Cell-adhesion molecules, glucocorticoids and long-term-memory formation

Glutamate transporter activator LDN-212320 prevents chronic pain-induced cognitive impairment and anxiety-like behaviors in a mouse model

The astroglial glutamate transporter in the hippocampus and anterior cingulate cortex (ACC) is critically involved in chronic pain-induced cognitive and psychiatric abnormalities. We have previously reported that LDN-212320, a glutamate transporter-1 (GLT-1) activator, attenuates complete Freund's adjuvant (CFA)-induced acute and chronic nociceptive pain. However, the cellular and molecular mechanisms underlying GLT-1 modulation in the hippocampus and ACC during chronic pain-induced cognitive deficit-like and anxiety-like behaviors remain unknown. Here, we have investigated the effects of LDN-212320 on CFA-induced chronic pain associated with cognitive deficit-like and anxiety-like behaviors in mice. We have evaluated the effects of LDN-212320 on CFA-induced impaired spatial, working, and recognition memory using Y-maze and object-place recognition tests. In addition, we have determined the effects of LDN-21230 on chronic pain-induced anxiety-like behaviors using elevated plus maze and marble burying test. We have also examined the effects of LDN-212320 on cAMP response element-binding protein (pCREB), brain-derived neurotrophic factor (BDNF), protein kinase A (PKA), and Ca2 +/calmodulin-dependent protein kinase II (CaMKII) expression in the hippocampus and ACC during CFA-induced cognitive deficit-like and anxiety-like behaviors using the Western blot analysis and immunofluorescence assay. Pretreatment with LDN-212320 (20 mg/kg) significantly attenuated CFA-induced impaired spatial, working, and recognition memory. Furthermore, LDN-212320 (20 mg/kg) significantly reduced CFA-induced anxiety-like behaviors. Additionally, LDN-212320 (20 mg/kg) significantly reversed CFA-induced decreased pCREB, BDNF, PKA and CaMKII expression in the hippocampus and ACC. Overall, these results suggest that the LDN-212320 prevents CFA-induced cognitive deficit-like and anxiety-like behaviors by activating CaMKII/CREB/BDNF signaling pathway in the hippocampus and ACC. Therefore, LDN-212320 could be a potential treatment for chronic pain associated with cognitive impairment and anxiety-like behaviors.

Evolutionary conserved role of neural cell adhesion molecule-1 in memory

The neural cell adhesion molecule 1 (NCAM-1) has been implicated in several brain-related biological processes, including neuronal migration, axonal branching, fasciculation, and synaptogenesis, with a pivotal role in synaptic plasticity. Here, we investigated the evolutionary conserved role of NCAM-1 in learning and memory. First, we investigated sustained changes in ncam-1 expression following aversive olfactory conditioning in C. elegans using molecular genetic methods. Furthermore, we examined the link between epigenetic signatures of the NCAM1 gene and memory in two human samples of healthy individuals (N = 568 and N = 319) and in two samples of traumatized individuals (N = 350 and N = 463). We found that olfactory conditioning in C. elegans induced ncam-1 expression and that loss of ncam-1 function selectively impaired associative long-term memory, without causing acquisition, sensory, or short-term memory deficits. Reintroduction of the C. elegans or human NCAM1 fully rescued memory impairment, suggesting a conserved role of NCAM1 for memory. In parallel, DNA methylation of the NCAM1 promoter in two independent healthy Swiss cohorts was associated with memory performance. In two independent Sub-Saharan populations of conflict zone survivors who had faced severe trauma, DNA methylation at an alternative promoter of the NCAM1 gene was associated with traumatic memories. Our results support a role of NCAM1 in associative memory in nematodes and humans, and might, ultimately, be helpful in elucidating diagnostic markers or suggest novel therapy targets for memory-related disorders, like PTSD.

Glycans and glycosaminoglycans in neurobiology: key regulators of neuronal cell function and fate

The aim of the present study was to examine the roles of l-fucose and the glycosaminoglycans (GAGs) keratan sulfate (KS) and chondroitin sulfate/dermatan sulfate (CS/DS) with selected functional molecules in neural tissues. Cell surface glycans and GAGs have evolved over millions of years to become cellular mediators which regulate fundamental aspects of cellular survival. The glycocalyx, which surrounds all cells, actuates responses to growth factors, cytokines and morphogens at the cellular boundary, silencing or activating downstream signaling pathways and gene expression. In this review, we have focused on interactions mediated by l-fucose, KS and CS/DS in the central and peripheral nervous systems. Fucose makes critical contributions in the area of molecular recognition and information transfer in the blood group substances, cytotoxic immunoglobulins, cell fate-mediated Notch-1 interactions, regulation of selectin-mediated neutrophil extravasation in innate immunity and CD-34-mediated new blood vessel development, and the targeting of neuroprogenitor cells to damaged neural tissue. Fucosylated glycoproteins regulate delivery of synaptic neurotransmitters and neural function. Neural KS proteoglycans (PGs) were examined in terms of cellular regulation and their interactive properties with neuroregulatory molecules. The paradoxical properties of CS/DS isomers decorating matrix and transmembrane PGs and the positive and negative regulatory cues they provide to neurons are also discussed.

HNK-1 Carrier Glycoproteins Are Decreased in the Alzheimer's Disease Brain

The human natural killer-1 (HNK-1), 3-sulfonated glucuronic acid, is a glycoepitope marker of cell adhesion that participates in cell-cell and cell-extracellular matrix interactions and in neurite growth. Very little is known about the regulation of the HNK-1 glycan in neurodegenerative disease, particularly in Alzheimer's disease (AD). In this study, we investigate changes in the levels of HNK-1 carrier glycoproteins in AD. We demonstrate an overall decrease in HNK-1 immunoreactivity in glycoproteins extracted from the frontal cortex of AD subjects, compared with levels from non-demented controls (NDC). Immunoblotting of ventricular post-mortem and lumbar ante-mortem cerebrospinal fluid with HNK-1 antibodies indicate similar levels of carrier glycoproteins in AD and NDC samples. Decrease in HNK-1 carrier glycoproteins were not paralleled by changes in messenger RNA (mRNA) levels of the enzymes involved in the synthesis of the glycoepitope, β-1,4-galactosyltransferase (β4GalT), glucuronyltransferases GlcAT-P and GlcAT-S, or sulfotransferase HNK-1ST. Over-expression of amyloid precursor protein in Tg2576 transgenic mice and in vitro treatment of SH-SY5Y neuroblastoma cells with the amyloidogenic Aβ42 peptide resulted in a decrease in HNK-1 immunoreactivity levels in brain and cellular extracts, whereas the levels of soluble HNK-1 glycoproteins detected in culture media were not affected by Aβ treatment. HNK-1 levels remain unaffected in the brain extracts of Tg-VLW mice, a model of mutant hyperphosphorylated tau, and in SH-SY5Y cells over-expressing hyperphosphorylated wild-type tau. These results provide evidence that cellular levels of HNK-1 carrier glycoforms are decreased in the brain of AD subjects, probably influenced by the β-amyloid protein.

Cocaine and MDMA Induce Cellular and Molecular Changes in Adult Neurogenic Systems: Functional Implications

The capacity of the brain to generate new adult neurons is a recent discovery that challenges the old theory of an immutable adult brain. A new and fascinating field of research now focuses on this regenerative process. The two brain systems that constantly produce new adult neurons, known as the adult neurogenic systems, are the dentate gyrus (DG) of the hippocampus and the lateral ventricules/olfactory bulb system. Both systems are involved in memory and learning processes. Different drugs of abuse, such as cocaine and MDMA, have been shown to produce cellular and molecular changes that affect adult neurogenesis. This review summarizes the effects that these drugs have on the adult neurogenic systems. The functional relevance of adult neurogenesis is obscured by the functions of the systems that integrate adult neurons. Therefore, we explore the effects that cocaine and MDMA produce not only on adult neurogenesis, but also on the DG and olfactory bulbs. Finally, we discuss the possible role of new adult neurons in cocaine- and MDMA-induced impairments. We conclude that, although harmful drug effects are produced at multiple physiological and anatomical levels, the specific consequences of reduced hippocampus neurogenesis are unclear and require further exploration.

The septic brain

Sepsis is a major disease entity with important clinical implications. Sepsis-induced multiple organ failure is associated with a high mortality rate in humans and is clinically characterized by pulmonary, cardiovascular, renal and gastrointestinal dysfunction. Recently, several studies have demonstrated that sepsis survivors present long-term cognitive impairment, including alterations in memory, attention, concentration and/or global loss of cognitive function. However, the pathogenesis and natural history of septic encephalopathy and cognitive impairment are still poorly known and further understanding of these processes is necessary for the development of effective preventive and therapeutic interventions. This review discusses the clinical presentation and underlying pathophysiology of the encephalopathy and cognitive impairment associated with sepsis.

Neuro-economics in chicks: foraging choices based on amount, delay and cost

Studies on the foraging choices are reviewed, with an emphasis on the neural representations of elementary factors of food (i.e., amount, delay and consumption time) in the avian brain. Domestic chicks serve as an ideal animal model in this respect, as they quickly associate cue colors with subsequently supplied food rewards, and their choices are quantitatively linked with the rewards. When a pair of such color cues was simultaneously presented, the trained chicks reliably made choices according to the profitability of food associated with each color. Two forebrain regions are involved in distinct aspects of choices; i.e., nucleus accumbens-medial striatum (Ac-MSt) and arcopallium intermedium (AI), an association area in the lateral forebrain. Localized lesions of Ac-MSt enhanced delay aversion, and the ablated chicks made impulsive choices of immediate reward more frequently than sham controls. On the other hand, lesions of AI enhanced consumption-time aversion, and the ablated chicks shifted their choices toward easily consumable reward with their impulsiveness unchanged; delay and consumption time are thus doubly dissociated. Furthermore, chicks showed distinct patterns of risk-sensitive choices depending on the factor that varied at trials. Risk aversion occurred when food amount varied, whereas consistent risk sensitivity was not found when the delay varied; amount and delay were not interchangeable. Choices are thus deviated from those predicted as optima. Instead, factors such as amount, delay and consumption time could be separately represented and processed to yield economically sub-optimal choices.

The evidence for hippocampal long-term potentiation as a basis of memory for simple tasks

Long-term potentiation (LTP) is the enhancement of postsynaptic responses for hours, days or weeks following the brief repetitive afferent stimulation of presynaptic afferents. It has been proposed many times over the last 30 years to be the basis of long-term memory. Several recent findings finally supported this hypothesis: a) memory formation of one-trial avoidance learning depends on a series of molecular steps in the CA1 region of the hippocampus almost identical to those of LTP in the same region; b)hippocampal LTP in this region accompanies memory formation of that task and of another similar task. However, CA1 LTP and the accompanying memory processes can be dissociated, and in addition plastic events in several other brain regions(amygdala, entorhinal cortex, parietal cortex) are also necessary for memory formation of the one-trial task, and perhaps of many others.

Acute amphetamine treatment decreases the expression of 180–200 kDa isoform of polysialic acid linked neural cell adhesion molecule in mouse hippocampus

The behavioral sensitization produced by repeated treatment with amphetamine may represent neural adaptations underlying some of the features of psychosis and addiction in humans. Under some circumstances, learning contextual cues can gain powerful control over the ability of the sensitized neural substrate to influence behavior. Here, we investigated the expression levels of a neural cell adhesion molecule (NCAM) and a polysialylated form of the neuronal cell adhesion molecule (PSA-NCAM) as markers of synaptic plasticity, in the associative learning mechanisms related to behavioral sensitization. To achieve our goal we examined the effects of amphetamine treatment on the expression levels of PSA-NCAM and NCAM in mouse hippocampus, cortex and striatum in a context-specific behavioral sensitization model. We found that amphetamine (2.0 mg/kg, i.p.) produced robust behavioral sensitization and the expression of sensitization after the saline challenge was context-dependent. Immunoblotting analysis demonstrated that acute administration of amphetamine selectively and time-dependently decreases the expression of 180-200 kDa isoform of PSA-NCAM in hippocampus in both context associated (the Paired) as well as context non-associated (the Unpaired) groups. Thus, our results suggest that acute amphetamine administration time-dependently decreases the expression of 180-200 kDa isoform of PSA-NCAM in mouse hippocampus and PSA-NCAM is not involved in amphetamine-induced associated learning mechanism.

From Malthus to motive: how the HPA axis engineers the phenotype, yoking needs to wants

The hypothalamo-pituitary-adrenal (HPA) axis is the critical mediator of the vertebrate stress response system, responding to environmental stressors by maintaining internal homeostasis and coupling the needs of the body to the wants of the mind. The HPA axis has numerous complex drivers and highly flexible operating characterisitics. Major drivers include two circadian drivers, two extra-hypothalamic networks controlling top-down (psychogenic) and bottom-up (systemic) threats, and two intra-hypothalamic networks coordinating behavioral, autonomic, and neuroendocrine outflows. These various networks jointly and flexibly control HPA axis output of periodic (oscillatory) functions and a range of adventitious systemic or psychological threats, including predictable daily cycles of energy flow, actual metabolic deficits over many time scales, predicted metabolic deficits, and the state-dependent management of post-prandial responses to feeding. Evidence is provided that reparation of metabolic derangement by either food or glucocorticoids results in a metabolic signal that inhibits HPA activity. In short, the HPA axis is intimately involved in managing and remodeling peripheral energy fluxes, which appear to provide an unidentified metabolic inhibitory feedback signal to the HPA axis via glucocorticoids. In a complementary and perhaps a less appreciated role, adrenocortical hormones also act on brain to provide not only feedback, but feedforward control over the HPA axis itself and its various drivers, as well as coordinating behavioral and autonomic outflows, and mounting central incentive and memorial networks that are adaptive in both appetitive and aversive motivational modes. By centrally remodeling the phenotype, the HPA axis provides ballistic and predictive control over motor outflows relevant to the type of stressor. Evidence is examined concerning the global hypothesis that the HPA axis comprehensively induces integrative phenotypic plasticity, thus remodeling the body and its governor, the brain, to yoke the needs of the body to the wants of the mind. Adverse side effects of this yoking under conditions of glucocorticoid excess are discussed.

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.

Post-training intrahippocampal injection of synthetic poly-alpha-2,8-sialic acid-neural cell adhesion molecule mimetic peptide improves spatial long-term performance in mice

Several data have shown that the neural cell adhesion molecule (NCAM) is necessary for long-term memory formation and might play a role in the structural reorganization of synapses. The NCAM, encoded by a single gene, is represented by several isoforms that differ with regard to their content of alpha-2,8-linked sialic acid residues (PSA) on their extracellular domain. The carbohydrate PSA is known to promote plasticity, and PSA-NCAM isoforms remain expressed in the CA3 region of the adult hippocampus. In the present study, we investigated the effect on spatial memory consolidation of a PSA gain of function by injecting a PSA mimetic peptide (termed pr2) into the dorsal hippocampus. Mice were subjected to massed training in the spatial version of the water maze. Five hours after the last training session, experimental mice received an injection of pr2, whereas control mice received PBS or reverse peptide injections in the hippocampal CA3 region. Memory retention was tested at different time intervals: 24 h, 1 wk, and 4 wk. The results showed that the post-training infusion of pr2 peptide significantly increases spatial performance whenever it was assessed after the training phase. By contrast, administration of the control reverse peptide did not affect retention performance. These findings provide evidence that (1) PSA-NCAM is involved in memory consolidation processes in the CA3 hippocampal region, and (2) PSA mimetic peptides can facilitate the formation of long-term spatial memory when injected during the memory consolidation phase.

Passive avoidance training decreases synapse density in the hippocampus of the domestic chick

The bird hippocampus (Hp), although lacking the cellular lamination of the mammalian Hp, possesses comparable roles in spatial orientation and is implicated in passive avoidance learning. As in rodents it can be divided into dorsal and ventral regions based on immunocytochemical, tracing and electrophysiological studies. To study the effects of passive avoidance learning on synapse morphometry in the Hp, spine and shaft synapse densities of 1-day-old domestic chicks were determined in dorsal and ventral Hp of each hemisphere by electron microscopy, 6 and 24 h following training to avoid pecking at a bead coated with a bitter-tasting substance, methyl anthranilate (MeA). The density of asymmetric spine and shaft synapses in MeA-trained birds at 6 h post-training was significantly lower in the dorsal and ventral Hp of the right hemisphere relative to control (untrained) chicks, but by 24 h this difference was absent. A hemispheric asymmetry was apparent in the ventral Hp where the water-trained group showed enhanced shaft and spine synapse density in the left hemisphere, whilst in the MeA-trained group only asymmetric shaft synapses follow the same pattern in relation to the right hemisphere. There were no differences in asymmetric shaft synapses in the dorsal Hp at 6 h post-training, but at 24 h post-training there was a reduction in the density of shaft synapses in the right hemisphere in MeA compared with control birds. These data are discussed in relation to the pruning effects of stress and learning on synapse density in chick Hp.

Localized lesions of ventral striatum, but not arcopallium, enhanced impulsiveness in choices based on anticipated spatial proximity of food rewards in domestic chicks

The effects of bilateral chemical lesions of the ventral striatum (nucleus accumbens and the surrounding areas in the medial striatum) and arcopallium (major descending area of the avian telencephalon) were examined in 1-2-weeks old domestic chicks. Using a Y-maze, we analyzed the lesion effects on the choices that subject chicks made in two tasks with identical economical consequences, i.e., a small-and-close food reward vs. a large-and-distant food reward. In task 1, red, yellow, and green beads were associated with a feeder placed at various distances from the chicks; chicks thus anticipated the spatial proximity of food by the bead's color, whereas the quantity of the food was fixed. In task 2, red and yellow flags on the feeders were associated with various amount of food; the chicks thus anticipated the quantity of food by the flag's color, whereas the proximity of the reward could be directly visually determined. In task 1, bilateral lesions of the ventral striatum (but not the arcopallium) enhanced the impulsiveness of the chicks' choices, suggesting that choices based on the anticipated proximity were selectively changed. In task 2, similar lesions of the ventral striatum did not change choices. In both experiments, motor functions of the chicks remained unchanged, suggesting that the lesions did not affect the foraging efficiency, i.e., objective values of food. Neural correlates of anticipated food rewards in the ventral striatum (but not those in the arcopallium) could allow chicks to invest appropriate amount of work-cost in approaching distant food resources.

Social recognition memory requires two stages of protein synthesis in mice

Olfactory recognition memory was tested in adult male mice using a social discrimination task. The testing was conducted to begin to characterize the role of protein synthesis and the specific brain regions associated with activity in this task. Long-term olfactory recognition memory was blocked when the protein synthesis inhibitor anisomycin was injected 20 min before, immediately after, or 6 h after sampling. No effect was observed when anisomycin was administered 3 h or 18 h after sampling. Immunohistochemical analysis of Fos expression revealed that sampling-like exposure to a juvenile increased the activity of a subset of cells in the accessory olfactory bulb and the brain areas that are associated with it. Additionally, increased Fos expression was measured in the main olfactory bulb and the piriform cortex, whereas no signs of activation were seen in the cortical nucleus of the amygdala, all components of the main olfactory system. No increases in Fos immunoreactivity were observed after 4 h. Our data suggest that long-lasting olfactory recognition memory requires two stages of protein synthesis. The first stage takes place within 1-2 h and the second stage between 6-7 h after sampling. The first but not the second stage is paralleled by an increase in the number of Fos-immunoreactive cells in brain areas associated with both the main and accessory olfactory systems. It therefore appears that the role of the second stage of protein synthesis in recognition memory depends on the integrity of the first stage of protein synthesis.

Acute and repeated administration of cocaine differentially regulates expression of PSA-NCAM-positive neurons in the rat hippocampus

Recent data indicating that addictive substances are able to alter brain plasticity and its morphology inclined us to determine whether acute and chronic cocaine administration could modify the expression of a polysialylated form of the neuronal cell adhesion molecule (PSA-NCAM) in the dentate gyrus of the rat hippocampus. Alterations in the PSA-NCAM expression are known to effect a variety of neuroanatomical rearrangements in the brain structure. Cocaine was administered acutely (15 mg/kg, i.p.) or repeatedly (15 mg/kg, i.p. once a day for five consecutive days). The number of PSA-NCAM immunopositive cells was determined at six time points after cocaine treatment: 6 h and 1, 2, 4, 6, and 10 days (both in acute and repeated treatment). It was found that a single injection of cocaine induced a time-dependent decrease in the number of PSA-NCAM cells in the dentate gyrus. The decrease was observed on day 1 after cocaine treatment and lasted for at least 6 days. In contrast, an increase in the number of PSA-NCAM-positive cells in the dentate gyrus was observed 2 and 4 days after the last dose of repeated cocaine. It is concluded that cocaine can evoke long-lasting changes in the PSA-NCAM protein expression in the dentate gyrus and that the direction of cocaine-induced PSA-NCAM changes depends on the regimen of cocaine administration. It is postulated that cocaine may have impact on hippocampal plasticity and subsequent processes that are controlled by plastic changes in the hippocampal structure.

Memory functions in prednisone-treated kidney transplant patients

The literature indicates that high daily doses of gluco-corticosteroids have a degenerating effect upon the hippocampus and thus result in reduced declarative memory capacities. In order to prevent rejection, renal transplant recipients are treated with moderate daily doses of gluco-corticosteroids and, if necessary, with high pulse-doses during a few days. The question, therefore, arises as to whether or not such standard treatments result in memory impairments. For this reason, declarative memory capacities were measured, by means of a Dutch version of Rey's 15 Words Test, in a group of 52 renal transplant recipients. Results clearly indicated severe reductions in declarative memory capacities in these patients.

Learning twice is different from learning once and from learning more

The rat hippocampus plays a crucial role in the consolidation of a variety of memories, including that for a one trial inhibitory avoidance learning task in which stepping down from a platform is associated with a footshock. Here we show that this is the case regardless of the intensity of the footshock used and hence, of the strength of the learned response. However, additional learning produced by a second training session in this task does not involve the hippocampus but, instead, the striatum. Memory consolidation of the second trial requires glutamate alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate, N-methyl-D-aspartate and metabotropic receptors, activation of signaling pathways, gene expression and protein synthesis in the striatum, as are required in the hippocampus during memory consolidation of the first trial.

Dynamics of olfactory learning-induced up-regulation of L1 in the piriform cortex and hippocampus

L1 is a cell adhesion molecule implicated in the formation of neural circuits and synaptic plasticity. We have examined the sequence and time-frame in which modifications in the synaptic expression of L1 occur in the piriform cortex and hippocampus in the course of rule learning of an olfactory discrimination task. Rats were trained to choose the correct odour in a pair to be rewarded with drinking water. Such training requires 6-8 days on average before rats reach maximal performance. We observed a learning-induced L1 up-regulation that occurred at an early training stage in the piriform cortex but only after rule-learning establishment in the hippocampus. We suggest that the dynamics of L1 up-regulation may reflect the functional role of these brain regions in olfactory rule learning.

Pretraining but not Preexposure to the Task Apparatus Prevents the Memory Impairment Induced by Blockade of Protein Synthesis, PKA or MAP Kinase in Rats

Adult male Wistar rats were trained and tested in a step-down inhibitory avoidance task (0.4 mA footshock, 24 h training-test interval). Fifteen minutes before or 0, 1.5 or 3 hours after training, animals received a 0.8 microl intrahippocampal infusion of the protein synthesis inhibitor anisomycin (80 microg), the PKA inhibitor Rp-cAMP (0.05 microg), the MAPK kinase inhibitor PD 098059 (50 microM solution) or vehicle (phosphate buffer in saline, pH 7.4). Anisomycin, Rp-cAMP and PD 098059 impaired retention test performance in animals injected at different times, prior and after training. Pretraining with a low footshock intensity (0.2 mA) 24 h before training prevented the amnestic effect of all drugs studied. However, simple preexposure to the inhibitory avoidance apparatus did not alter the amnestic effects of all drugs. The results suggest that memory processing requires hippocampal mechanisms dependent on protein synthesis, PKA and MAPK kinase at different times after training. These findings suggest that weak training must be sufficient to produce some lasting cellular expression of the experience so that the enhancement of consolidation of a previously acquired memory is not dependent on protein synthesis, PKA or MAPK.

Neural cell adhesion molecule in human serum. Increased levels in dementia of the Alzheimer type

Memory impairment is a process associated with alterations in neuronal plasticity, synapses formation, and stabilization. As the neural cell adhesion molecule (NCAM) plays a key role in synaptic bond stabilization, we analyzed the usefulness of soluble NCAM isoforms in the diagnosis of patients with dementia of the Alzheimer type (DAT). NCAM was measured in the sera of 70 control subjects and 43 DAT patients (with different severity of cognitive impairment, GDS), employing Western blot and densitometric quantification. LMW-NCAM bands (100-130 kDa) decreased significantly with age independently of sex. DAT patients presented values of LMW-NCAM and HMW-NCAM significantly higher than healthy controls of similar age (higher than 130 kDa). Only LMW-NCAM was associated with GDS. Our results suggest that NCAM could be involved in the pathogenesis of DAT disorder and that serum NCAM levels could be useful as differential diagnostic markers of the disease.

Post-training administration of a synthetic peptide ligand of the neural cell adhesion molecule, C3d, attenuates long-term expression of contextual fear conditioning

The neural cell adhesion molecule (NCAM) plays a key role in synaptic plasticity and memory formation. We have recently developed a synthetic peptide, termed C3d, which, through the binding to the first, N-terminal immunoglobulin-like (Ig) module in the extracellular portion of NCAM, has been shown to promote neurite outgrowth and synapse formation in vitro, and to interfere with passive avoidance memory in rats in vivo. In this study, we investigated whether the i.c.v. administration of C3d, either 5.5 h after or 2 days before training, could be effective to modulate the strength at which emotional memory for aversive situations is established into a long-term memory. The effects of the peptide were evaluated in adult male Wistar rats trained in the contextual fear conditioning task. The results indicated that C3d significantly reduced the subsequent long-term retention of the conditioned fear response when administered 5.5 h post-training, as indicated by retention tests performed 2-3 and 7 days post-training. However, this treatment failed to influence conditioning for this task when injected 2 days pre-training. Additional experiments showed that C3d did not influence the emotional or locomotor behaviour of the animals, when tested in the open field task. Furthermore, hippocampal levels of microtubule-associated protein 2 (MAP2), Synaptophysin and NCAM were found unchanged when evaluated by enzyme-linked immunosorbent assay in crude synaptosomal preparations 2 days after peptide i.c.v. injection. Therefore, post-training injection of this synthetic peptide was efficient to attenuate the strength at which memory for contextual fear conditioning was enduringly stored, whilst it did not affect the acquisition of new memories. In addition to further support the view that NCAM is critically involved in memory consolidation, the current findings suggest that the NCAM IgI module is a potential target for the development of therapeutic drugs capable to reduce the cognitive impact induced by exposure to intensive stress experiences.

Consolidation of memory for odour-reward association requires transient polysialylation of the neural cell adhesion molecule in the rat hippocampal dentate gyrus

Cell adhesion molecule function is involved in hippocampal synaptic plasticity and is associated with memory consolidation. At the infragranular zone of the dentate gyrus, neurons expressing the polysialylated form of the neural cell adhesion molecule (NCAM PSA) transiently increase their frequency at the 12-hr posttraining time in behaviours elicited by stressful stimuli, such as those associated with conditioned avoidance, water maze, and fear conditioning paradigms. To determine whether learning-induced modulation of NCAM polysialylation is limited to stressful paradigms, we employed a reward-based odour discrimination task. Animals show a rapid acquisition and recall of this task in terms of latency to identify the food-associated odour and the number of choice errors. Immunohistochemical procedures were employed to determine the change in NCAM PSA expression following task acquisition. NCAM PSA immunoreactivity in the hippocampal formation was most intense on the granule-like neurons in the infragranular zone of the dentate gyrus, and their frequency transiently increased in the 12-hr posttraining period. The nature of the transient increase in NCAM PSA-immunoreactive neurons was indistinguishable from that observed following avoidance conditioning or spatial learning, in that it occurred at the same time. The transient increase in NCAM PSA expression is suggested to facilitate dendritic elaboration in response to the acquisition of novel behavioural repertoires.

[Memory consolidation and posttraumatic stress disorder]

Extensive evidence from animal and human studies has shown that memory formation is enhanced by an endogenous modulatory system mediated by stress hormones and activation of the amygdala. This system is an evolutionarily adaptive method of enhancing important memories. Under emotional stress, this system is activated promoting the formation of vivid, long lasting traumatic memories, which are the hallmark of PTSD. The understanding of the mechanisms underlying memory modulation might lead to an improved ability to assess and treat PTSD.

Cell adhesion molecules: key players in memory consolidation?

Experimental evidence implies that L1 and neural cell adhesion molecule (NCAM) are involved in long-term memory formation. Changes in their expression and glycosylation appear to modify the synaptic strength underlying memory consolidation. Interference with L1 and NCAM function in a variety of learning tasks in different species severely attenuates memory consolidation, indicating their involvement in an evolutionary conserved mechanism of neural plasticity.

The mind through chick eyes: memory, cognition and anticipation

To understand the animal mind, we have to reconstruct how animals recognize the external world through their own eyes. For the reconstruction to be realistic, explanations must be made both in their proximate causes (brain mechanisms) as well as ultimate causes (evolutionary backgrounds). Here, we review recent advances in the behavioral, psychological, and system-neuroscience studies accomplished using the domestic chick as subjects. Diverse behavioral paradigms are compared (such as filial imprinting, sexual imprinting, one-trial passive avoidance learning, and reinforcement operant conditioning) in their behavioral characterizations (development, sensory and motor aspects of functions, fitness gains) and relevant brain mechanisms. We will stress that common brain regions are shared by these distinct paradigms, particularly those in the ventral telencephalic structures such as AIv (in the archistriatum) and LPO (in the medial striatum). Neuronal ensembles in these regions could code the chick's anticipation for forthcoming events, particularly the quality/quantity and the temporal proximity of rewards. Without the internal representation of the anticipated proximity in LPO, behavioral tolerance will be lost, and the chick makes impulsive choice for a less optimized option. Functional roles of these regions proved compatible with their anatomical counterparts in the mammalian brain, thus suggesting that the neural systems linking between the memorized past and the anticipated future have remained highly conservative through the evolution of the amniotic vertebrates during the last 300 million years. With the conservative nature in mind, research efforts should be oriented toward a unifying theory, which could explain behavioral deviations from optimized foraging, such as "naïve curiosity," "contra-freeloading," "Concorde fallacy," and "altruism."

Time-dependent effects of cycloheximide on long-term memory in the cuttlefish

When shown prawns in a glass tube, cuttlefish promptly learn to inhibit their predatory behavior and retain this ability for a long time. The cellular and molecular mechanisms of this long-term memory (LTM) are not yet known. In this study, we analyzed the dependency of LTM on de novo brain protein synthesis. Cycloheximide (CXM), a protein synthesis inhibitor, is injected intravenously immediately, 1 h, 3 h, 4 h or 6 h after the training. Retention is tested 24 h posttraining. The injections of CXM revealed one period of memory sensitivity to pharmacological intervention. CXM administered immediately or 6 h after training has no effect on LTM. Conversely, injections given between 1 and 4 h posttraining resulted in amnesia. Taken together, findings of this study establish for the first time in Sepia officinalis that de novo protein synthesis is an essential and time-dependent event for LTM formation of this form of associative learning.

Time course of protein synthesis-dependent phase of olfactory memory in the cricket Gryllus bimaculatus

The cricket Gryllus bimaculatus forms a stable olfactory memory that lasts for practically a lifetime. As a first step to elucidate the cellular mechanisms of olfactory learning and memory retention in crickets, we studied the dependency of memory retention on the de novo brain protein synthesis by injecting the protein synthesis inhibitor cycloheximide (CHX) into the head capsule. Injection of CHX inhibited (3)H-leucine incorporation into brain proteins by > 90% for 3 hr. Crickets were trained to associate peppermint odor with water (reward) and vanilla odor with saline solution (non-reward) and were injected with CHX before or at different times after training. Their odor preferences were tested at 2 hr, 1 day and 4 days after training. Memory retention at 2 hr after training was unaffected by CHX injection. However, the level of retention at 1 day and 4 days after training was lowered when CHX was injected 1 hour before training or at 1 hr or 6 hr after training. To study the time course of the development of CHX-sensitive memory phase, crickets that had been injected with CHX at 1 hr after training were tested at different times from 2 to 12 hr after training. The level of retention was unaffected up to 4 hr after training but significantly lowered at 5 hr after training, and the CHX-sensitive memory phase developed gradually during the next several hours. CHX dissociates two phases of olfactory memory in crickets: earlier protein synthesis-independent phase (< 4 hr) and later (> 5 hr) protein synthesis-dependent phase.

Analysis of differential gene expression supports a role for amyloid precursor protein and a protein kinase C substrate (MARCKS) in long-term memory

Previous work has identified the intermediate and medial part of the hyperstriatum ventrale (IMHV) as a region of the chick brain storing information acquired through the learning process of imprinting. We have examined in this brain region changes in expression of candidate genes involved in memory. Chicks were exposed to a rotating red box and the strength of their preference for it, a measure of learning, determined. Brain samples were removed approximately 24 h after training. Candidate genes whose expressions were different in IMHV samples derived from strongly imprinted chicks relative to those from chicks showing little or no learning were identified using subtractive hybridization. The translation products of two candidate genes were investigated further in samples from the left and right IMHV and from two other brain regions not previously implicated in imprinting, the left and right posterior neostriatum. One of the proteins was the amyloid precursor protein (APP), the other was myristoylated alanine rich C kinase substrate (MARCKS). In the left IMHV the levels of the two proteins increased with the strength of learning. The effects in the right IMHV were not significantly different from those in the left. There were no effects of learning in the posterior neostriatum. This is the first study to relate changes in the amounts of MARCKS and APP proteins to the strength of learning in a brain region known to be a memory store and demonstrates that the systematic identification of protein molecules involved in memory formation is possible.

Neural cell adhesion molecule-mediated neurite outgrowth is repressed by overexpression of HES-1

The neural cell adhesion molecule (NCAM) stimulates neurite outgrowth by activating intracellular signaling cascades. We investigated the role of the transcriptional repressor HES-1 in NCAM-dependent neurite outgrowth by estimating neurite extension from PC12-E2 cells grown in coculture with NCAM-negative or NCAM-positive fibroblasts. PC12-E2 cells were transiently transfected with an expression plasmid encoding HES-1. We found that expression of HES-1 inhibited NCAM-dependent neurite outgrowth. Treatment with arachidonic acid (an important messenger in NCAM-dependent signaling) restored NCAM-induced neurite outgrowth inhibited by HES-1. These results suggest that HES-1 is a regulator of intracellular signal transduction stimulated by cell adhesion molecules involved in neurite outgrowth.

Lesions of the ventro-medial basal ganglia impair the reinforcement but not the recall of memorized color discrimination in domestic chicks

Effects of bilateral chemical lesions of the ventro-medial basal ganglia (lobus parolfactorius, LPO) were examined in 3-9-day-old domestic chicks. In experiment-1, chicks were trained to peck at a blue bead that was associated with drops of water as a reward. Addition of passive avoidance training using a bitter yellow bead resulted in highly selective pecking between blue and yellow. LPO lesion (given 3-5 h after training) did not impair the selectivity when chicks were tested 24 h afterwards, while the novel reinforcement using a red bead was severely impaired. In experiment-2, chicks were trained in a GO/NO-GO color discrimination task with food reward. Trained chicks received bilateral LPO lesions, and they were tested 48 h afterwards for the number of pecks and latency of the first peck in each trial. The LPO lesion did not impair the recall of memorized color discrimination in tests, while the chicks were severely deficient in post-operative novel training. These results confirm that: (1) bilateral LPO ablation does not interfere with selective pecking based on the memorized color cues; but (2) it impairs reinforcement in novel training. LPO is thus supposed to be involved in acquisition, rather than execution of memorized behaviors.

Effects of predictable and unpredictable intermittent noise on spatial learning in rats

The effects of predictable (periodic) and unpredictable (aperiodic) intermittent noise of moderate intensity (68 dB) on the learning of a complex T-maze by genetically defined rats were investigated. In Experiment 1, three groups (n=8) of rats learned a multiple T-maze, one group under control conditions, one group with predictable intermittent noise and one group with unpredictable intermittent noise. Results showed a profound effect of noise on learning and behavioural scores. Noise-exposed animals made less errors, finished their trials sooner and explored less. There was no difference between predictable and unpredictable noise. Further tests, during which formerly noise-exposed groups learned a new route under control conditions (Experiment 2) or the former controls learned a new route with noise (Experiment 3), suggest that the effects of noise on learning were caused by an effect of noise on memory formation and/or retrieval, rather than by long-term shifts in behavioural strategies.

Nicotine self-administration impairs hippocampal plasticity

Nicotine, the neuroactive compound responsible for tobacco addiction, is primarily believed to have beneficial effects on the adult brain. However, in heavy smokers, abstinence from nicotine is accompanied by cognitive impairments that suggest adverse effects of nicotine on brain plasticity. For this reason, we studied changes in plasticity-related processes in the dentate gyrus (DG) of the hippocampal formation of animals trained to self-administer nicotine. The DG was chosen because it undergoes profound plastic rearrangements, many of which have been related to memory and learning performances. In this region, we examined the expression of the polysialylated (PSA) forms of neural cell adhesion molecule (NCAM), PSA-NCAM, neurogenesis, and cell death by measuring the number of pyknotic cells. It was found that nicotine self-administration profoundly decreased, in a dose-dependent manner, the expression of PSA-NCAM in the DG; a significant effect was observed at all the doses tested (0.02, 0.04, and 0.08 mg/kg per infusion). Neurogenesis was also decreased in the DG, but a significant effect was observed only for the two highest doses of nicotine. Finally, the same doses that decreased neurogenesis also increased cell death. These results raise an important additional concern for the health consequences of nicotine abuse and open new insight on the possible neural mechanisms of tobacco addiction.

Forced swimming evokes a biphasic response in CREB phosphorylation in extrahypothalamic limbic and neocortical brain structures in the rat

The transcription factor cAMP response element-binding protein (CREB) plays a critical role in plasticity processes underlying learning and memory. We investigated the phosphorylation of CREB in rat brain after forced swimming, a stressor known to impact on higher limbic and neocortical brain areas. As shown by immunohistochemistry, forced swimming increased phosphorylated CREB (P-CREB) levels in the dentate gyrus, all neocortical areas, the medial, lateral and basolateral nuclei of the amygdala, cerebellum but not in the hypothalamic paraventricular nucleus. Distinct differences in the P-CREB pattern were observed in the deeper vs. superficial layers of the neocortex. The response in P-CREB was stressor type-specific because exposure to either ether or a cold environment was ineffective. The forced swimming-induced changes in P-CREB levels showed a biphasic time-course: an early peak detected at 15 min was followed by a marked drop at 60 min; a second rise starting after 1-2 h, reached maximal values between 6 and 8 h, and remained elevated for at least 48 h. Examination of the neuroanatomical induction pattern of the CRE-inducible immediate early gene product c-fos revealed that it was only partly overlapping with that of P-CREB. Western analyses showed that only the 43-kDa CREB protein (an enhancer of CRE-containing promotors) was phosphorylated after forced swimming, while other members of the CREB/ATF family (CREM, ATF-1 and ATF-2) remained unaffected. The NF-kappaB pathway was not activated, indicating that forced swimming does not unspecifically evoke transcription factor activation. Thus, in contrast to physical stressors, such as ether or cold exposure, forced swimming, a stressor with a strong psychological component, elicits the recruitment of the CREB pathway in a widespread manner in the limbic system and neocortex; brain regions known to be implicated in various forms of (stress-related) learning and memory.

The transcription factors CREB and c-Fos play key roles in NCAM-mediated neuritogenesis in PC12-E2 cells

The neural cell adhesion molecule (NCAM) stimulates axonal outgrowth by activation of the Ras-mitogen activated protein kinase (MAPK) pathway and by generation of arachidonic acid. We investigated whether the transcription factors, cyclic-AMP response-element binding protein (CREB) and c-Fos play roles in this process by estimating NCAM-dependent neurite outgrowth from PC12-E2 cells grown in co-culture with NCAM-negative or NCAM-positive fibroblasts. PC12-E2 cells were transiently transfected with expression plasmids encoding wild-type or dominant negative forms of CREB and c-Fos or an activated form of the MAPK kinase, MEK2. Alternatively, PC12-E2 cells were treated with arachidonic acid, the cAMP analogue dBcAMP, or protein kinase A (PKA) inhibitors. The negative forms of CREB and c-Fos inhibited neurite outgrowth mediated by NCAM, arachidonic acid, dBcAMP, or MEK2. Neither CREB nor c-Fos could compensate for the inactivation of the other, indicating that both factors are important in NCAM-mediated neuritogenesis. Treatment of primary hippocampal neurons with a synthetic NCAM peptide ligand known to stimulate neurite outgrowth induced phosphorylation of CREB and expression of c-fos. We thus present evidence that NCAM-mediated neurite outgrowth involves a series of signal transduction pathways, including the cAMP/PKA pathway, targeting c-Fos and CREB.

Reversed effects of RU486 and anisomycin on memory retention of light exposure or corticosterone facilitation in the dark-incubated chicks

Memory formation for a weak passive avoidance task in the dark-incubated chicks is facilitated by light exposure or corticosterone administration at optimally pre-hatch time points. To explore the potential mechanisms underlying activation of brain memory function development by light or corticosterone exposure during late embryo, steroid receptor antagonist RU486, or protein synthetic inhibitor anisomycin, was administered intraembryonically to the embryos of either only 24-h light-exposure or complete dark-hatched on embryonic day 20 (E20). The results showed that RU486 and anisomycin significantly retarded the facilitated retention both by light and corticosterone exposure in the dark-incubated chicks. They also suggest that the act of corticosterone or light exposure on the development of brain memory function is mediated by the effect of steroid receptor, or afterward on related protein syntheses that is involved in memory formation of post-hatched performance of day-old chicks.

Stress alleviates reduced expression of cell adhesion molecules (NCAM, L1), and deficits in learning and corticosterone regulation of apolipoprotein E knockout mice

Cell adhesion molecules (CAMs) involved in synaptic changes underlying learning and memory processes, are implicated in the effect of stress on behavioural performance. The present study was designed to test the hypothesis that (i) expression of CAMs is apolipoprotein E- (apoE) genotype dependent and (ii) repeated exposure to stress modulates the synthesis of CAMs in an apoE-genotype dependent manner. Using ELISA we tested this hypothesis and measured expression of NCAM and L1 in different brain regions of naïve and stressed apolipoprotein E-knockout (apoE0/0) and C57Bl6 (wild-type) mice. Naïve apoE0/0 mice had elevated basal morning corticosterone and ACTH concentrations and decreased expression of NCAM and L1 compared to wild-type mice. Repeated exposure of mice to rats, as the common stressor, alleviated the reduction in expression of CAMs in apoE0/0 mice; seven days after the last rat exposure, expression of NCAM was increased in frontal brain and hippocampus whereas expression of L1 was increased in hippocampus and cerebellum. Rat stress attenuated the elevation of basal morning corticosterone concentration in apoE0/0 mice towards concentrations detected in wild-type mice. Moreover, rat stress improved learning and memory of apoE0/0 mice in the water maze. In conclusion, repeated exposure to stress eliminated apoE-genotype-related differences in expression of CAMs. Under these same conditions the differences in cognitive performance and corticosterone concentrations were abolished between wild type and apoE0/0 mice.

Association of the HNK-1 epitope with the detergent-soluble G4 isoform of acetylcholinesterase from human neuroblastoma cells

The HNK-1 carbohydrate epitope is expressed in neural and natural killer cells and is a mediator of cell adhesion. It is well documented that acetylcholinesterase has a secondary function in cell adhesion and differentiation. The presence of HNK-1 on isoforms of Torpedo and Electrophorus acetylcholinesterase, as well as isoforms from the bovine central nervous system has been described. In this paper, we have investigated the association of the epitope with acetylcholinesterase from human neuroblastoma cells. Acetylcholinesterase was extracted, with or without detergent, purified on immunoaffinity columns and the isoforms separated by sucrose density gradient sedimentation. Secreted acetylcholinesterase, from spent serum-free culture medium, was similarly treated. The presence of the HNK-1 epitope was determined by ELISA using the anti-HNK-1 and Elec 39 monoclonal antibodies. The epitope was found to be associated with the detergent-soluble G4 isoform, but not with the hydrophilic G1 nor the secreted hydrophilic G4 isoforms. Likewise, no HNK-1 was observed associated with human erythrocyte acetylcholinesterase. These results indicate that acetylcholinesterase-G4, anchored in the extracellular membrane, is capable of mediating cell-substrate adhesion through HNK-1.

Drosophila fasciclinII is required for the formation of odor memories and for normal sensitivity to alcohol

Drosophila fasciclinII (fasII) mutants perform poorly after olfactory conditioning due to a defect in encoding, stabilizing, or retrieving short-term memories. Performance was rescued by inducing the expression of a normal transgene just before training and immediate testing. Induction after training but before testing failed to rescue performance, showing that Fas II does not have an exclusive role in memory retrieval processes. The stability of odor memories in fasII mutants are indistinguishable from control animals when initial performance is normalized. Like several other mutants deficient in odor learning, fasII mutants exhibit a heightened sensitivity to ethanol vapors. A combination of behavioral and genetic strategies have therefore revealed a role for Fas II in the molecular operations of encoding short-term odor memories and conferring alcohol sensitivity. The preferential expression of Fas II in the axons of mushroom body neurons furthermore suggests that short-term odor memories are formed in these neurites.

Reward-related neuronal activities in basal ganglia of domestic chicks

We aimed to reveal what is coded in the basal ganglia of domestic chicks. In the water-reinforced 'go' task, chicks learned to peck selectively at a colored bead in order to obtain a drop of water. Out of 38 units obtained, seven showed excitatory activities specifically during the reward period. In the food-reinforced go/no-go task, chicks learned to discriminate two colors to obtain mash food after a delay period. They also learned to ignore another color, which was not associated with a reward. Out of 27 units obtained, four showed excitatory activities during the cue period, specifically when a food reward was anticipated. LPO neurons may code qualities of the obtained rewards, and also chick's anticipation of the forthcoming rewards.

Extracellular calcium depletion as a mechanism of short-term synaptic depression

Recent experiments have demonstrated that normal neural activity can cause significant decrements in external calcium levels, and that these decrements mediate a form of short-term synaptic depression. These findings raise the possibility that certain forms of short-term synaptic depression at glutamatergic synapses throughout the mammalian CNS may be influenced by similar changes in external calcium. We use a computational model of the extracellular space, combined with experimental data on calcium consumption, to show that such short-term depression can be accounted for by changes in calcium just outside active synapses, provided that external calcium diffusion is restricted. Remarkably, the model suggests the novel possibility that synapses may possess private pools of external calcium that enforce some forms of short-term depression in a synapse-specific manner.

An approach to the complexity of the brain

The establishment of ordered neuronal connections is supposed to take place under the control of specific cell adhesion molecules (CAM) which guide neuroblasts and axons to their appropriate destination. The extreme complexity of the nervous system does not provide a favorable medium for the development of deterministic connections. Simon's [112] theorems offer a mean to approach the high level of complexity of the nervous system. The basic tenet is that complex systems are hierarchically organized and decomposable. Such systems can arise by selective trial and error mechanisms. Subsystems in complex systems only interact in an aggregate manner, and no significant information is lost if the detail of aggregate interactions is ignored. A number of nervous activities, which qualify for these requirements, are shown. The following sources of selection are considered: internal and external feedbacks, previous experience, plasticity in simple structures, and the characteristic geometry of dendrites. The role played by CAMs and other membrane-associated molecules is discussed in the sense that they are either inductor molecules that turn on different homeobox genes, or downstream products of genes, or both. These molecules control cellular and tissular differentiation in the developing brain creating sources of selection required for the trial and error process in the organization of the nervous tissue.

Assessment of neural cell adhesion molecule (NCAM) in autistic serum and postmortem brain

Studies have identified structural abnormalities in areas of the autistic brain, with a pattern suggesting that a neurodevelopmental anomaly took place. Neural cell adhesion molecule (NCAM), which is involved in development of the central nervous system, was previously shown to be decreased in the serum of autistic individuals. In the present study, we measured NCAM protein in the sera from controls, patients with autism, siblings of autistic patients, and individuals with other neurologic disorders, but found no significant differences. We also measured NCAM protein in autistic postmortem brain samples and found the longest isoform, NCAM-180, to be significantly decreased. In addition, we investigated the mRNA expression of NCAM in these brain samples using cDNA microarrays and RT-PCR. Results show that NCAM mRNA levels are not altered in autism.

Glycosylation of proteins during a critical time window is necessary for the maintenance of long-term potentiation in the hippocampal CA1 region

This paper focuses on the role of glycoproteins in activity-dependent synaptic plasticity. The effect of the different inhibitors of protein glycosylation, Tunicamycin, Brefeldin A and Swainsonine, on long-term potentiation was studied in the CA1 region of rat hippocampal slices. Bath application of the inhibitors 60 min before and during tetanization did not interfere with the induction of long-term potentiation of the field excitatory postsynaptic potential. However, the potentiation in inhibitor-treated slices decreased to baseline levels during 90-180 min. Significant differences in the potentiation in non-treated slices were detectable 80 min (Tunicamycin), 60 min (Brefeldin A) and 75 min (Swainsonine) after tetanization, thus indicating the prevention of long-term potentiation maintenance. The application of Swainsonine 120 and 240 min after tetanization did not influence the potentiated field excitatory postsynaptic potential. These data demonstrate the need for undisturbed glycoprotein processing in a time window around long-term potentiation induction to maintain later phases of long-term potentiation and essential functional implications of protein glycosylation in mechanisms underlying synaptic plasticity.