, culminating in the synthesis of cell-adhesion molecules that are involved in synaptic remodelling, synaptic events are not in themselves sufficient to account for the phenomena of memory. Both whole brain (neuromodulator) and whole body (hormonal) processes are engaged.Memories are labile, disarticulated and stored in a distributed manner; how the mind/brain recreates coherent memories from this pattern is a mystery.

Reminder effects - reconsolidation or retrieval deficit? Pharmacological dissection with protein synthesis inhibitors following reminder for a passive-avoidance task in young chicks.

It is generally accepted that memory formation involves an irreversible passage via labile phases to the stable form of 'long-term memory' impervious to amnestic agents such as protein synthesis inhibitors. However, recent experiments demonstrate that reactivation of memory by way of a reminder renders it labile to such inhibitors, suggesting that such retrieval is followed by a so-called reconsolidation process similar or identical in its cellular and molecular correlates to that occurring during the initial consolidation. We compared the effects of the protein synthesis inhibitor anisomycin and the glycoprotein synthesis inhibitor 2-deoxygalactose on the temporal dynamics and pharmacological sensitivity of initial consolidation and memory expression following a reminder in a one-trial passive-avoidance task in day-old chicks. This comparison revealed three differences between the action of the inhibitors on newly formed compared with reactivated memory. First, the recall deficit after the reminder was temporary, whilst the amnesia following inhibitor treatment during training was stable. Second, the sensitive period for the effect of anisomycin was shorter in the reminder than in the training situation. Third, the effective dose for either inhibitor for reminder-associated amnesia was several times lower than for amnesia developing after training. Thus though like initial consolidation, memory expression at delayed periods following reminder depends on protein and glycoprotein synthesis, the differences between the temporal and pharmacological dynamics in the two situations point to the distinct character of the molecular processes involved in postreminder effects.

Amino acid release from the intermediate medial hyperstriatum ventrale (IMHV) of day-old chicks following a one-trial passive avoidance task.

Indirect evidence has implicated glutamate and gamma-amino butyric acid in memory formation for one-trial passive avoidance learning. We have further examined this by following the time course of glutamate and gamma-amino butyric acid release from slices prepared from the intermediate medial hyperstriatum ventrale of day-old chicks (Ross 1 Chunky) trained to avoid a bead covered in the aversant methylanthranilate. At various times after training, slices of left and right intermediate medial hyperstriatum ventrale were incubated in medium containing 50 mM potassium chloride and amino acid release was determined. Thirty minutes after training there was a bilateral increase in calcium-dependent glutamate release in slices from methylanthranilate-trained chicks compared to those trained to peck water. This increase was sustained until 1 h in the left hyperstriatum when an increase in calcium-dependent gamma-amino butyric acid release was also apparent. Glutamate uptake was also enhanced in left hyperstriatum (30 and 60 min) and in the right at 30 min. In the right intermediate medial hyperstriatum ventrale of methylanthranilate birds glutamate release was increased from 3 to 6.5 h and gamma-amino butyric acid at 6.5 h: a time that corresponded to the mobilization of a late process required if long-term memory was to be formed. These results confirm that the amino acids glutamate and gamma-amino butyric acid are released from the intermediate hyperstriatum ventrale in a calcium-dependent, neurotransmitter-like manner. Furthermore, changes in the release of these two amino acids accompany memory formation for a one-trial learning task in the day-old chick.

Memory Formation in Day-old Chicks Requires NMDA but not Non-NMDA Glutamate Receptors.

The non-competitive N-methyl-d-aspartate (NMDA) antagonist MK-801, injected intraperitoneally at 0.1 mg/kg, at times between 1 h before and 5 min after training chicks on a one-trial passive avoidance task, resulted in amnesia for the task on test 3 or 24 h subsequently. No amnesia was apparent at 24 h if chicks were injected between 1 and 6 h after training. Amnesia did not develop immediately; it was not apparent 30 min after training in chicks injected 5 min after training. At this dose of MK-801 no other effects on motor or pecking behaviour of the birds were observed. Bilateral or unilateral intracerebral injections of 1.5 nM MK-801 5 min after training produced a similar amnesia at 3 h to that of intraperitoneally injected MK-801; no hemispheric differences were observed, presumably because of the ready diffusion of the MK-801. By contrast, intracerebral injections of the non-NMDA glutamate antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), 6,7-dinitroquinoxaline-2,3-dione (DNQX) and 6,7-nitro-7-sulphamoyl-benzoquinoxaline-2,3-dione (NBQX) (0.066 microM) 5 min after training, despite producing severe if transient behavioural disturbances, were without effect on retention for the avoidance response in chicks tested 3 h subsequently. We interpret these results as pointing to a requirement for NMDA, but not kainate or quisqualate, receptor activation as an early enabling event in the biochemical cascade required for long-term memory formation for passive avoidance in the chick.

Learning-induced Increase of Immediate Early Gene Messenger RNA in the Chick Forebrain.

The immediate early genes c-fos and c-jun are activated rapidly in nerve cells in response to in vivo and in vitro stimulation. Because of their involvement in transcriptional regulation, the products of these genes have been proposed as nuclear signals for consolidation of long-term memory. However, no specific changes of immediate early gene expression in relation to learning have yet been reported. Compared with quiet controls, training young chicks to discriminate food grains from inedible pebbles results in a 4.8-fold elevation of c-fos and a 3.7-fold elevation of c-jun mRNA in the forebrain 30 min after an 8-min training session. Compared to chicks that had learned the discrimination and were merely repeating already learned behaviour, the increase in c-jun mRNA in the learning group was 64% (P < 0.03) but a 24% increase in c-fos mRNA was not significant. Because the increased expression is higher in birds that are learning the task than in those that are repeating already learned behaviour, and is not proportional to behavioural activity per se, we conclude that learning a new task is itself responsible for enhanced expression of the genes.

Glycoprotein Synthesis Is Necessary for Memory of Sickness-Induced Learning in Chicks.

Can current biochemical models of memory account for sickness-induced learning? We show that chicks can form an association between pecking a coloured but tasteless lure and becoming ill (LiCl, i.p.) 30 min later. We go on to demonstrate amnesia for this association, induced by intracranial administration of 2-deoxygalactose (10 micromole per hemisphere, in a 10 microl vol), an inhibitor of the synthesis of glycoproteins of the synaptic membrane, 10 min before pecking. Further, we show that this 2-deoxygalactose-induced amnesia is not state dependent. Thus the brain representation of the lure must be held, and require macromolecular syntheses, similar to those found in other forms of learning, for a considerable time before it can be associated with new significant experience. This is incompatible with contiguous synaptic firing views of memory.