Intra-amygdala injections of CREB antisense impair inhibitory avoidance memory: role of norepinephrine and acetylcholine

Fus1 KO Mouse As a Model of Oxidative Stress-Mediated Sporadic Alzheimer's Disease: Circadian Disruption and Long-Term Spatial and Olfactory Memory Impairments

Insufficient advances in the development of effective therapeutic treatments of sporadic Alzheimer's Disease (sAD) to date are largely due to the lack of sAD-relevant animal models. While the vast majority of models do recapitulate AD's hallmarks of plaques and tangles by virtue of tau and/or beta amyloid overexpression, these models do not reflect the fact that in sAD (unlike familial AD) these genes are not risk factors per se and that other mechanisms like oxidative stress, metabolic dysregulation and inflammation play key roles in AD etiology. Here we characterize and propose the Fus1 KO mice that lack a mitochondrial protein Fus1/Tusc2 as a new sAD model. To establish sAD relevance, we assessed sAD related deficits in Fus1 KO and WT adult mice of 4-5 months old, the equivalent human age when the earliest cognitive and olfactory sAD symptoms arise. Fus1 KO mice showed oxidative stress (increased levels of ROS, decreased levels of PRDX1), disruption of metabolic homeostasis (decreased levels of ACC2, increased phosphorylation of AMPK), autophagy (decreased levels of LC3-II), PKC (decreased levels of RACK1) and calcium signaling (decreased levels of Calb2) in the olfactory bulb and/or hippocampus. Mice were behaviorally tested using objective and accurate video tracking (Noldus), in which Fus1 KO mice showed clear deficits in olfactory memory (decreased habituation/cross-habituation in the short and long term), olfactory guided navigation memory (inability to reduce their latency to find the hidden cookie), spatial memory (learning impairments on finding the platform in the Morris water maze) and showed more sleep time during the diurnal cycle. Fus1 KO mice did not show clear deficits in olfactory perception (cross-habituation), association memory (passive avoidance) or in species-typical behavior (nest building) and no increased anxiety (open field, light-dark box) or depression/anhedonia (sucrose preference) at this relatively young age. These neurobehavioral deficits of the Fus1 KO mice at this relatively young age are highly relevant to sAD, making them suitable for effective research on pharmacological targets in the context of early intervention of sAD.

Identification and Characterization of the V(D)J Recombination Activating Gene 1 in Long-Term Memory of Context Fear Conditioning

An increasing body of evidence suggests that mechanisms related to the introduction and repair of DNA double strand breaks (DSBs) may be associated with long-term memory (LTM) processes. Previous studies from our group suggested that factors known to function in DNA recombination/repair machineries, such as DNA ligases, polymerases, and DNA endonucleases, play a role in LTM. Here we report data using C57BL/6 mice showing that the V(D)J recombination-activating gene 1 (RAG1), which encodes a factor that introduces DSBs in immunoglobulin and T-cell receptor genes, is induced in the amygdala, but not in the hippocampus, after context fear conditioning. Amygdalar induction of RAG1 mRNA, measured by real-time PCR, was not observed in context-only or shock-only controls, suggesting that the context fear conditioning response is related to associative learning processes. Furthermore, double immunofluorescence studies demonstrated the neuronal localization of RAG1 protein in amygdalar sections prepared after perfusion and fixation. In functional studies, intra-amygdalar injections of RAG1 gapmer antisense oligonucleotides, given 1 h prior to conditioning, resulted in amygdalar knockdown of RAG1 mRNA and a significant impairment in LTM, tested 24 h after training. Overall, these findings suggest that the V(D)J recombination-activating gene 1, RAG1, may play a role in LTM consolidation.

Fluorocitrate induced the alterations of memory-related proteins and tau hyperphosphorylation in SD rats

Astrocytes provide structural, metabolic and trophic supports for neurons. However, there are no direct evidences whether astrocytes involve in the regulation of synaptic proteins expression and tau phosphorylation until now. Here, we injected 1 nmol fluorocitrate (FC), which preferentially taken up by astrocytes and results in reversible inhibition of the astrocytic tricarboxylic acid cycle, into the left lateral ventricle of the brain in the SD rats for 1h, and found that FC treatment decreased several memory-related proteins levels, such as AMPA receptor GluR1/2, postsynaptic density protein 93/95, Arc and phosphorylated cAMP response element binding proteins, while increased synaptophysin and synapsin I levels in the hippocampus. FC treatment also increased the levels of phosphorylated tau at multiple Alzheimer-related phosphorylation sites, as well as activation of glycogen synthase kinase-3β and inactivation of protein phosphatase-2A. Similar effects were also observed in the primary hippocampal neurons, which were cultured with the conditioned media from FC-treatment primary astrocytes. Our data suggest that astrocytes regulate neuronal tau phosphorylation and several synaptic proteins expression.

Properties and mechanisms of olfactory learning and memory

Memories are dynamic physical phenomena with psychometric forms as well as characteristic timescales. Most of our understanding of the cellular mechanisms underlying the neurophysiology of memory, however, derives from one-trial learning paradigms that, while powerful, do not fully embody the gradual, representational, and statistical aspects of cumulative learning. The early olfactory system—particularly olfactory bulb—comprises a reasonably well-understood and experimentally accessible neuronal network with intrinsic plasticity that underlies both one-trial (adult aversive, neonatal) and cumulative (adult appetitive) odor learning. These olfactory circuits employ many of the same molecular and structural mechanisms of memory as, for example, hippocampal circuits following inhibitory avoidance conditioning, but the temporal sequences of post-conditioning molecular events are likely to differ owing to the need to incorporate new information from ongoing learning events into the evolving memory trace. Moreover, the shapes of acquired odor representations, and their gradual transformation over the course of cumulative learning, also can be directly measured, adding an additional representational dimension to the traditional metrics of memory strength and persistence. In this review, we describe some established molecular and structural mechanisms of memory with a focus on the timecourses of post-conditioning molecular processes. We describe the properties of odor learning intrinsic to the olfactory bulb and review the utility of the olfactory system of adult rodents as a memory system in which to study the cellular mechanisms of cumulative learning.

Differential activation of amygdala Arc expression by positive and negatively valenced emotional learning conditions

Norepinephrine is released in the amygdala following negatively arousing learning conditions. This event initiates a cascade of changes including the transcription of activity-regulated cytoskeleton-associated protein (Arc) expression, an early-immediate gene associated with memory encoding. Recent evidence suggests that the valence of emotionally laden encounters may generate lateralized, as opposed to symmetric release of this transmitter in the right or left amygdala. It is currently not clear if valence-induced patterns of selective norepinephrine output across hemispheres are also reproduced in downstream pathways of cellular signaling necessary for memory formation. This question was addressed by determining if Arc expression is differentially distributed across the right and left amygdala following exposure to positively or negatively valenced learning conditions respectively. Male Sprague Dawley rats were randomly assigned to groups exposed to the Homecage only, five auditory tones only, or five auditory tones paired with footshock (0.35 mA) during Pavlovian fear conditioning. Western blot analysis revealed that Arc expression in the right amygdala was elevated significantly above that observed in the left amygdala 60 and 90 min following fear conditioning. Similarly, subjects exposed to a negatively valenced outcome consisting of an unexpected reduction in food rewards showed a greater level of Arc expression in only the right, but not left basolateral amygdala. Presenting a positively valenced event involving an unexpected increase in food reward magnitude following bar pressing, resulted in significantly greater Arc expression in the left, but not right basolateral amygdala (p < 0.01). These findings indicate that the valence of emotionally arousing learning conditions is reflected at later stages of synaptic plasticity involving the transcription of immediate early genes such as Arc.

A novel brain penetrant NPS receptor antagonist, NCGC00185684, blocks alcohol-induced ERK-phosphorylation in the central amygdala and decreases operant alcohol self-administration in rats

The Neuropeptide S receptor, a Gs/Gq-coupled GPCR expressed in brain regions involved in mediating drug reward, has recently emerged as a candidate therapeutic target in addictive disorders. Here, we describe the in vitro and in vivo pharmacology of a novel, selective and brain penetrant NPSR antagonist with nanomolar affinity for the NPSR, NCGC00185684. In vitro, NCGC00185684 shows biased antagonist properties, and preferentially blocks ERK-phosphorylation over intracellular cAMP or calcium responses to NPS. In vivo, systemic NCGC00185684 blocks alcohol-induced ERK-phosphorylation in the rat central amygdala, a region involved in regulation of alcohol intake. NCGC00185684 also decreases operant alcohol self-administration, and lowers motivation for alcohol reward as measured using progressive ratio responding. These effects are behaviorally specific, in that they are observed at doses that do not influence locomotor activity or reinstatement responding following extinction. Together, these data provide an initial validation of the NPSR as a therapeutic target in alcoholism.

Event-related functional magnetic resonance imaging of a low dose of dexmedetomidine that impairs long-term memory

BACKGROUND

Work suggests the amnesia from dexmedetomidine (an α2-adrenergic agonist) is caused by a failure of information to be encoded into long-term memory and that dexmedetomidine might differentially affect memory for emotionally arousing material. We investigated these issues in humans using event-related neuroimaging to reveal alterations in brain activity and subsequent memory effects associated with drug exposure.

METHODS

Forty-eight healthy volunteers received a computer-controlled infusion of either placebo or low-dose dexmedetomidine (target = 0.15 ng/ml plasma) during neuroimaging while they viewed and rated 80 emotionally arousing (e.g., graphic war wound) and 80 nonarousing neutral (e.g., cup) pictures for emotional arousal content. Long-term picture memory was tested 4 days later without neuroimaging. Imaging data were analyzed for drug effects, emotional processing differences, and memory-related changes with statistical parametric mapping-8.

RESULTS

Dexmedetomidine impaired overall (mean ± SEM) picture memory (placebo: 0.58 ± 0.03 vs. dexmedetomidine: 0.45 ± 0.03, P = 0.001), but did not differentially modulate memory as a function of item arousal. Arousing pictures were better remembered for both groups. Dexmedetomidine had regionally heterogeneous effects on brain activity, primarily decreasing it in the cortex and increasing it in thalamic and posterior hippocampal regions. Nevertheless, a single subsequent memory effect for item memory common to both groups was identified only in the left hippocampus/amygdala. Much of this effect was found to be larger for the placebo than dexmedetomidine group.

CONCLUSION

Dexmedetomidine impaired long-term picture memory, but did not disproportionately block memory for emotionally arousing items. The memory impairment on dexmedetomidine corresponds with a weakened hippocampal subsequent memory effect.

Epinephrine and glucose modulate training-related CREB phosphorylation in old rats: relationships to age-related memory impairments

Epinephrine enhances memory in young adult rats, in part, by increasing blood glucose levels needed to modulate memory. In old rats, epinephrine is deficient at raising blood glucose levels and thus is only moderately effective at enhancing memory. In contrast, systemic glucose injections improve memory in old rats, with resulting memory performance equal to that of young rats. The diminished response of glucose to training in old rats may blunt downstream neurochemical and molecular mechanisms needed to upregulate memory processes. In the first experiment, young adult and old rats were trained on an inhibitory avoidance task with immediate post-training injections of aCSF or glucose into the dorsal hippocampus. Old rats had significant memory impairments compared to young rats 7 days after training. Intrahippocampal injections of glucose reversed age-related deficits, improving memory scores in old rats to values seen in young rats. A second experiment examined age-related changes in activation of the transcription factor CREB, which is widely implicated in memory formation and may act downstream of hormonal and metabolic signals. Activation was assessed in response to training with systemic injections of epinephrine and glucose at doses known to enhance memory. Young adult and old rats were trained on inhibitory avoidance with immediate post-training systemic injections of saline, epinephrine, or glucose. After training, old rats had significant impairments in CREB phosphorylation in area CA1 and the dentate gyrus region of the hippocampus, and in the basolateral and lateral amygdala. Epinephrine and glucose attenuated age-related deficits in CREB phosphorylation, but were more effective in the amygdala and hippocampus, respectively. Together, these results support the view that age-related changes in blood glucose responses to epinephrine contribute to memory impairments, which may be related to alterations in regional patterns of CREB phosphorylation.

Cycloheximide impairs and enhances memory depending on dose and footshock intensity

This experiment examined the effects on memory of interactions of cycloheximide dose and training foot shock intensity. Mice received injections of cycloheximide (120 mg/kg, s.c.) or saline 30 min prior to inhibitory avoidance training with shock intensities of 100, 150, 250 or 300 μA (1 s duration). Memory was tested 48 h later. The saline control mice showed increasing memory latencies as a function of shock intensity. The ability of cycloheximide to impair memory increased as the training shock intensity increased. In a second experiment, mice were trained with a 200 μA (1 s duration) shock and received injections of saline or cycloheximide at one of several doses (30, 60 or 120 mg/kg). Under these training conditions, cycloheximide enhanced memory in an inverted-U dose-response manner. These findings are consistent with prior findings suggesting that protein synthesis inhibitors act on memory by altering modulators of memory formation as a secondary consequence of the inhibition of protein synthesis rather than by interfering with training-initiated synthesis of proteins required for memory formation.

Age-related impairments in memory and in CREB and pCREB expression in hippocampus and amygdala following inhibitory avoidance training

This experiment examined whether age-related changes in CREB and pCREB contribute to the rapid forgetting seen in aged animals. Young (3-month-old) and aged (24-month-old) Fischer-344 rats received inhibitory avoidance training with a low (0.2 mA, 0.4 s) or moderate (0.5 mA, 0.5 s) foot shock; memory was measured 7 days later. Other rats were euthanized 30 min after training, and CREB and pCREB expression levels were examined in the hippocampus, amygdala, and piriform cortex using immunohistochemistry. CREB levels decreased with age in the hippocampus and amygdala. After training with either shock level, young rats exhibited good memory and increases in pCREB levels in the hippocampus and amygdala. Aged rats exhibited good memory for the moderate but not the low shock but did not show increases in pCREB levels after either shock intensity. These results suggest that decreases in total CREB and in pCREB activation in the hippocampus and amygdala may contribute to rapid forgetting in aged rats. After moderate foot shock, the stable memory in old rats together with absence of CREB activation suggests either that CREB was phosphorylated in a spatiotemporal pattern other than analyzed here or that the stronger training conditions engaged alternate mechanisms that promote long-lasting memory.

Donepezil attenuates hippocampal neuronal damage and cognitive deficits after global cerebral ischemia in gerbils

Decreased cerebral blood flow causes cognitive impairments and neuronal injury in vascular dementia. In the present study, we reported that donepezil, a cholinesterase inhibitor, improved transient global cerebral ischemia-induced spatial memory impairment in gerbils. Treatment with 5mg/kg of donepezil for 21 consecutive days following a 10-min period of ischemia significantly inhibited delayed neuronal death in the hippocampal CA1 region. In Morris water maze test, memory impairment was significantly improved by donepezil treatment. Western blot analysis showed that donepezil treatment prevented reductions in p-CaMKII and p-CREB protein levels in the hippocampus. These results suggest that donepezil attenuates the memory deficit induced by transient global cerebral ischemia and this neuroprotection may be associated with the phosphorylation of CaMKII and CERB in the hippocampus.

Lidocaine attenuates anisomycin-induced amnesia and release of norepinephrine in the amygdala

When administered near the time of training, protein synthesis inhibitors such as anisomycin impair later memory. A common interpretation of these findings is that memory consolidation requires new protein synthesis initiated by training. However, recent findings support an alternative interpretation that abnormally large increases in neurotransmitter release after injections of anisomycin may be responsible for producing amnesia. In the present study, a local anesthetic was administered prior to anisomycin injections in an attempt to mitigate neurotransmitter actions and thereby attenuate the resulting amnesia. Rats received lidocaine and anisomycin injections into the amygdala 130 and 120 min, respectively, prior to inhibitory avoidance training. Memory tests 48 h later revealed that lidocaine attenuated anisomycin-induced amnesia. In other rats, in vivo microdialysis was performed at the site of amygdala infusion of lidocaine and anisomycin. As seen previously, anisomycin injections produced large increases in release of norepinephrine in the amygdala. Lidocaine attenuated the anisomycin-induced increase in release of norepinephrine but did not reverse anisomycin inhibition of protein synthesis, as assessed by c-Fos immunohistochemistry. These findings are consistent with past evidence suggesting that anisomycin causes amnesia by initiating abnormal release of neurotransmitters in response to the inhibition of protein synthesis.

Memory for reward location is enhanced even though acetylcholine efflux within the amygdala is impaired in rats with damage to the diencephalon produced by thiamine deficiency

A rodent model of diencephalic amnesia produced by thiamine deficiency (pyrithiamine-induced thiamine deficiency [PTD]) was implemented to assess both changes in behavior and acetylcholine (ACh) efflux in the amygdala across four training sessions of a delayed alternation task. Two versions of the delayed alternation task were used. In one version, when a correct alternation was made a unique reward was paired with each spatial location ([left arm-chocolate milk] or [right arm-rat chow]). This paradigm is called the differential outcomes procedure (DOP). In the second version of the task, correct delayed alternation resulted in the same rewards but randomized across location (Nondifferential Outcomes Procedure [NOP]). The PTD rats were impaired on the first session of delayed alternation testing. However, both control and PTD rats using the DOP performed significantly better on delayed alternation than rats trained with the NOP.This effect was driven primarily by the PTD rats in the DOP condition outperforming all other groups on sessions 2-4. Although ACh efflux in the amygdala increased during delayed alternation testing in all groups, the NOP-trained rats had a greater rise in training-related ACh release in the post-training period. This suggests that increased amygdalar cholinergic activation is more critical for processing spatial information than episodic reward information. These data correspond with the idea that cholinergic activation of the amygdala promotes processing in other neural systems.

Phenylbutyric acid prevents rats from electroconvulsion-induced memory deficit with alterations of memory-related proteins and tau hyperphosphorylation

Electroconvulsive therapy has been commonly applied in the treatment of refractory depression, but its cognitive side effects are noticed and restrict its application. The molecular mechanisms underlying the side effects remain elusive, and there is no efficient prevention. By employing a recognized electroconvulsive shock (ECS) rat model, we found in the present study that ECS induced spatial memory deficits with simultaneous decreases in synaptic proteins of N-methyl-D-aspartate receptor 2A/B (NR2A/B) and postsynaptic density 95 (PSD95), the immediate early gene c-Fos and cAMP response element binding (CREB) proteins, all of which are memory-related proteins. ECS also caused tau hyperphosphorylation at multiple Alzheimer-related phosphorylation sites with activation of glycogen synthase kinase-3beta (GSK-3beta), Akt and phospho-PKR-like endoreticulum (PERK), and inhibition of protein phosphatase-2A (PP)-2A. Intraperitoneal injection of phenylbutyric acid (PBA), an aromatic short chain fatty acid with the functions of molecule chaperon, prevented rats from the ECS-induced memory deficits, alterations of the memory-associated proteins, and tau hyperphosphorylation. Our data suggest that PBA may be potentially used for attenuating the side effects caused by electroconvulsive therapy.

Intrahippocampal infusions of anisomycin produce amnesia: contribution of increased release of norepinephrine, dopamine, and acetylcholine

Intra-amygdala injections of anisomycin produce large increases in the release of norepinephrine (NE), dopamine (DA), and serotonin in the amygdala. Pretreatment with intra-amygdala injections of the beta-adrenergic receptor antagonist propranolol attenuates anisomycin-induced amnesia without reversing the inhibition of protein synthesis, and injections of NE alone produce amnesia. These findings suggest that abnormal neurotransmitter responses may be the basis for amnesia produced by inhibition of protein synthesis. The present experiment extends these findings to the hippocampus and adds acetylcholine (ACh) to the list of neurotransmitters affected by anisomycin. Using in vivo microdialysis at the site of injection, release of NE, DA, and ACh was measured before and after injections of anisomycin into the hippocampus. Anisomycin impaired inhibitory avoidance memory when rats were tested 48 h after training and also produced substantial increases in local release of NE, DA, and ACh. In an additional experiment, pretreatment with intrahippocampal injections of propranolol prior to anisomycin and training significantly attenuated anisomycin-induced amnesia. The disruption of neurotransmitter release patterns at the site of injection appears to contribute significantly to the mechanisms underlying amnesia produced by protein synthesis inhibitors, calling into question the dominant interpretation that the amnesia reflects loss of training-initiated protein synthesis necessary for memory formation. Instead, the findings suggest that proteins needed for memory formation are available prior to an experience, and that post-translational modifications of these proteins may be sufficient to enable the formation of new memories.

Nicotinic receptor-evoked hippocampal norepinephrine release is highly sensitive to inhibition by isoflurane

BACKGROUND

Inhaled anaesthetics (IAs) produce multiple dose-dependent behavioural effects including amnesia, hypnosis, and immobility in response to painful stimuli that are mediated by distinct anatomical, cellular, and molecular mechanisms. Amnesia is produced at lower anaesthetic concentrations compared with hypnosis or immobility. Nicotinic acetylcholine receptors (nAChRs) modulate hippocampal neural network correlates of memory and are highly sensitive to IAs. Activation of hippocampal nAChRs stimulates the release of norepinephrine (NE), a neurotransmitter implicated in modulating hippocampal synaptic plasticity. We tested the hypothesis that IAs disrupt hippocampal synaptic mechanisms critical to memory by determining the effects of isoflurane on NE release from hippocampal nerve terminals.

METHODS

Isolated nerve terminals prepared from adult male Sprague-Dawley rat hippocampus were radiolabelled with [(3)H]NE and either [(14)C]GABA or [(14)C]glutamate and superfused at 37 degrees C. Release evoked by a 2 min pulse of 100 microM nicotine or 5 microM 4-aminopyridine was evaluated in the presence or absence of isoflurane and/or selective antagonists.

RESULTS

Nicotine-evoked NE release from rat hippocampal nerve terminals was nAChR- and Ca(2+)-dependent, involved both alpha7 and non-alpha7 subunit-containing nAChRs, and was partially dependent on voltage-gated Na(+) channel activation based on sensitivities to various antagonists. Isoflurane inhibited nicotine-evoked NE release (IC(50)=0.18 mM) more potently than depolarization-evoked NE release (IC(50)=0.27 mM, P=0.014), consistent with distinct presynaptic mechanisms of IA action.

CONCLUSIONS

Inhibition of hippocampal nAChR-dependent NE release by subanaesthetic concentrations of isoflurane supports a role in IA-induced amnesia.