Increased incorporation of [3H]fucose into chick brain glycoproteins following training on a passive avoidance task

Feed your microbiome and improve sleep, stress resilience, and cognition

The brain and gut are connected both physically and biochemically. The gut-brain axis includes the central nervous system, neuroendocrine and neuroimmune systems, the enteric nervous system and vagus nerve, and the gut microbiome. It can influence brain function and even behavior, suggesting that dietary interventions may help enhance and protect mental health and cognitive performance. This review focuses on the role of the microbiome and its metabolites in sleep regulation, neurodegenerative disorders, mechanisms of stress, and mood. It also provides examples of nutritional interventions which can restore healthy gut microbiota and aid with risk reduction and management of many disorders related to mental and cognitive health. Evidence suggests a shift in the gut microbiota towards a balanced composition could be a target to maintain brain health, reduce stress and improve quality of life.

Human and Bovine Milk Oligosaccharides Elicit Improved Recognition Memory Concurrent With Alterations in Regional Brain Volumes and Hippocampal mRNA Expression

Human milk contains a unique profile of oligosaccharides (OS) and preliminary evidence suggests they impact brain development. The objective of this study was to assess the impact of bovine and/or human milk oligosaccharides (HMO) (2′-fucosyllactose and Lacto-N-neotetraose) on cognition, brain development, and hippocampal gene expression. Beginning on postnatal day (PND) 2, male pigs received one of four milk replacers containing bovine milk oligosaccharides (BMOS), HMO, both (BMOS + HMO), or neither. Pigs were tested on the novel object recognition task using delays of 1- or 48-h at PND 22. At PND 32–33, magnetic resonance imaging procedures were used to assess structural brain development and hippocampal tissue was collected for analysis of mRNA expression. Pigs consuming only HMO exhibited recognition memory after a 1-h delay and those consuming BMOS + HMO exhibited recognition memory after a 48-h delay. Both absolute and relative volumes of cortical and subcortical brain regions were altered by diet. Hippocampal mRNA expression of GABRB2, SLC1A7, CHRM3, and GLRA4 were most strongly affected by diet. HMO and BMOS had distinct effects on brain structure and cognitive performance. These data suggest different mechanisms underlie their influence on brain development.

Dietary Oligofructose Alone or in Combination with 2'-Fucosyllactose Differentially Improves Recognition Memory and Hippocampal mRNA Expression

Mounting evidence suggests that dietary oligosaccharides promote brain development. This study assessed the capacity of oligofructose (OF) alone or in combination with 2'-fucosyllactose (2'-FL) to alter recognition memory, structural brain development, and hippocampal gene expression. Beginning on postnatal day (PND) 2, male pigs received one of three milk replacers formulated to contain OF, OF + 2'-FL, or no oligosaccharides (CON). Pigs were tested on the novel object recognition task using delays of 1 or 48 h at PND 22. At PND 32-33, magnetic resonance imaging (MRI) procedures were used to assess structural brain development and hippocampal tissue was collected for analysis of mRNA expression. Pigs that consumed the OF diet demonstrated increased recognition memory after a 1 h delay, whereas those consuming diets containing OF + 2'-FL displayed increased recognition memory after a 48 h delay. Pigs fed OF or OF + 2'-FL exhibited a larger relative volume of the olfactory bulbs compared with CON pigs. Provision of OF or OF + 2'-FL altered gene expression related to dopaminergic, GABAergic, cholinergic, cell adhesion, and chromatin remodeling processes. Collectively, these data indicate that dietary OF and OF + 2'-FL differentially improve cognitive performance and affect olfactory bulb structural development and hippocampal gene expression.

Dietary 2'-Fucosyllactose Enhances Operant Conditioning and Long-Term Potentiation via Gut-Brain Communication through the Vagus Nerve in Rodents

2´-fucosyllactose (2´-FL) is an abundant human milk oligosaccharide (HMO) in human milk with diverse biological effects. We recently reported ingested 2´-FL stimulates central nervous system (CNS) function, such as hippocampal long term potentiation (LTP) and learning and memory in rats. Conceivably the effect of 2´-FL on CNS function may be via the gut-brain axis (GBA), specifically the vagus nerve, and L-fucose (Fuc) may play a role. This study had two aims: (1) determine if the effect of ingested 2´-FL on the modulation of CNS function is dependent on the integrity of the molecule; and (2) confirm if oral 2´-FL modified hippocampal LTP and associative learning related skills in rats submitted to bilateral subdiaphragmatic vagotomy. Results showed that 2´-FL but not Fuc enhanced LTP, and vagotomy inhibited the effects of oral 2´-FL on LTP and associative learning related paradigms. Taken together, the data show that dietary 2´-FL but not its Fuc moiety affects cognitive domains and improves learning and memory in rats. This effect is dependent on vagus nerve integrity, suggesting GBA plays a role in 2´-FL-mediated cognitive benefits.

Effects of a human milk oligosaccharide, 2'-fucosyllactose, on hippocampal long-term potentiation and learning capabilities in rodents

Human milk oligosaccharides (HMOs) are unique with regard to their diversity, quantity and complexity, particularly in comparison to bovine milk oligosaccharides. HMOs are associated with functional development during early life, mainly related to immunity and intestinal health. Whether HMOs elicit a positive effect on cognitive capabilities of lactating infants remains an open question. This study evaluated the role of the most abundant HMO, 2'-fucosyllactose (2'-FL), in synaptic plasticity and learning capabilities in rodents. Mice and rats were prepared for the chronic recording of field excitatory postsynaptic potentials evoked at the hippocampal CA3-CA1 synapse. Following chronic oral administration of 2'-FL, both species showed improvements in input/output curves and in long-term potentiation (LTP) evoked experimentally in alert behaving animals. This effect on LTP was related to better performance of animals in various types of learning behavioral tests. Mice were tested for spatial learning, working memory and operant conditioning using the IntelliCage system, while rats were submitted to a fixed-ratio schedule in the Skinner box. In both cases, 2'-FL-treated animals performed significantly better than controls. In addition, chronic administration of 2'-FL increased the expression of different molecules involved in the storage of newly acquired memories, such as the postsynaptic density protein 95, phosphorylated calcium/calmodulin-dependent kinase II and brain-derived neurotrophic factor in cortical and subcortical structures. Taken together, the data show that dietary 2'-FL affects cognitive domains and improves learning and memory in rodents.

Cerebral Glycoprotein Synthesis and Long-term Memory Formation in the Chick (Gallus domesticus) Following Passive Avoidance Training Depends on the Nature of the Aversive Stimulus

Chicks that peck a small bright bead coated in a distateful substance can learn in a single trial to subsequently avoid a similar bead. The taste aversant commonly used is methyl anthranilate, which also has a strong pervasive odour. We have compared the efficacy of methyl anthranilate and the apparently odourless quinine as aversants. Methyl anthranilate-trained chicks learnt the task and the memory apparently persisted undiminished for at least 24 h. Quinine-trained chicks exhibited a memory for the task similar to that of methyl anthranilate-trained chicks 45 min after training, this thereafter declined until, at 24 h after training, they showed no recall. We investigated the incorporation of a radio-labelled synaptic membrane glycoprotein precursor, [3H]fucose, into three regions of the chick forebrain; two of these regions have previously been implicated in learning using methyl anthranilate as the aversant. There was a significant increase in [3H]fucose incorporation into the left lateral cerebral area and numerically similar, but non-significant, increases in the intermediate part of the medial hyperstriatum ventrale and lobus parolfactorius. There were no such increases in the right hemisphere of methyl anthranilate-trained chicks or any region of either hemisphere of quinine-trained chicks. Thus, the memory for methyl anthranilate is longer-lasting than that for quinine and is associated with increased fucosylation in the left cerebral hemisphere and although in the short-term, chicks can retain a memory of the one-trial passive avoidance task with quinine as the aversant, this does not result in a localized increase in cerebral [3H]fucose incorporation.

Immunoglobulin superfamily members gp65 and gp55: tissue distribution of glycoforms

Gp65 and gp55 are immunoglobulin superfamily members produced by alternative splicing of the same gene transcript, and originally identified as components of synaptic membranes. A monoclonal antibody specific for gp65 and gp55 has been used to detect immunoreactive species in a wide range of tissues. All immunoreactive species bind to concanavalin A and deglycosylation studies show that in all tissues tested other than brain the immunoreactive species are derived from gp55. HEK cells transfected with gp65 or gp55 express different glycoforms from brain showing that the pattern of glycosylation of these molecules is dependent upon the cell type in which they are expressed.

Cell adhesion molecules and the transition from short- to long-term memory

Training chicks on a one-trial passive task results in a cascade of molecular and cellular processes in two forebrain regions, culminating within 60-90 min in post-translational glycosylation of synaptic membrane proteins and expression of immediate early genes c-fos and c-jun. We have found a second window of vulnerability of memory to the protein synthesis inhibitor anisomycin, 4 h downstream of training. By 5.5 h post-training this window closes, to be replaced by a window of sensitivity to blockade of glycoprotein synthesis, presumably representing post-translational modification of the newly synthesised proteins. Amongst the pre- and post-synaptic membrane glycoproteins involved it both first and second time windows are the cell adhesion molecules, L1 (at both times) and NCAM (at the later). Molecular dissection of the external membrane domains of L1 distinguishes between a requirement for the IgG domain at the early time, the fibronectin-like domain at the later. The second time window only occurs if the animal is trained on a stimulus strong enough to be remembered for a long period. Weak memories do not persist beyond 6-8 h and the second wave of glycoprotein synthesis does not occur. Thus the second wave may represent the molecular processes required for the alterations in synaptic configuration, by way of the adhesion molecules amongst others, required for the morphological changes in neuronal connectivity hypothesised to encode memory.

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

The transition from short- to long-term memory requires lasting modulations of synaptic connectivity. In a variety of species and learning tasks, enhanced synthesis of glycoprotein cell-adhesion molecules (CAMs), such as neural CAM (NCAM) and Ll, 5-8 h post-training is a necessary step in this process. If the training event is weak, this phase of glycoprotein synthesis does not occur and memory is not retained. Antibodies or fragments that bind to the extracellular domains of NCAM or Ll at this time produce amnesia for the task. Centrally administered corticosterone enhances retention of weak learning, and steroid-receptor antagonists are amnestic. The effects of corticosterone are mediated through synthesis of 'second-wave' glycoproteins. As 'nootropic' drugs such as piracetam only enhance long-term retention and are ineffective in adrenalectomized animals, the interaction between glucocorticoids and glycoproteins might provide a site for pharmacological intervention in alleviating the losses of memory that occur in neurodegenerative disorders.

The biochemistry of learning and memory

An overview of some of the biochemical and molecular events involved in the process of learning and memory are presented in a short review. Two invertebrate models of learning are considered: the gill-withdrawal reflex of Aplysia and avoidance learning in Drosophila melanogaster. Particular attention is paid to the biochemical mechanisms underlying both the development of long-term potentiation (LTP) and passive avoidance learning (PAL) in the young chick. The role of several biological molecules in learning and memory are considered, for example, protein kinase C (PKC), Ca(++)-Calmodulin kinase II (CaMKII), GAP-43, and glutamate receptors.

A role for a chicken homolog of the neural cell adhesion molecule L1 in consolidation of memory for a passive avoidance task in the chick

Intracranial injection of antibodies directed against the neural cell adhesion molecule L1 resulted in amnesia for passive avoidance training in day-old chicks tested 24 hr subsequently. L1 antibodies were amnesic when administered at one of two time windows: 30 min pretraining and 5.5-8 hr post-training. No amnesia was apparent if injections were made at times before, between, or after these time windows (-2, +1, +3, +4, or +12 hr relative to training). A fragment of the L1 molecule derived from the external fibronectin domains FN1-5 produced amnesia only when injected at the 5.5-hr timepoint, whereas a fragment of the immunoglubin-like domains Ig I-VI produced amnesia only when injected 30 min prior to training. We have shown previously that long-term memory for the passive avoidance task requires two waves of glycoprotein synthesis, the first occurring immediately after training, and the second some 6 hr thereafter. The glycoprotein synthesis inhibitor 2-deoxygalactose results in amnesia if injected at either time, whereas the neural cell adhesion molecule (N-CAM) is specifically involved only in the second wave. The coincidence of the time course of memory disruption resulting from injection of L1 antibodies with that occurring with 2-deoxygalactose supports the hypothesis that establishment of an enduring memory for the experience of passive avoidance training requires two waves of glycoprotein synthesis, each wave being biochemically and functionally discrete. The differential effects of the two L1 fragments suggests that separate mechanisms of synaptic stabilization are involved at the two time points.

Dendritic spine density in the lobus parolfactorius of the domestic chick is increased 24 h after one-trial passive avoidance training

One to three day old chicks spontaneously peck at small objects. When presented with a chrome bead coated with the bitter tasting substance methyl anthranilate (MeA), chicks peck once, display a characteristic disgust response and subsequently avoid a similar bead. Chicks that are trained on a water coated bead continue to peck a similar bead on retrial. Twenty four hours after training on this one-trial passive avoidance paradigm, chicks were tested for retention. The brains of chicks displaying the correct behavioural response (> 90%) were removed and the lobus parolfactorius from each hemisphere was dissected from the brain and impregnated using a rapid Golgi technique. Analysis of large multipolar neurones by centrifugal dendritic branch order showed that there were significantly more spines on all orders examined in the left hemispheres of MeA-trained chicks compared to water-trained control chicks. Significantly higher spine densities were also found on 4th and 5th order branches of neurones in the right lobus parolfactorius of MeA-trained chicks compared to water-trained chicks. No significant difference in dendritic length was observed. These results suggest that substantial plasticity occurs in post-synaptic structures in the lobus parolfactorius following passive avoidance training. It is suggested that this plasticity is related to processes involved in long term information storage.

Corticosteroid receptor antagonists are amnestic for passive avoidance learning in day-old chicks

Glucocorticoids can modulate behavioural processes and neural plasticity. They are released during learning situations and can trigger neural actions through binding to brain receptors. We hypothesized that a glucocorticoid action could play a critical role in the mechanisms involved in long-term memory formation. In order to test this hypothesis, chicks were trained on a passive avoidance learning task and given bilateral intracerebral injections of selective mineralocorticoid (RU-28318) or glucocorticoid (RU-38486) receptor antagonists. The results showed that both antagonists alter information processing when injected prior to the training session. Possible state-dependent effects were discharged. Further experiments evaluating possible effects of the antagonists on concomitant aspects of the learning situation (such as novelty reaction and pecking pattern) indicated that, as opposed to the glucocorticoid receptor antagonist, the mineralocorticoid antagonist altered the birds' reactivity to non-specific aspects of the training task. These results suggest that the two types of intracellular corticosteroid receptors could be mediating different aspects of the information processing and storage involved in avoidance learning. In addition, this study points out that passive avoidance learning in the chick could be a good model to investigate the biochemical mechanisms involved in corticosteroid actions on learning-induced neural plasticity.

2-deoxygalactose interferes with an intermediate processing stage of memory

The effect of 2-deoxygalactose (2-D-gal), an inhibitor of glycoprotein synthesis, on memory formation was investigated with the day-old chick trained on a single-trial passive discrimination task. 2-D-gal (10 mumol/chick) was shown to inhibit memory formation at a time before the emergence of an antibiotic-sensitive long-term memory stage. The amnestic effect of 2-D-gal was successfully prevented by galactose, and more significantly by noradrenaline. In contrast, anisomycin-induced amnesia was resistant to challenge by either galactose or noradrenaline. The results are consistent with the view that some glycoprotein involvement in memory formation occurs prior to the formation of protein synthesis-dependent long-term memory, and this role of glycoproteins may be associated with the triggering of long-term memory formation by noradrenaline.

A role for the neural cell adhesion molecule in a late, consolidating phase of glycoprotein synthesis six hours following passive avoidance training of the young chick

We have investigated the effect of intracranial injections of the amnestic anti-metabolite, 2-deoxygalactose, and antibodies to the neural cell adhesion molecule on retention of a one-trial passive avoidance task in chicks. Groups of chicks received bilateral intracranial injections of 10 mumol/hemisphere 2-deoxygalactose or 10 microliters/hemisphere anti-neural cell adhesion molecule and were tested 24 h following training. 2-Deoxygalactose injections were amnestic when administered at a previously established time (30 min pre-training). Here we show that the agent is also amnestic when injected within a second time window occurring specifically 6-8 h after training. Administration of 2-deoxygalactose between 2 and 6 h or after 8 h post-training was without effect on retention tested 24 h following training. Anti-neural cell adhesion molecule injections were amnestic only when performed at a time which coincided with the second phase of 2-deoxygalactose susceptibility. Further experiments demonstrated that the neural cell adhesion molecule is one of the molecules into which 2-deoxygalactose is incorporated. Additionally, we investigated the extent of diffusion of 2-deoxygalactose and anti-neural cell adhesion molecule following their injection, with respect to their residence in forebrain loci known to be involved in the memory for passive avoidance. We interpret these data as indicating that two waves of glycoprotein synthesis are necessary for the establishment of long-term memory for the experience of passive avoidance training. The evidence is discussed in the context of earlier results indicating that the two waves involve different glycoprotein species and, possibly, different forebrain regions. We speculate that the late phase of glycoprotein synthesis coincides with, and is required for, modulation of cell-cell adhesion processes, reflecting the selection and stabilization of synapses which maintain an enduring representation of long-term memory.

Purified antichick Thy-1 IgG abolishes intermediate and long-term memory

One- to 2-day-old chicks administered purified antichick Thy-1 IgG showed substantial amnesia for a single-trial passive discriminated avoidance task. Amnesia was clearly evident at 30 min after learning, during the intermediate stage of a three-stage model of memory processing, and persisted for at least 3 h. A similar effect was also observed with Fab and F(ab')2 fragments. Fc fragments, the non-IgG fraction of ascites, and saline yielded normal retention levels at all times. These results contrast with our earlier reports that both polyclonal and monoclonal antibodies to chick Thy-1 inhibited long-term memory formation only. The present findings are interpreted as possibly representing a dual effect of the purified IgG.

The maintenance of hippocampal long-term potentiation is paralleled by a dopamine-dependent increase in glycoprotein fucosylation

Induction of long-term potentiation (LTP) in hippocampal slices of rats caused an increase in both protein synthesis and glycoprotein fucosylation by 38 and 34%, respectively. The enhanced incorporation of [3H]fucose into glycoproteins observed 1 h after tetanization was abolished in the presence of the dopamine D1 receptor antagonist SCH23390 during stimulation whereas the LTP-induced increase of protein synthesis was not influenced by this drug. The enhanced insertion of [3H]fucose into hippocampal glycoproteins 1 h after tetanization was paralleled by an increase in the activity of the fucose metabolizing enzyme, fucokinase. In contrast no changes in protein and glycoprotein synthesis were detectable 5 h after tetanization of the slices. The results provide evidence that in addition to an enhanced protein synthesis a dopamine (D1) mediated increase in glycoprotein fucosylation is necessary for the maintenance of the late stage of LTP.

Characterisation and regional localisation of pre- and postsynaptic glycoproteins of the chick forebrain showing changed fucose incorporation following passive avoidance training

To identify those glycoproteins whose synthesis or modification is necessary for memory formation, we have studied the uptake of radiolabelled fucose into synaptic plasma membranes (SPMs) and postsynaptic densities (PSDs) derived from two specific left and right forebrain loci, at two different times after training of 1-day-old chicks on a one-trial passive avoidance learning task. To increase the reliability of the comparison, a double-labelling method was used. Tissue samples from intermediate medial hyperstriatum ventrale (IMHV) and lobus parolfactorius (LPO) were isolated at 6 and 24 h after training. At both times, training resulted in region-specific changes, both increases and decreases, in incorporated radioactivity into pre- and postsynaptic glycoproteins. After 6 h, there was a relative decline in incorporation into both SPMs and PSDs of the right IMHV of trained chicks, a decline that persisted in the PSDs until 24 h. A small decline in incorporation in SPMs from the right LPO of trained chicks at 6 h was reversed by 24 h, by which time there was a 64% increase in incorporation into SPMs and a 24% increase into PSDs of the left LPO. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis of left and right hemisphere samples containing LPO revealed that 6 h after training the main effect was presynaptic, including a reduction of incorporation into high molecular mass glycoproteins, of 150-180 kDa, and an increase in a lower molecular mass (41 kDa) fraction. By 24 h after training, a left hemisphere presynaptic glycoprotein of molecular mass approximately 50 kDa showed the biggest increase in fucosylation. In addition, a wide group of postsynaptic glycoproteins of both hemispheres, in the ranges 150-180, 100-120, and 33 kDa now showed increases in incorporation. Some other fractions showed decreases. These results are in accord with previous data on incorporation obtained using the amnesic agent 2-deoxygalactose. They also support the hypothesis that memory formation involves the strengthening of connections between pre- and postsynaptic neurons of the LPO by growth or modulation of pre- and postsynaptic structures.

The effect of dark-rearing on dendritic development in two regions of the forebrain of the domestic chick

The effects of dark-rearing on dendritic development were studied in domestic chicks aged 72 h. Two areas of the forebrain were investigated, the hyperstriatum accessorium (HA) and the intermediate part of the medial hyperstriatum ventrale (IMHV). Dark-rearing significantly reduced spine density on the dendrites of large multipolar neurones in both left and right HA. In the IMHV there was a significant decrease in spine density in the left hemisphere in chicks reared in the light. No other parameters of dendritic development were affected. These results reinforce the conclusion that in the young domestic chick the left IMHV is a particularly labile region.

Effects of the amnesic agent 2-deoxygalactose on incorporation of fucose into chick brain glycoproteins

The interaction of the amnesic agent 2-deoxygalactose with fucose incorporation into glycoproteins in day-old chick forebrain has been studied with the aim of identifying glycoproteins whose synthesis is modified during memory formation. 2-Deoxygalactose inhibited total exogenous [14C]fucose incorporation into the forebrain glycoproteins by 26%. Sodium dodecyl sulphate-polyacrylamide gradient gel analysis revealed that intracerebrally injected 2-[3H]deoxygalactose labelled the same eight major glycoprotein bands as were identified using [14C]fucose labelling. Subsequent investigations focussed on these selected components. Subcellular fractionation showed that between 4 and 24 h after administration of the deoxy-sugar, the incorporated radioactivity was found predominantly at the synaptic sites, some glycoproteins being more abundant in synaptic plasma membranes and others in postsynaptic densities. This distribution pattern varied according to the time after injection. The effect of passive avoidance training, using a methylanthranilate-coated bead, on [14C]fucose incorporation into forebrain was to decrease fucose uptake into components of molecular mass 150-180 kilodaltons but to increase significantly labelling of glycoproteins of molecular mass 33 and 28 kilodaltons. The possible implications of these training-induced changes are discussed.

Passive avoidance learning produces focal elevation of bursting activity in the chick brain: amnesia abolishes the increase

Presentation of a bright bead to day-old chicks (Gallus domesticus: Ross 1 Chunky Chicks) elicits spontaneous pecking. If the bead is coated with an aversive substance (e.g., methylanthranilate), they will avoid similar beads subsequently; if it is coated with water, they peck avidly on re-presentation. Formation of a memory for this one-trial passive avoidance task is unaffected by subconvulsive transcranial electroshock when applied 10 min after training in 60% of birds, whereas "immediate" post-training electroshock renders 63% of chicks amnesic. Memory formation and retention is associated with a large bilateral enhancement in trained over control chicks (320 and 350% in left and right hemispheres, respectively; p less than 0.001) of a particular spontaneous multi-unit activity firing pattern, that is, short-duration (15-40 ms) bursts of large-amplitude (greater than or equal to 200 microV, 450 microV max p-p), high-frequency (400-450 Hz) spiking in anesthetized chicks. This effect is observed in data lumped from 1-13 h after training and is restricted to the intermediate medial hyperstriatum ventrale. When chicks are rendered amnesic by electroshock immediately following training, there is a complete abolition of this increase in burst firing; in those chicks where this treatment fails to elicit amnesia, the increase in bursting is still observed. In birds in which the shock is delayed and memory formation occurs, the increase in bursting activity is maintained; however, if the delayed shock produces apparent amnesia, then the increase is once again abolished. The electroshock had no effect on bursting per se in untrained chicks. There was no significant difference in tonic spiking between the chicks. A marked increase in the occurrence of bursting epochs in the IMHV of anesthetized chicks following passive avoidance training is therefore closely associated with memory formation, but not with the nonspecific concomitants of the training procedure.

Phosphorylation of synaptic proteins in chick forebrain: changes with development and passive avoidance training

We have used synaptic plasma membranes (SPMs) and postsynaptic densities (PSDs) to study protein phosphorylation at the synapse in the developing chick forebrain and in 1-day-old chick forebrain following training on a passive avoidance task. Endogenous phosphorylation patterns in SPMs and PSDs prepared by extraction with n-octylglucoside isolated from chick forebrain were investigated by labelling with [32P]ATP. The phosphoprotein components of the SPM and PSD fractions were separated using sodium dodecyl sulphate gradient polyacrylamide gel electrophoresis. Autoradiography and densitometry of the Coomassie Blue protein staining pattern revealed phosphate incorporation into several SPM components including those of molecular mass 52, 37, and 29 kilodaltons (kDa). Bands of similar molecular mass were not phosphorylated in PSD fractions. This difference in phosphorylation between SPMs and PSDs was not due to the detergent n-octylglucoside. In a developmental study in which SPM and PSD fractions were prepared from 1-day-old, 14-day-old, and 21-day-old chickens, the phosphorylation patterns of SPMs were similar throughout, but striking differences occurred in PSDs, both in the level of phosphorylation and in the components phosphorylated. A time-course study was carried out in which phosphorylation of SPMs and PSDs from 1-day-old chicks trained on a passive avoidance task was compared with patterns from control chicks trained on a water-coated bead and untrained chicks. In SPMs prepared from forebrains removed 10 mins following training, a consistent but nonsignificant decrease (-21%) in phosphorylation of a 52 kDa band occurred in chicks with passive avoidance training compared with water-trained and untrained chicks.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term memory formation in chicks is blocked by 2-deoxygalactose, a fucose analog

When day-old chicks are trained on a passive avoidance task there is enhanced synthesis of glycoproteins. Bilateral intracerebral injections of 20 mumole of 2-deoxygalactose (2-D-gal), administered just before and just after training on the task, produce amnesia for the avoidance. Amnesia develops slowly over the first hour and persists for at least 24 h subsequently. If 2-D-gal injections are administered 4 h prior to the training or delayed for 3 h after training, no amnesia occurs. Apart from a brief initial suppression of pecking following injection there are no effects of 2-D-gal on other observed behaviors of the birds. Within the first hour this dose of 2-D-gal inhibits [3H]fucose incorporation into acid-insoluble material by 26% (or 68%, calculated relative to free pool fucose). The amnestic effect of 2-D-gal is not shown by galactose, glucose, fucose, or 2-D-glucose. Injecting 40 mumole of galactose simultaneously with the 2-D-gal abolishes the 2-D-gal-induced amnesia; 40 mumole of fucose, however, does not abolish the amnesia. The utility of 2-D-gal as an agent for analyzing the role of glycoproteins in memory formation is discussed.

Synaptic vesicle proteins and acetylcholine levels in chick forebrain nuclei are altered by passive avoidance training

In a search for biochemical markers of modified synaptic function following training of day-old chicks on a passive avoidance task, we have assayed two monoclonal antibodies to synaptic vesicle proteins (anti-p65 and anti-SV2) and one raised to postsynaptic densities (411B). We have also measured total acetylcholine (ACh) content. Measurements were made on three forebrain regions known to show metabolic and morphological change consequent on training--the lobus parolfactorius (LPO), paleostriatum augmentatum (PA), and medial hyperstriatum ventrale (MHV)--in the right and left hemispheres 2 and 24 h after training chicks on a passive avoidance task, in which they learn to avoid pecking a bead coated with methylanthranilate [methylanthranilate-trained (M-trained)]. Control chicks were trained on a water-coated bead [water-trained (W-trained)]. Twenty-four hours after training, 411B levels showed no differences between W-trained and M-trained chicks in any region. M-training reduced the titre of anti-p65 by 16% in the left PA and 15% in the left MHV and that of anti-SV2 by 19% in the left PA. M-trained chicks showed reduced total ACh content in the LPO by up to 40% and in the PA by up to 48% but had no change in ACh level in the MHV. The decreases in antibody titre were not seen in forebrains analysed 2 h after training, but tendencies toward increases in levels in the right PA and MHV were observed with all three antibodies. Significant differences between right and left hemispheric regions, independent of training, were observed for all the antibodies and for ACh content.(ABSTRACT TRUNCATED AT 250 WORDS)

Lasting changes in spontaneous multi-unit activity in the chick brain following passive avoidance training

Day-old chicks were trained on a one-trial passive avoidance task by pecking at a small, shiny bead coated with either a bitter-tasting substance (methylanthranilate) or water. The undifferentiated spontaneous multi-unit activity recorded bilaterally from anaesthetized chicks 1-13 h after training on the above task exhibited a significant increase in the methylanthranilate-trained over water-control chicks within three structures of the right hemisphere: the hyperstriatum accessorium (47%, P less than 0.05), the medial hyperstriatum ventrale (49.1%, P less than 0.02) and the medial portion of the paleostriatum augmentatum (47.5%, P less than 0.02). Within the multi-unit record obtained from both groups of chicks there were periods of short duration (15-20 ms) containing high-frequency (400-450 Hz) large-amplitude (greater than or equal to 200 microV; 450 microV max peak-to-peak) spikes. As a consequence of training, there was a massive increase in the occurrence of these bursting epochs in the medial hyperstriatum ventrale of both the left (320%, P less than 0.001) and right (350%, P less than 0.001) hemispheres in methylanthranilate-trained compared to water-trained chicks. In addition, the mean number of spikes per burst at this site increased by 66% (P less than 0.001) with no change observed in any other structure sampled. The statistically significant increase in activity within the right hyperstriatum accessorium and medial paleostriatum augmentatum and the non-significant increase in these structures in the left hemisphere was produced almost entirely by tonic spiking. Enhanced spontaneous multi-unit activity recorded under anaesthesia following passive avoidance training in the chick is shown here to be a feature common to several medial forebrain structures. The magnitude of the elevation in bursting frequency and the degree of localization of this effect to the medial hyperstriatum ventrale of methylanthranilate trained chicks would appear to offer strong support to previous biochemical and morphological evidence implicating this structure in the process of memory consolidation for this task. The data reported here represent the first evidence of electrophysiological changes occurring as a consequence of passive avoidance training in the domestic chick.

Incorporation of [3H]fucose in rat hippocampal structures after conditioning by perforant path stimulation and after LTP-producing tetanization

The contribution of glycoprotein synthesis to functional synaptic changes and to the formation of memory traces was investigated by autoradiographic determination of the incorporation of [3H]fucose into the hippocampal structures of rats. In the first experiment, the fucose incorporation was measured after induction of post-tetanic long-term potentiation (LTP) in granular cell synapses by repeated tetanization (200 cps) of the perforant path, and after stimulation of this hippocampal input by the same number of impulses with very low frequency (0.2 cps) not producing LTP. In the second experiment, the incorporation of fucose was determined after an active avoidance training using the stimulation of the perforant path by impulse trains of 15 cps as conditioning stimuli, and after a session of corresponding unpaired stimulations of the perforant path. Unstimulated animals were used in both experiments to measure the basal glycosylation. LTP-producing tetanization resulted only in a slight increase of incorporation into the ipsilateral hippocampal structures without significant differences to similar changes after the corresponding control stimulation with single impulses. After a session of unpaired stimulation of the perforant path with impulse trains of 15 cps only slight and inconsistent changes of incorporation occurred in the hippocampus too. However, after conditioning by the corresponding perforant path stimulation as conditioned stimulus, considerable increases of incorporation were observed in all structures of the ipsilateral hippocampus, when compared to the unpaired control stimulation. An enhanced labeling occurred also in some structures of the contralateral hippocampus mainly receiving commissural inputs. The results suggest again, that the activation of one single hippocampal afferent, even if producing LTP, would not be sufficient to induce an increased glycosylation of neuronal proteins. The increase of glycoprotein formation seems to require the convergence of several inputs, which can be assumed to occur during learning. Therefore, LTP of a single synaptic population seems not to represent the complete long-lasting memory trace, but only one of its components, or a preceding transient storage mechanism.

Inhibition of memory in the chick using a monoclonal anti-Thy-1 antibody

One-day-old chicks trained on a single trial passive avoidance task were administered a monoclonal anti-chick Thy-1 antibody, either intracranially or subcutaneously, at various times before and after learning and retention tested at various times post-learning. This procedure resulted in profound amnesia when anti-Thy-1 antibody was administered immediately before learning (5 min) in the case of the subcutaneous injections or 5 min before until 5 min after the learning process with intracranial injections. Antibody administered at other times, either before or after learning had little or no effect on retention. Retention levels were normal until 50 min post-learning, then declined sharply and remained at control levels for the duration of the test period. Chicks injected with anti-chick cerebellum or anti-rat Thy-1 antibodies showed no evidence of amnesia for the concentration of the antibodies used.

Increased fucosylation of chick brain proteins following training: effects of cycloheximide

When chicks are trained to avoid pecking a bead coated with methylanthranilate in a one-trial passive avoidance task there is an increase in fucose incorporation in vivo and in vitro in the right forebrain base of methylanthranilate (M)-trained compared to water (W)-trained chicks. The relation of this increase to de novo protein synthesis in vivo and in vitro has been examined. Cycloheximide (Cx), 1 mM, inhibited in vitro fucosylation of chick brain slices by 60% after 3 h. However, the training-related increase in in vitro fucosylation still persisted. When Cx was injected intraventricularly 10 min before training, the subsequent increase in in vitro fucosylation due to training was still apparent. When Cx was injected and [14C]leucine and [3H]fucose incorporation studied in vivo in M-trained and W-trained chicks, there was no increase in fucosylation due to training in the Cx-treated M-trained over the W-trained chicks. These results are taken to indicate that in vitro fucosylation and its increase subsequent to training is not protein synthesis-dependent, but that both in vivo and in vitro there are interactions between Cx and fucosylation steps that are independent of Cx's effects on protein synthesis.

Impairment of glycoprotein fucosylation in rat hippocampus and the consequences on memory formation

The intraventricular injection of 2-deoxy-D-galactose led to a dose- and time-dependent decrease in the fucosylation of hippocampal glycoproteins in rats whereas the incorporation of 3H-N-acetyl-glucosamine was not influenced. This effect is not related to an interference with fucose activating or transferring enzymes but can be abolished by an application of D-galactose. Thus, it seems likely that also in brain tissue a deoxy-galactose induced decrease in the fucosylation is due to a hindering of a glycosidic linkage of fucose to the deoxy-sugar incorporated into glycoprotein chains. As a consequence of an intrahippocampal injection of the deoxy-sugar the retention performance of the animals in a foot-shock motivated brightness discrimination task was considerably impaired. But deoxy-galactose is effective only when administered before and immediately after training whereas either a pre- or a post-training injection did not influence the retention performance of the rats. Thus, an effective metabolic inhibition of the glycoprotein completion by the deoxy-sugar starting at the time of training seems to be crucial to interfere with such morphofunctional alterations in the neuronal network underlying the formation of a memory trace.

Isolation of postsynaptic densities from day-old chicken brain

Synaptic plasma membranes from chicken brain were used to isolate a postsynaptic density (PSD) fraction using an aqueous two-phase polymer system and the detergent n-octyl glucoside. The protein and glycoprotein composition and the morphology of the day-old chicken brain PSD fraction were compared with a PSD fraction isolated from 12-week-old chicken brain. The PSD fraction from day-old chicken brain contained predominantly PSDs although, like the fraction from 12-week-old chicken, there was some membrane contamination. The major polypeptides in the day-old chicken fraction resolved by polyacrylamide gel electrophoresis comigrated with alpha- and beta-tubulin (Mr 57,000 and 55,000) and actin (Mr 45,000). The major PSD polypeptide (mPSDp) of 12-week-old chicken forebrain, which has a molecular weight of 52,000 was not a major component in day-old chicken. A polypeptide of molecular weight 63,000 was also far more prominent in the 12-week-old chicken PSD fraction whereas the reverse was true for a polypeptide of 31,000. Day-old chicken brain PSDs contained at least 14 concanavalin A-binding glycoproteins of high (greater than 85,000) molecular weight, the two most prominent having molecular weights of 170,000 and 180,000. In contrast to the polypeptide composition, the glycoprotein pattern of day-old chicken PSDs was very similar to that of the 12-week-old bird. Intraperitoneally injected [3H]fucose was incorporated into the glycoproteins of synaptic plasma membranes and PSDs from day-old chickens.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered colchicine-binding capacity in chick brain regions: relationship to intensity or information content of visual input

The binding of [3H]colchicine to postmitochondrial supernatant fractions of chick brain has been studied, absorbing colchicine-bearing proteins on DEAE-cellulose filter discs. This was assayed at several times after unilateral enucleation of day-old chicks. Binding was unaltered in optic lobes or anterior dorsal forebrain regions contralateral to the removed eye, relative to the corresponding regions contralateral to and thus directly or secondarily innervated by the intact eye. Colchicine binding was also assayed after training chicks to suppress pecking at a metallic bead coated with aversive-tasting methylanthranilate. At 4 but not 24 h after the one-trial training, binding was selectively elevated in the anterior dorsal forebrain roof. Results are taken to imply that alterations in tubulin content of chick brain may reflect stress-related changes, possibly mediated by systemic endocrine flux, rather than a more localized learning experience.

Passive avoidance training increases fucose incorporation into glycoproteins in chick forebrain slices in vitro

When day old chicks are trained to avoid pecking at a bright bead coated with methyl anthranilate, many neurochemical changes, both transient and longer lasting, have been found. These include an increased fucose incorporation in vivo into particulate glycoproteins, which persists for at least 24 hrs after training. We have now developed an in vitro method for studying fucose incorporation and have been able to replicate effects of training found in vivo. Chick forebrain slices incubated at 42 degrees in a glucose containing-medium incorporate L-[U14C]fucose linearly for up to 3 hrs at rates of 30-35 nmol/g prot/hr. Incorporation was only 60% inhibited by cycloheximide indicating that some fucosylation is occurring on pre-existing proteins. Fucose incorporation was compared in slices from trained and control chicks and, as in vivo, a 16% increase in incorporation into the right forebrain base of trained birds was found. This increase was confined to the microsomal fraction. When cycloheximide was added to the incubation medium, the enhanced fucose incorporation in slices from trained birds was still observed.

Effect of passive avoidance training on in vitro protein synthesis in forebrain slices of day-old chicks

Slices from the forebrains of day-old chicks represent a highly active in vitro protein-synthesising system. The in vitro incorporation of L-[14C]leucine into protein of slices was estimated to be 2.5 mmol/mg protein/h. Incorporation was linear over 90 min of incubation and was suppressed by 92% by 1 mM cycloheximide. The highest incorporation was into microsomal and cell-soluble fractions. Under the electron microscope, slices appeared vacuolated near the cut surfaces, but well preserved internally (greater than 40 micron from the edge). Autoradiography showed that radioactivity was incorporated evenly across the slice with no decrease in label in the central part of the tissue. The rate of incorporation was only weakly dependent on leucine concentration in the medium (0.04-1 mM). Addition of a mixture of unlabelled amino acids (1 mM) produced a 20-50% inhibition of incorporation of radioactive L-leucine depending on the amino acids involved. In slices prepared from chicks 1 h after training on a one-trial passive avoidance paradigm, L-[14C]leucine incorporation was 23% higher (p less than 0.01) in the forebrain roof than in slices from control chicks. This figure is comparable to the one previously reported in vivo. Subcellular fractionation of incubated slices from the forebrain roof of trained and control birds revealed that the increased protein synthesis was due mainly to an elevated leucine incorporation into the soluble fraction.

Training increases [3H]fucose incorporation in chick brain only if followed by memory storage

Incorporation of [3H]fucose into glycoproteins is increased in the forebrain base and anterior forebrain roof of day-old chicks following passive avoidance training. In chicks trained but rendered apparently amnestic by immediate transcranial electroshock, the increased incorporation by comparison with untrained-shocked birds was abolished. If the electroshock was delayed by 10 min, the chicks showed recall for the task and fucose incorporation was increased by comparison with untrained but shocked or trained and immediate-shocked birds. We conclude that the increased incorporation of [3H]fucose is not a result of any concomitant of training but is directly associated with engram formation.

Hemispheric asymmetry of synapses in chick medial hyperstriatum ventrale following passive avoidance training: a stereological investigation

A stereological analysis was made of synapses in the left and right hemispheres of chick medial hyperstriatum ventrale (MHV) 24h after passive avoidance training (PAL) and in water trained controls (W-control). The synaptic parameters examined were (D), the mean length of the postsynaptic thickening; (NV.syn), the number of synapses per unit volume of neuropil; (VV.syn), the volume density of the pre-synaptic bouton; (NV.ves), the number of synaptic vesicles per unit volume of neuropil and (ves.syn), the mean number of synaptic vesicles per pre-synaptic bouton. No significant differences exist in NV.syn between the left or right hemispheres of W-control and trained chicks, nor is NV.syn influenced by training. However, in W-control chicks D in the right MHV is significantly greater (12%) than in the left MHV and this difference disappears on training. There are no differences in VV.syn between left and right hemispheres of W-control chicks but following training VV.syn is 22.7% greater in the left MHV than in the right MHV. Training als influences the number of synaptic vesicles; in W-control chicks NV.ves in the right MHV is 12.25% greater than in the left MHV but following training these differences are reversed. When the data are expressed as numbers of vesicles per synapse (ves.syn), values for the left hemisphere of trained chicks exceed those in the right hemisphere by a staggering 61.38%. These results are discussed in the context of biochemical and electrophysiological studies which suggest that there is lateralization of the memory trace.

Passive avoidance training increases fucokinase activity in right forebrain base of day-old chicks

Fucokinase (EC 2.7.1.52) activity was estimated in supernatants of homogenate from day-old chick forebrain. Enzyme kinetic studies gave a Km of 4.5 X 10(-6) M and Vmax of 3.72 nmol fucose converted into fucose-1-phosphate/mg prot/h. The pH optimum was 7.5. The enzyme is thus considerably more active than was reported for other species and tissues. There were no differences in enzyme activity between the four forebrain regions studied. One hour after chicks were trained on a one-trial passive avoidance learning paradigm, enzyme activity in the right forebrain base increased 14% over control values (p less than 0.02). The 11.3% increase in activity in the left forebrain base and 10.3% increase in the left roof were not statistically significant. The relationship of this change to the increased fucose incorporation into glycoproteins known to occur over a similar time period and the significance of the lateralization of the increase are discussed.

Inhibition of long-term memory formation in the chicken by anti chick Thy-1 antibody

Anti-chick Thy-1 antibodies administered close to a single trial passive avoidance learning task in day-old chicks resulted in inhibition of long-term memory formation. The retention time course was comparable to that obtained with the protein synthesis inhibitor anisomycin. The amnestic effect of the anti-chick Thy-1 antibody appears to be mediated solely by immunoglobulin G, and is species specific since anti-rat Thy-1 antibodies did not produce amnesia. The results are consistent with a three stage model of memory formation, suggest a role for glycoproteins in long term memory formation, and emphasise the potential of neuroimmunological tools for investigating the neurological bases of memory formation.

Ontogenetic and imprinting-induced changes in chick brain protein metabolism and muscarinic receptor binding activity

Over the 20-min period following exposure of young chicks to a flashing light as an imprinting stimulus there is an increased incorporation of [14C]leucine into an acidic (tubulin-enriched) protein fraction of the anterior dorsal forebrain in birds which have learnt the characteristics of the stimulus as compared with, either birds which have been exposed to an imprinting stimulus but learn poorly, or chicks kept in the dark. This brain region has been implicated in several studies as the locus for a number of biochemical modulations that accompany learning. The amount of [14C]leucine incorporated does not seem to be determined by precursor pool availability; it does, however, correlate with a well-validated measure of the extent to which birds have learnt to recognise the characteristics of the stimulus, as shown by a two-choice discrimination test. There is no change in the total content of tubulin dimer as assayed by colchicine binding under these conditions. Additionally, in birds which show evidence of learning, the binding of quinuclidinyl benzilate, an irreversible muscarinic ligand, is altered in both the posterior dorsal forebrain and midbrain regions. None of these effects could be simply the result of visual stimulation. The meaning of these changes is discussed.

Subcellular localization of increased incorporation of [3H]fucose following passive avoidance learning in the chick

The effect of training on a passive avoidance test on incorporation of [3H]fucose into subcellular fractions of the anterior forebrain roof of 1-day-old chicks was determined. Isotope was injected intraperitoneally, and birds tested and killed after 3 h. There was an increase in incorporation in trained compared with untrained control birds in the synaptic membrane (19% elevation, P less than 0.02) and the mitochondrial (14% elevation, P less than 0.05) fractions. Following intracranial injection, increased incorporation in trained birds was seen only in the synaptic membrane fraction (39% elevation, P less than 0.01); this increase in incorporation was not limited to any particular electrophoretically separated glycopeptides, but occurred in all 9 detected peaks.