Reduced Hippocampal Neurogenesis in Mice Deficient in Apoptosis Repressor with Caspase Recruitment Domain (ARC).

In the adult hippocampal dentate gyrus (DG), the majority of newly generated cells are eliminated by apoptotic mechanisms. The apoptosis repressor with caspase recruitment domain (ARC), encoded by the Nol3 gene, is a potent and multifunctional death repressor that inhibits both death receptor and mitochondrial apoptotic signaling. The aim of the present study was to parse the role of ARC in the development of new granule cell neurons. Nol3 gene expression as revealed by in situ hybridization is present in the entire dentate granule cell layer. Moreover, a comparison of Nol3 expression between FACS-sorted Sox2-positive neural stem cells and Doublecortin (DCX)-positive immature neurons demonstrates upregulation of Nol3 during neurogenesis. Using ARC-deficient mice, we show that proliferation and survival of BrdU birth-dated cells are strongly reduced in the absence of ARC while neuronal-glial fate choice is not affected. Both the number of DCX-positive cells and the number of calretinin (CR)-positive immature postmitotic neurons are reduced in the hippocampus of ARC-/- mice. ARC knockout is not associated with increased numbers of microglia or with microglia activation. However, hippocampal brain-derived neurotrophic factor (BDNF) protein content is significantly increased in ARC-/- mice, possibly representing a compensatory response. Collectively, our results suggest that ARC plays a critical cell-autonomous role in preventing cell death during adult granule cell neogenesis.

Developmental Exposure to Psychostimulant Primes Activity-dependent Gene Induction in Frontal Cortex.

Perinatal neurodevelopment involves extensive formation of neural connections and onset of activity-dependent gene expression for synaptic function and plasticity. Exposure to psychostimulants at this stage imposes significant risks for developing cognitive and affective disorders later in life. However, how developmental exposure to psychostimulants may induce long-lasting molecular changes relevant to neural circuit function remains incompletely understood. In this study, we investigated the impacts of psychostimulant amphetamine on the activity-dependent induction of synaptic adaptor molecule Arc in the frontal cortex of neonatal mice. We found that transient exposure to amphetamine not only amplifies activity-dependent Arc mRNA expression immediately, but also potentiates subsequent induction of Arc mRNA in the absence of amphetamine. This priming effect is associated with a rapid and persistent increase in histone mono-methylation (H3K4me1), a marker for transcriptionally permissive chromatin, at the Arc locus, but not any long-lasting change in the phosphorylation of upstream transcription factor CREB. Furthermore, the increase in H3K4me1 at the Arc locus requires dopamine receptor signaling, and the priming of Arc expression correlates with the dopaminergic innervation pattern in the frontal cortex. Together, our results demonstrate that developmental exposure to psychostimulant amphetamine induces long-lasting chromatin changes and primes activity-dependent Arc gene induction. These findings reveal the molecular targets of psychostimulant during perinatal development that may contribute to long-term psychiatric risks.

Differential fear conditioning generates prefrontal neural ensembles of safety signals.

Fear discrimination is critical for survival, while fear generalization is effective for avoiding dangerous situations. Overgeneralized fear is a typical symptom of anxiety disorders, including generalized anxiety disorder and posttraumatic stress disorder (PTSD). Previous research demonstrated that fear discrimination learning is mediated by prefrontal mechanisms. While the prelimbic (PL) and infralimbic (IL) subdivisions of the medial prefrontal cortex (mPFC) are recognized for their excitatory and inhibitory effects on the fear circuit, respectively, the mechanisms driving fear discrimination are unidentified. To obtain insight into the mechanisms underlying context-specific fear discrimination, we investigated prefrontal neuronal ensembles representing distinct experiences associated with learning to disambiguate between dangerous and similar, but not identical, harmless stimuli. Here, we show distinct quantitative activation differences in response to conditioned and generalized fear experiences, as well as modulation of the neuronal ensembles associated with successful acquisition of context-safety contingencies. These findings suggest that prefrontal neuronal ensembles patterns code functional context-danger and context-safety relationships. The PL subdivision of the mPFC monitors context-danger associations to conditioned fear, whereas differential conditioning sparks additional ensembles associated with the inhibition of generalized fear in both the PL and IL subdivisions of the mPFC. Our data suggest that fear discrimination learning is associated with the modulation of prefrontal subpopulations in a subregion- and experience-specific fashion, and the learning of appropriate responses to conditioned and initially generalized fear experiences is driven by gradual updating and rebalancing of the prefrontal memory representations.

Distinct regulation pattern of Egr-1, BDNF and Arc during morphine-withdrawal conditioned place aversion paradigm: Role of glucocorticoids.

Negative affective aspects of opiate abstinence contribute to the persistence of substance abuse. Importantly, interconnected brain areas involved in aversive motivational processes, such as the ventral tegmental area (VTA) and medial prefrontal cortex (mPFC), become activated when animals are confined to withdrawal-paired environments. In the present study, place aversion was elicited in sham and adrenalectomized (ADX) animals by conditioned naloxone-precipitated drug withdrawal following exposure to chronic morphine. qPCR was employed to detect the expression of brain derived neurotrophic factor (Bdnf) and the immediate early genes (IEG) early growth response 1 (Egr-1) and activity-regulated cytoskeletal-associated protein (Arc) mRNAs in the VTA and mPFC at different time points of the conditioned place aversion (CPA) paradigm: after the conditioning phase and after the test phase. Sham + morphine rats exhibited robust CPA, which was impaired in ADX + morphine animals. Egr-1 and Arc were induced in the VTA and mPFC after morphine-withdrawal conditioning phase. Furthermore, Bdnf expression was enhanced in the VTA during the test phase. Bdnf induction seemed to be glucocorticoid-dependent, given that was correlated with HPA axis function and was not observed in morphine-dependent ADX animals. In addition, BDNF regulation and function was opposite in the VTA and mPFC during aversive-withdrawal memory retrieval. Our results suggest that IEGs and BDNF in these brain regions may play key roles in mediating the negative motivational component of opiate withdrawal.

Nucleus reuniens of the thalamus controls fear memory intensity, specificity and long-term maintenance during consolidation.

The thalamic nucleus reuniens (NR) has been shown to support bidirectional medial prefrontal cortex-hippocampus communication and synchronization relevant for cognitive processing. Using non-selective or prolonged inactivation of the NR, previous studies reported its activity positively modulates aversive memory consolidation. Here we examined the NR's role in consolidating contextual fear memories with varied strength, at both recent and more remote time points, using muscimol-induced temporary inactivation in rats. Results indicate the NR negatively modulates fear memory intensity, specificity, and long-term maintenance. The more intense, generalized, and enduring fear memory induced by NR inactivation during consolidation was less prone to behavioral suppression by extinction or reconsolidation disruption induced by clonidine, an alpha-2 adrenergic receptor agonist. Lastly, we used immunohistochemistry for Arc protein, which is involved in synaptic modifications underlying memory consolidation, to investigate whether treatment condition and/or conditioning status could change its levels not only in the NR, but also in the hippocampus (dorsal and ventral CA1 subregions) and the medial prefrontal cortex (anterior cingulate, prelimbic and infralimbic subregions). Results indicate a significant imbalance in the number of Arc-expressing neurons in the brain areas investigated in muscimol fear conditioned animals when compared with controls. Collectively, present results provide convergent evidence for the NR's role as a hub regulating quantitative and qualitative aspects of a contextual fear memory during its consolidation that seem to influence the subsequent susceptibility to experimental interventions aiming at attenuating its expression. They also indicate the selectivity and duration of a given inactivation approach may influence its outcomes.

Optimization of immunolabeling and clearing techniques for indelibly labeled memory traces.

Recent genetic tools have allowed researchers to visualize and manipulate memory traces (i.e., engrams) in small brain regions. However, the ultimate goal is to visualize memory traces across the entire brain in order to better understand how memories are stored in neural networks and how multiple memories may coexist. Intact tissue clearing and imaging is a new and rapidly growing area of focus that could accomplish this task. Here, we utilized the leading protocols for whole-brain clearing and applied them to the ArcCreERT2 mice, a murine line that allows for the indelible labeling of memory traces. We found that CLARITY and PACT greatly distorted the tissue, and iDISCO quenched enhanced yellow fluorescent protein (EYFP) fluorescence and hindered immunolabeling. Alternative clearing solutions, such as tert-Butanol, circumvented these harmful effects, but still did not permit whole-brain immunolabeling. CUBIC and CUBIC with Reagent-1A produced improved antibody penetration and preserved EYFP fluorescence, but also did not allow for whole-brain memory trace visualization. Modification of CUBIC with Reagent-1A resulted in EYFP fluorescence preservation and immunolabeling of the immediate early gene (IEG) Arc in deep brain areas; however, optimized memory trace labeling still required tissue slicing into mm-thick tissue sections. In summary, our data show that CUBIC with Reagent-1A* is the ideal method for reproducible clearing and immunolabeling for the visualization of memory traces in mm-thick tissue sections from ArcCreERT2 mice.

PGE2-EP3 signaling exacerbates hippocampus-dependent cognitive impairment after laparotomy by reducing expression levels of hippocampal synaptic plasticity-related proteins in aged mice.

AIM: Multifactors contribute to the development of postoperative cognitive dysfunction (POCD), of which the most important mechanism is neuroinflammation. Prostaglandin E2 (PGE2) is a key neuroinflammatory molecule and could modulate hippocampal synaptic transmission and plasticity. This study was designed to investigate whether PGE2 and its receptors signaling pathway were involved in the pathophysiology of POCD. METHODS: Sixteen-month old male C57BL/6J mice were exposed to laparotomy. Cognitive function was evaluated by fear conditioning test. The levels of PGE2 and its 4 distinct receptors (EP1-4) were assessed by biochemical analysis. Pharmacological or genetic methods were further applied to investigate the role of the specific PGE2 receptors. RESULTS: Here, we found that the transcription and translation level of the EP3 receptor in hippocampus increased remarkably, but not EP1, EP2, or EP4. Immunofluorescence results showed EP3 positive cells in the hippocampal CA1 region were mainly neurons. Furthermore, pharmacological blocking or genetic suppression of EP3 could alleviate surgery-induced hippocampus-dependent memory deficits and rescued the expression of plasticity-related proteins, including cAMP response element-binding protein (CREB), activity-regulated cytoskeletal-associated protein (Arc), and brain-derived neurotrophic factor (BDNF) in hippocampus. CONCLUSION: This study showed that PGE2-EP3 signaling pathway was involved in the progression of POCD and identified EP3 receptor as a promising treatment target.

Different doses of sevoflurane facilitate and impair learning and memory function through activation of the ERK pathway and synthesis of ARC protein in the rat hippocampus.

BACKGROUND: Sevoflurane has been shown to stimulate or depress memory in adult rats; however, the cellular mechanism of this bidirectional effect has not been fully investigated. METHODS: We used an intra-hippocampal microinfusion of U0126 to suppress ERK activation. Male SD rats were randomly assigned to four groups: Sham, 0.11%SEV, 0.3%SEV and 0.3%+U0126. They received bilateral injections of U0126 or saline. Rats were anesthetized, and Inhibitory Avoidance (IA) training was performed immediately after anesthesia. The memory retention latency was observed 24 h later. In another experiment, the hippocampus was removed 45 min after IA training to assess ARC expression, the synapsin 1 protein levels and the phosphorylation level of ERK. RESULTS: Treatment with 0.11%SEV led to rapid phosphorylation of ERK, while 0.3%SEV inhibited phosphorylation; the latter change was reversed by the microinfusion of U0126 in the hippocampus. The memory latency result had similar tendencies. The local infusion of U0126 abolished the 0.3%SEV-induced memory impairment and ERK inhibition. Selective upregulations of ARC and synapsin 1 proteins were observed in the 0.3%SEV group compared with the 0.11%SEV group. CONCLUSIONS: The results indicate that different doses of sevoflurane trigger synaptic plasticity-related cytoskeleton proteins through the ERK signaling pathway. This novel modulation by inhalational agents may help to reduce their side-effects on memory function.

Rehabilitation modality and onset differentially influence whisker sensory hypersensitivity after diffuse traumatic brain injury in the rat.

BACKGROUND: As rehabilitation strategies advance as therapeutic interventions, the modality and onset of rehabilitation after traumatic brain injury (TBI) are critical to optimize treatment. Our laboratory has detected and characterized a late-onset, long-lasting sensory hypersensitivity to whisker stimulation in diffuse brain-injured rats; a deficit that is comparable to visual or auditory sensory hypersensitivity in humans with an acquired brain injury. OBJECTIVE: We hypothesize that the modality and onset of rehabilitation therapies will differentially influence sensory hypersensitivity in response to the Whisker Nuisance Task (WNT) as well as WNT-induced corticosterone (CORT) stress response in diffuse brain-injured rats and shams. METHODS: After midline fluid percussion brain injury (FPI) or sham surgery, rats were assigned to one of four rehabilitative interventions: (1) whisker sensory deprivation during week one or (2) week two or (3) whisker stimulation during week one or (4) week two. At 28 days following FPI and sham procedures, sensory hypersensitivity was assessed using the WNT. Plasma CORT was evaluated immediately following the WNT (aggravated levels) and prior to the pre-determined endpoint 24 hours later (non-aggravated levels). RESULTS: Deprivation therapy during week two elicited significantly greater sensory hypersensitivity to the WNT compared to week one (p < 0.05), and aggravated CORT levels in FPI rats were significantly lower than sham levels. Stimulation therapy during week one resulted in low levels of sensory hypersensitivity to the WNT, similar to deprivation therapy and naïve controls, however, non-aggravated CORT levels in FPI rats were significantly higher than sham. CONCLUSION: These data indicate that modality and onset of sensory rehabilitation can differentially influence FPI and sham rats, having a lasting impact on behavioral and stress responses to the WNT, emphasizing the necessity for continued evaluation of modality and onset of rehabilitation after TBI.

Higher Arc Nucleus-to-Cytoplasm Ratio during Sleep in the Superficial Layers of the Mouse Cortex.

The activity-regulated cytoskeleton associated protein Arc is strongly and quickly upregulated by neuronal activity, synaptic potentiation and learning. Arc entry in the synapse is followed by the endocytosis of glutamatergic AMPA receptors (AMPARs), and its nuclear accumulation has been shown in vitro to result in a small decline in the transcription of the GluA1 subunit of AMPARs. Since these effects result in a decline in synaptic strength, we asked whether a change in Arc dynamics may temporally correlate with sleep-dependent GluA1 down-regulation. We measured the ratio of nuclear to cytoplasmic Arc expression (Arc Nuc/Cyto) in the cerebral cortex of EGFP-Arc transgenic mice that were awake most of the night and then perfused immediately before lights on (W mice), or were awake most of the night and then allowed to sleep (S mice) or sleep deprived (SD mice) for the first 2 h of the light phase. In primary motor cortex (M1), neurons with high levels of nuclear Arc (High Arc cells) were present in all mice, but in these cells Arc Nuc/Cyto was higher in S mice than in W mice and, importantly, ~15% higher in S mice than in SD mice collected at the same time of day, ruling out circadian effects. Greater Arc Nuc/Cyto with sleep was observed in the superficial layers of M1, but not in the deep layers. In High Arc cells, Arc Nuc/Cyto was also ~15%-30% higher in S mice than in W and SD mice in the superficial layers of primary somatosensory cortex (S1) and cingulate cortex area 1 (Cg1). In High Arc Cells of Cg1, Arc Nuc/Cyto and cytoplasmic levels of GluA1 immunoreactivities in the soma were also negatively correlated, independent of behavioral state. Thus, Arc moves to the nucleus during both sleep and wake, but its nuclear to cytoplasmic ratio increases with sleep in the superficial layers of several cortical areas. It remains to be determined whether the relative increase in nuclear Arc contributes significantly to the overall decline in the strength of excitatory synapses that occurs during sleep. Similarly, it remains to be determined whether the entry of Arc into specific synapses is gated by sleep.

Dissociation between complete hippocampal context memory formation and context fear acquisition.

Rodents require a minimal time period to explore a context prior to footshock to display plateau-level context fear at test. To investigate whether this rapid fear plateau reflects complete memory formation within that short time-frame, we used the immediate-early gene product Arc as an indicator of hippocampal context memory formation-related activity. We found that hippocampal Arc expression continued to increase well past the minimal time required for plateau-level fear. This raises the possibility that context fear conditioning occurs more rapidly than complete memory formation. Thus, animals may be able to condition robustly to both complete and incomplete contextual representations.

Dopamine is Required for Activity-Dependent Amplification of Arc mRNA in Developing Postnatal Frontal Cortex.

The activity-regulated gene Arc/Arg3.1 encodes a postsynaptic protein crucially involved in glutamatergic synaptic plasticity. Genetic mutations in Arc pathway and altered Arc expression in human frontal cortex have been associated with schizophrenia. Although Arc expression has been reported to vary with age, what mechanisms regulate Arc mRNA levels in frontal cortex during postnatal development remains unclear. Using quantitative mRNA analysis of mouse frontal cortical tissues, we mapped the developmental profiles of Arc expression and found that its mRNA levels are sharply amplified near the end of the second postnatal week, when mouse pups open their eyes for the first time after birth. Surprisingly, electrical stimulation of the frontal cortex before eye-opening is not sufficient to drive the amplification of Arc mRNA. Instead, this amplification needs both electrical stimulation and dopamine D1-type receptor (D1R) activation. Furthermore, visual stimuli-driven amplification of Arc mRNA is also dependent on D1R activation and dopamine neurons located in the ventral midbrain. These results indicate that dopamine is required to drive activity-dependent amplification of Arc mRNA in the developing postnatal frontal cortex and suggest that joint electrical and dopaminergic activation is essential to establish the normal expression pattern of a schizophrenia-associated gene during frontal cortical development.

A novel escapable social interaction test reveals that social behavior and mPFC activation during an escapable social encounter are altered by post-weaning social isolation and are dependent on the aggressiveness of the stimulus rat.

Post-weaning social isolation (PSI) has been shown to increase aggressive behavior and alter medial prefrontal cortex (mPFC) function in social species such as rats. Here we developed a novel escapable social interaction test (ESIT) allowing for the quantification of escape and social behaviors in addition to mPFC activation in response to an aggressive or nonaggressive stimulus rat. Male rats were exposed to 3 weeks of PSI (ISO) or group (GRP) housing, and exposed to 3 trials, with either no trial, all trials, or the last trial only with a stimulus rat. Analysis of social behaviors indicated that ISO rats spent less time in the escape chamber and more time engaged in social interaction, aggressive grooming, and boxing than did GRP rats. Interestingly, during the third trial all rats engaged in more of the quantified social behaviors and spent less time escaping in response to aggressive but not nonaggressive stimulus rats. Rats exposed to nonaggressive stimulus rats on the third trial had greater c-fos and ARC immunoreactivity in the mPFC than those exposed to an aggressive stimulus rat. Conversely, a social encounter produced an increase in large PSD-95 punctae in the mPFC independently of trial number, but only in ISO rats exposed to an aggressive stimulus rat. The results presented here demonstrate that PSI increases interaction time and aggressive behaviors during escapable social interaction, and that the aggressiveness of the stimulus rat in a social encounter is an important component of behavioral and neural outcomes for both isolation and group-reared rats.

Sweet orosensation induces Arc expression in dorsal hippocampal CA1 neurons in an experience-dependent manner.

There is limited knowledge regarding how the brain controls the timing of meals. Similarly, there is a large gap in our understanding of how top-down cognitive processes, such as memory influence energy intake. We hypothesize that dorsal hippocampal (dHC) neurons, which are critical for episodic memory, form a memory of a meal and inhibit meal onset during the postprandial period. In support, we showed previously that reversible inactivation of these neurons during the period following a sucrose meal accelerates the onset of the next meal. If dHC neurons form a memory of a meal, then consumption should induce synaptic plasticity in dHC neurons. To test this, we determined (1) whether a sucrose meal increases the expression of the synaptic plasticity marker activity-regulated cytoskeleton-associated protein (Arc) in dHC CA1 neurons, (2) whether previous experience with sucrose influences sucrose-induced Arc expression, and (3) whether the orosensory stimulation produced by the noncaloric sweetener saccharin is sufficient to induce Arc expression. Male Sprague-Dawley rats were trained to consume a sweetened solution at a scheduled time daily. On the experimental day, they were given a solution for 7 min, euthanized, and then fluorescence in situ hybridization procedures were used to measure meal-induced Arc mRNA. Compared to caged control rats, Arc expression was significantly higher in rats that consumed sucrose or saccharin. Interestingly, rats given additional experience with sucrose had less Arc expression than rats with less sucrose experience, even though both groups consumed similar amounts on the experimental day. Thus, this study is the first to suggest that orosensory stimulation produced by consuming a sweetened solution and possibly the hedonic value of that sweet stimulation induces synaptic plasticity in dHC CA1 neurons in an experience-dependent manner. Collectively, these findings are consistent with our hypothesis that dHC neurons form a memory of a meal.

From Memory Impairment to Posttraumatic Stress Disorder-Like Phenotypes: The Critical Role of an Unpredictable Second Traumatic Experience.

Arousal and stress critically regulate memory formation and retention. Increasing levels of stress produce an inverted U-shaped effect on cognitive performance, including the retention of explicit memories, and experiencing a severe stress during a traumatic event may lead to posttraumatic stress disorder (PTSD). The molecular mechanisms underlying the impairing effect of a severe stress on memory and the key contribution of traumatic experiences toward the development of PTSD are still unknown. Here, using increasing footshock intensities in an inhibitory avoidance paradigm, we reproduced the inverted U-shaped curve of memory performance in rats. We then show that the inverted U profile of memory performance correlates with an inverted U profile of corticosterone level in the circulation and of brain-derived neurotrophic factor, phosphorylated tropomyosin-receptor kinase B, and methyl CpG binding protein in the dorsal hippocampus. Furthermore, training with the highest footshock intensity (traumatic experience) led to a significant elevation of hippocampal glucocorticoid receptors. Exposure to an unpredictable, but not to a predictable, highly stressful reminder shock after a first traumatic experience resulted in PTSD-like phenotypes, including increased memory of the trauma, high anxiety, threat generalization, and resistance to extinction. Systemic corticosterone injection immediately after the traumatic experience, but not 3 d later, was sufficient to produce PTSD-like phenotypes. We suggest that, although after a first traumatic experience a suppression of the corticosterone-dependent response protects against the development of an anxiety disorder, experiencing more than one trauma (multiple hits) is a critical contributor to the etiology of PTSD.

Chronic morphine treatment enhances sciatic nerve stimulation-induced immediate early gene expression in the rat dorsal horn.

Synaptic plasticity is a property of neurons that can be induced by conditioning electrical stimulation (CS) of afferent fibers in the spinal cord. This is a widely studied property of spinal cord and hippocampal neurons. CS has been shown to trigger enhanced expression of immediate early gene proteins (IEGPs), with peak increases observed 2 hour post stimulation. Chronic morphine treatment has been shown to promoteinduce opioid-induced hyperalgesia, and also to increase CS-induced central sensitization in the dorsal horn. As IEGP expression may contribute to development of chronic pain states, we aimed to determine whether chronic morphine treatment affects the expression of IEGPs following sciatic nerve CS. Changes in expression of the IEGPs Arc, c-Fos or Zif268 were determined in cells of the lumbar dorsal horn of the spinal cord. Chronic Morphine pretreatment over 7 days led to a significant increase in the number of IEGP positive cells observed at both 2 h and 6 h after CS. The same pattern of immunoreactivity was obtained for all IEGPs, with peak increases occurring at 2 h post CS. In contrast, morphine treatment alone in sham operated animals had no effect on IEGP expression. We conclude that chronic morphine treatment enhances stimulus-induced expression of IEGPs in the lumbar dorsal horn. These data support the notion that morphine alters gene expression responses linked to nociceptive stimulation and plasticity.

Alterations in primary motor cortex neurotransmission and gene expression in hemi-parkinsonian rats with drug-induced dyskinesia.

Treatment of Parkinson's disease (PD) with dopamine replacement relieves symptoms of poverty of movement, but often causes drug-induced dyskinesias. Accumulating clinical and pre-clinical evidence suggests that the primary motor cortex (M1) is involved in the pathophysiology of PD and that modulating cortical activity may be a therapeutic target in PD and dyskinesia. However, surprisingly little is known about how M1 neurotransmitter tone or gene expression is altered in PD, dyskinesia or associated animal models. The present study utilized the rat unilateral 6-hydroxydopamine (6-OHDA) model of PD/dyskinesia to characterize structural and functional changes taking place in M1 monoamine innervation and gene expression. 6-OHDA caused dopamine pathology in M1, although the lesion was less severe than in the striatum. Rats with 6-OHDA lesions showed a PD motor impairment and developed dyskinesia when given L-DOPA or the D1 receptor agonist, SKF81297. M1 expression of two immediate-early genes (c-Fos and ARC) was strongly enhanced by either L-DOPA or SKF81297. At the same time, expression of genes specifically involved in glutamate and GABA signaling were either modestly affected or unchanged by lesion and/or treatment. We conclude that M1 neurotransmission and signal transduction in the rat 6-OHDA model of PD/dyskinesia mirror features of human PD, supporting the utility of the model to study M1 dysfunction in PD and the elucidation of novel pathophysiological mechanisms and therapeutic targets.

Hunger States Control the Directions of Synaptic Plasticity via Switching Cell Type-Specific Subunits of NMDA Receptors.

It remains largely unknown whether and how hunger states control activity-dependent synaptic plasticity, such as long-term potentiation (LTP) and long-term depression (LTD). We here report that both LTP and LTD of excitatory synaptic strength within the appetite control circuits residing in hypothalamic arcuate nucleus (ARC) behave in a manner of hunger states dependence and cell type specificity. For instance, we find that tetanic stimulation induces LTP at orexigenic agouti-related protein (AgRP) neurons in ad libitum fed mice, whereas it induces LTD in food-deprived mice. In an opposite direction, the same induction protocol induces LTD at anorexigenic pro-opiomelanocortin (POMC) neurons in fed mice but weak LTP in deprived mice. Mechanistically, we also find that food deprivation increases the expressions of NR2C/NR2D/NR3-containing NMDA receptors (NMDARs) at AgRP neurons that contribute to the inductions of LTD, whereas it decreases their expressions at POMC neurons. Collectively, our data reveal that hunger states control the directions of activity-dependent synaptic plasticity by switching NMDA receptor subpopulations in a cell type-specific manner, providing insights into NMDAR-mediated interactions between energy states and associative memory. Significance statement: Based on the experiments performed in this study, we demonstrate that activity-dependent synaptic plasticity is also under the control of energy states by regulating NMDAR subpopulations in a cell type-specific manner. We thus propose a reversible memory configuration constructed from energy states-dependent cell type-specific bidirectional conversions of LTP and LTD. Together with the distinct functional roles played by NMDAR signaling in the control of food intake and energy states, these findings reveal a new reciprocal interaction between energy states and associative memory, one that might serve as a target for therapeutic treatments of the energy-related memory disorders or vice versa.

Calcium dysregulation via L-type voltage-dependent calcium channels and ryanodine receptors underlies memory deficits and synaptic dysfunction during chronic neuroinflammation.

BACKGROUND: Chronic neuroinflammation and calcium (Ca(+2)) dysregulation are both components of Alzheimer's disease. Prolonged neuroinflammation produces elevation of pro-inflammatory cytokines and reactive oxygen species which can alter neuronal Ca(+2) homeostasis via L-type voltage-dependent Ca(+2) channels (L-VDCCs) and ryanodine receptors (RyRs). Chronic neuroinflammation also leads to deficits in spatial memory, which may be related to Ca(+2) dysregulation. METHODS: The studies herein use an in vivo model of chronic neuroinflammation: rats were infused intraventricularly with a continuous small dose of lipopolysaccharide (LPS) or artificial cerebrospinal fluid (aCSF) for 28 days. The rats were treated with the L-VDCC antagonist nimodipine or the RyR antagonist dantrolene. RESULTS: LPS-infused rats had significant memory deficits in the Morris water maze, and this deficit was ameliorated by treatment with nimodipine. Synaptosomes from LPS-infused rats had increased Ca(+2) uptake, which was reduced by a blockade of L-VDCCs either in vivo or ex vivo. CONCLUSIONS: Taken together, these data indicate that Ca(+2) dysregulation during chronic neuroinflammation is partially dependent on increases in L-VDCC function. However, blockade of the RyRs also slightly improved spatial memory of the LPS-infused rats, demonstrating that other Ca(+2) channels are dysregulated during chronic neuroinflammation. Ca(+2)-dependent immediate early gene expression was reduced in LPS-infused rats treated with dantrolene or nimodipine, indicating normalized synaptic function that may underlie improvements in spatial memory. Pro-inflammatory markers are also reduced in LPS-infused rats treated with either drug. Overall, these data suggest that Ca(+2) dysregulation via L-VDCCs and RyRs play a crucial role in memory deficits resulting from chronic neuroinflammation.

Progressive recruitment of cortical and striatal regions by inducible postsynaptic density transcripts after increasing doses of antipsychotics with different receptor profiles: insights for psychosis treatment.

Antipsychotics may modulate the transcription of multiple gene programs, including those belonging to postsynaptic density (PSD) network, within cortical and subcortical brain regions. Understanding which brain region is activated progressively by increasing doses of antipsychotics and how their different receptor profiles may impact such an activation could be relevant to better correlate the mechanism of action of antipsychotics both with their efficacy and side effects. We analyzed the differential topography of PSD transcripts by incremental doses of two antipsychotics: haloperidol, the prototypical first generation antipsychotic with prevalent dopamine D2 receptors antagonism, and asenapine, a second generation antipsychotic characterized by multiple receptors occupancy. We investigated the expression of PSD genes involved in synaptic plasticity and previously demonstrated to be modulated by antipsychotics: Homer1a, and its related interacting constitutive genes Homer1b/c and PSD95, as well as Arc, C-fos and Zif-268, also known to be induced by antipsychotics administration. We found that increasing acute doses of haloperidol induced immediate-early genes (IEGs) expression in different striatal areas, which were progressively recruited by incremental doses with a dorsal-to-ventral gradient of expression. Conversely, increasing acute asenapine doses progressively de-recruited IEGs expression in cortical areas and increased striatal genes signal intensity. These effects were mirrored by a progressive reduction in locomotor animal activity by haloperidol, and an opposite increase by asenapine. Thus, we demonstrated for the first time that antipsychotics may progressively recruit PSD-related IEGs expression in cortical and subcortical areas when administered at incremental doses and these effects may reflect a fine-tuned dose-dependent modulation of the PSD.