Molecular mechanisms mediating gastrin-releasing peptide receptor modulation of memory consolidation in the hippocampus

IL-6 Enhances the Activation of PI3K-AKT/mTOR-GSK-3β by Upregulating GRPR in Hippocampal Neurons of Autistic Mice

Autism spectrum disorder (ASD) is a neurological disorder associated with brain inflammation. The underlying mechanisms could be attributed to the activation of PI3K signaling in the inflamed brain of ASD. Multiple studies highlight the role of GRPR in regulating ASD like abnormal behavior and enhancing the PI3K signaling. However, the molecular mechanism by which GRPR regulates PI3K signaling in neurons of individuals with ASD is still unclear. In this study, we utilized a maternal immune activation model to investigate the effects of GRPR on PI3K signaling in the inflamed brain of ASD mice. We used HT22 cells with and without GRPR to examine the impact of GRP-GRPR on the PI3K-AKT pathway with IL-6 treatment. We analyzed a dataset of hippocampus samples from ASD mice to identify hub genes. Our results demonstrated increased expression of IL-6, GRPR, and PI3K-AKT signaling in the hippocampus of ASD mice. Additionally, we observed increased GRPR expression and PI3K-AKT/mTOR activation in HT22 cells after IL-6 treatment, but decreased expression in HT22 cells with GRPR knockdown. NetworkAnalyst identified GSK-3β as the most crucial gene in the PI3K-AKT/mTOR pathway in the hippocampus of ASD. Furthermore, we found that IL-6 upregulated the expression of GSK-3β in HT22 cells by upregulating GRP-GRPR. Our findings suggest that IL-6 can enhance the activation of PI3K-AKT/mTOR-GSK-3β in hippocampal neurons of ASD mice by upregulating GRPR.

Advances of radiolabeled GRPR ligands for PET/CT imaging of cancers

GRPR is a type of seven-transmembrane G-protein coupled receptor that belongs to the bombesin protein receptor family. It is highly expressed in various cancers, including prostate cancer, breast cancer, lung cancer, gastrointestinal cancer, and so on. As a result, molecular imaging studies have been conducted using radiolabeled GRPR ligands for tumor diagnosis, as well as monitoring of recurrence and metastasis. In this paper, we provided a comprehensive overview of relevant literature from the past two decades, with a specific focus on the advancements made in radiolabeled GRPR ligands for imaging prostate cancer and breast cancer.

Bombesins: A New Frontier in Hybrid Compound Development

Recently, bombesin (BN) and its analogs have attracted much attention as excellent anticancer agents because they interact with specific receptors widely distributed on the surface of various cancer cells. However, their biological properties proceed far beyond this, given a broad spectrum of activity. Bombesin receptor ligands are effective drugs for the treatment of rheumatoid arthritis or gastrointestinal diseases. However, most diseases are complex, and the use of polytherapy may lead to pharmacokinetic and pharmacodynamic drug-drug interactions, resulting in side effects. Therefore, there is a need to develop effective compounds that also contain BN or its analogs, which are combined with other structural entities, thus generating a so-called hybrid drug. Hybrid drugs that contain bombesin pharmacophore(s) may be proposed as a solution to the problem of polytherapy or the lack of an effective cure. Such structures have now demonstrated the desired efficacy, though information on these aforementioned compounds is relatively scarce. Therefore, our paper aims to encourage researchers to focus on bombesins. Herein, we indicate that the hybrid approach should also be firmly applied to bombesins and the BN receptor family. This paper's structure is divided into two main sections demonstrating bombesins and their properties, as well as recent data on bombesin-based hybrid compounds and their potential usefulness in medicine. Overall, it refers to the discovery and synthesis of modified bombesin-based hybrid compounds.

Role of the GRP/GRPR System in Regulating Brain Functions

Re-examining the relationship between neuropeptide systems and neural circuits will help us to understand more intensively the critical role of neuropeptides in brain function as the neural circuits responsible for specific brain functions are gradually revealed. Gastrin-releasing peptide receptors (GRPRs) are Gαq-coupling neuropeptide receptors and widely distributed in the brain, including hippocampus, amygdala, hypothalamus, nucleus tractus solitarius (NTS), suprachiasmatic nucleus (SCN), paraventricular nucleus of the hypothalamus (PVN), preoptic area of the hypothalamus (POA), preBötzinger complex (preBötC), etc., implying the GRP/GRPR system is involved in modulating multiple brain functions. In this review, we focus on the functionality of GRPR neurons and the regulatory role of the GRP/GRPR system in memory and cognition, fear, depression and anxiety, circadian rhythms, contagious itch, gastric acid secretion, food intake, body temperature, and sighing behavior. It can be found that GRPR is usually centered on a certain brain nucleus or anatomical structure and modulates richer or more specific behaviors by connecting with additional different nuclei. In order to explain the regulatory mechanism of the GRP/GRPR system, more precise intervention methods are needed.

Serum Metabolites Differentiate Amnestic Mild Cognitive Impairment From Healthy Controls and Predict Early Alzheimer's Disease via Untargeted Lipidomics Analysis

Background and Aim: Alzheimer's disease (AD) is the most common type of dementia and presents with metabolic perturbations early in the disease process. In order to explore biomarkers useful in predicting early AD, we compared serum metabolites among patients suffering different stages of AD.

Methods: We recruited 107 participants including 23 healthy controls (HC), 21 amnestic mild cognitive impairment (aMCI), 24 non-amnestic mild cognitive impairment (naMCI) and 39 AD patients. Via liquid chromatography-mass spectrometry based serum untargeted lipidomics analysis, we compared differences in serum lipid metabolites among these patient groups and further elucidated biomarkers that differentiate aMCI from HC.

Results: There were significant differences of serum lipid metabolites among the groups, and 20 metabolites were obtained under negative ion mode from HC and aMCI comparison. Notably, 16:3 cholesteryl ester, ganglioside GM3 (d18:1/9z-18:1) and neuromedin B were associated with cognition and increased the predictive effect of aMCI to 0.98 as revealed by random forest classifier. The prediction model composed of MoCA score, 16:3 cholesteryl ester and ganglioside GM3 (d18:1/9z-18:1) had good predictive performance for aMCI. Glycerophospholipid metabolism was a pathway common among HC/aMCI and aMCI/AD groups.

Conclusion: This study provides preliminary evidence highlighting that 16:3 cholesteryl ester were useful for AD disease monitoring while ganglioside GM3 (d18:1/9z-18:1) and neuromedin B discriminated aMCI from HC, which can probably be applied in clinic for early predicting of AD.

Can dipeptidyl peptidase-4 inhibitors treat cognitive disorders?

The linkage of neurodegenerative diseases with insulin resistance (IR) and type 2 diabetes mellitus (T2DM), including oxidative stress, mitochondrial dysfunction, excessive inflammatory responses and abnormal protein processing, and the correlation between cerebrovascular diseases and hyperglycemia has opened a new window for novel therapeutics for these cognitive disorders. Various antidiabetic agents have been studied for their potential treatment of cognitive disorders, among which the dipeptidyl peptidase-4 (DPP-4) inhibitors have been investigated more recently. So far, DPP-4 inhibitors have demonstrated neuroprotection and cognitive improvements in animal models, and cognitive benefits in diabetic patients with or without cognitive impairments. This review aims to summarize the potential mechanisms, advantages and limitations, and currently available evidence for developing DPP-4 inhibitors as a treatment of cognitive disorders.

Lithium alters expression of RNAs in a type-specific manner in differentiated human neuroblastoma neuronal cultures, including specific genes involved in Alzheimer's disease

Lithium (Li) is a medication long-used to treat bipolar disorder. It is currently under investigation for multiple nervous system disorders, including Alzheimer's disease (AD). While perturbation of RNA levels by Li has been previously reported, its effects on the whole transcriptome has been given little attention. We, therefore, sought to determine comprehensive effects of Li treatment on RNA levels. We cultured and differentiated human neuroblastoma (SK-N-SH) cells to neuronal cells with all-trans retinoic acid (ATRA). We exposed cultures for one week to lithium chloride or distilled water, extracted total RNA, depleted ribosomal RNA and performed whole-transcriptome RT-sequencing. We analyzed results by RNA length and type. We further analyzed expression and protein interaction networks between selected Li-altered protein-coding RNAs and common AD-associated gene products. Lithium changed expression of RNAs in both non-specific (inverse to sequence length) and specific (according to RNA type) fashions. The non-coding small nucleolar RNAs (snoRNAs) were subject to the greatest length-adjusted Li influence. When RNA length effects were taken into account, microRNAs as a group were significantly less likely to have had levels altered by Li treatment. Notably, several Li-influenced protein-coding RNAs were co-expressed or produced proteins that interacted with several common AD-associated genes and proteins. Lithium's modification of RNA levels depends on both RNA length and type. Li activity on snoRNA levels may pertain to bipolar disorders while Li modification of protein coding RNAs may be relevant to AD.

Gastrin-releasing peptide inhibits CA1 neurons via increasing inhibitory synaptic transmissions in hippocampal slices of rats

Gastrin-releasing peptide plays an important role in regulating the advanced functions of the brain including emotional behavior, learning and memory. What's more, gastrin-releasing peptide levels are also associated with the central nervous system diseases. Our previous study proposed that intraperitoneal injection of gastrin-releasing peptide can improve spatial memory in chronic ischemic model rats. It is well known that the hippocampus is an important brain area related to spatial learning and memory, but the mechanisms of gastrin-releasing peptide on hippocampal neurons are still unclear. In this study, we examined the effects of gastrin-releasing peptide on excitability of hippocampal CA1 neurons and further explored the mechanisms of its effects on synaptic transmission. The results showed that gastrin-releasing peptide inhibited the excitability of CA1 neurons and increased the amplitude and frequency of inhibitory postsynaptic currents significantly. In summary, we demonstrate that gastrin-releasing peptide can inhibit the excitability of hippocampal CA1 area neurons in brain slices and clarify the synaptic transmission mechanism involved in this process, which provide a theoretical basis for gastrin-releasing peptide to improve animal cognitive function, and new ideas for the treatment of related central nervous system diseases.

Maternal high-fat diet results in cognitive impairment and hippocampal gene expression changes in rat offspring

Consumption of a high-fat diet has long been known to increase risk for obesity, diabetes, and the metabolic syndrome. Further evidence strongly suggests that these same metabolic disorders are associated with an increased risk of cognitive impairment later in life. Now faced with an expanding global burden of obesity and increasing prevalence of dementia due to an aging population, understanding the effects of high-fat diet consumption on cognition is of increasingly critical importance. Further, the developmental origins of many adult onset neuropsychiatric disorders have become increasingly clear, indicating a need to investigate effects of various risk factors, including diet, across the lifespan. Here, we use a rat model to assess the effects of maternal diet during pregnancy and lactation on cognition and hippocampal gene expression of offspring. Behaviorally, adult male offspring of high-fat fed dams had impaired object recognition memory and impaired spatial memory compared to offspring of chow-fed dams. In hippocampus, we found decreased expression of Insr, Lepr, and Slc2a1 (GLUT1) among offspring of high-fat fed dams at postnatal day 21. The decreased expression of Insr and Lepr persisted at postnatal day 150. Together, these data provide additional evidence to suggest that maternal exposure to high-fat diet during pregnancy and lactation can have lasting effects on the brain, behavior, and cognition on adult offspring.

Machine learning in schizophrenia genomics, a case-control study using 5,090 exomes

Our hypothesis is that machine learning (ML) analysis of whole exome sequencing (WES) data can be used to identify individuals at high risk for schizophrenia (SCZ). This study applies ML to WES data from 2,545 individuals with SCZ and 2,545 unaffected individuals, accessed via the database of genotypes and phenotypes (dbGaP). Single nucleotide variants and small insertions and deletions were annotated by ANNOVAR using the reference genome hg19/GRCh37. Rare (predicted functional) variants with a minor allele frequency ≤1% and genotype quality ≥90 including missense, frameshift, stop gain, stop loss, intronic, and exonic splicing variants were selected. A file containing all cases and controls, the names of genes with variants meeting our criteria, and the number of variants per gene for each individual, was used for ML analysis. The supervised machine-learning algorithm used the patterns of variants observed in the different genes to determine which subset of genes can best predict that an individual is affected. Seventy percent of the data was used to train the algorithm and the remaining 30% of data (n = 1,526) was used to evaluate its efficiency. The supervised ML algorithm, gradient boosted trees with regularization (eXtreme Gradient Boosting implementation) was the best performing algorithm yielding promising results (accuracy: 85.7%, specificity: 86.6%, sensitivity: 84.9%, area under the receiver-operator characteristic curve: 0.95). The top 50 features (genes) of the algorithm were analyzed using bioinformatics resources for new insights about the pathophysiology of SCZ. This manuscript presents a novel predictor which could potentially enable studies exploring disease-modifying intervention in the early stages of the disease.

Keeping Neurons Young and Foxy: FoxOs Promote Neuronal Plasticity

Any adult who has tried to take up the piano or learn a new language is faced with the sobering realization that acquiring such skills is more challenging as an adult than as a child. Neuronal plasticity, or the malleability of brain circuits, declines with age. Young neurons tend to be more adaptable and can alter the size and strength of their connections more readily than can old neurons. Myriad circuit- and synapse-level mechanisms that shape plasticity have been identified. Yet, molecular mechanisms setting the overall competence of young neurons for distinct forms of plasticity remain largely obscure. Recent studies indicate evolutionarily conserved roles for FoxO proteins in establishing the capacity for cell-fate, morphological, and synaptic plasticity in neurons.

Bombesin-induced enhancement of memory consolidation in male and female rat pups: Role of glutamatergic and dopaminergic systems

Previous studies have shown that the neuropeptide bombesin (BBS) enhances consolidation of specifically for inhibitory avoidance memory in adult rats. However, its effect on memory consolidation during premature period is not clear as well. Thus, this study evaluated the effect of BBS and its interaction with glutamatergic and dopaminergic systems on memory consolidation in rat pups. Male and female rat pups (30 days old) were trained in an inhibitory avoidance (IA) task (0.5 mA, 3 s footshock). Memory retention was tested 24 h later during which the latency to re-enter to the shock compartment was recorded. First, the effects of different doses (0.001, 0.0025, 0.005, 0.01 and 0.02 mg/kg) of BBS injected immediately following training were tested. Then, the effect of the most effective dose of BBS obtained in the previous experiment was examined in the presence of the glutamate NMDA receptor antagonist MK-801 (0.05 mg/kg), the dopamine D1 receptor antagonist SCH-23390 (0.05 mg/kg) and the dopamine D2 receptor antagonist sulpiride (20 mg/kg). Findings indicate that BBS significantly enhances memory consolidation at all tested doses in male pups and at a dose of 0.01 mg/kg in female pups. MK-801, SCH-23390 and sulpiride administration before BBS injection in individual groups significantly blocked BBS-induced memory enhancement. Our findings indicate that similar to adult rats, BBS enhances memory consolidation in developing rat. This enhancing effect is mediated, at least in part, via an interaction with glutamatergic and dopaminergic systems.

Gastrin-releasing peptide attenuates fear memory reconsolidation

BACKGROUND

Gastrin Releasing Peptide (GRP) may play a role in fear learning. The GRP Receptor is expressed in the basolateral amygdala and hippocampus, and central administration of GRP mediates fear learning. The effects of GRP on reconsolidation, however, have been minimally explored. Reconsolidation, the process by which formed memories are rendered labile following recall, provides a window of opportunity for pharmacological intervention. Although evidence suggests the window of opportunity to alter reactivated consolidation memory can be as long as 6 h, shorter intervals have not been extensively investigated.

METHOD

Male Sprague-Dawley rats received six 1.0 mA continuous footshocks. 24 h later, were re-exposed to the context (shock chamber). Immediately following memory retrieval rats received i.p. injection of GRP (10 nmol/kg), Flumazenil (1 mg/kg), GRP + Flumazenil (10 nmol/kg GRP with 1 mg/kg Flumazenil), or Vehicle. Other groups received GRP or Vehicle at 0, 10, 30, or 60 min post-reactivation. 24 h and 5 days later rats were assessed for fear expression upon re-exposure to the fearful stimulus.

RESULTS

GRP significantly attenuated the reconsolidation of learned fear when administered immediately (but not 10 min or longer) following recall. Some of the variability in the impact of treatments aimed at disrupting fear memories may be governed, in part, by the time-frame of the reconsolidation window. Our results indicate that the effect of immediate administration persisted for at least 5 days. Co-administration of benzodiazepine-receptor antagonist Flumazenil blocked this effect, suggesting the effect is mediated via a GABAergic mechanism.

Bombesin attenuated ischemia-induced spatial cognitive and synaptic plasticity impairment associated with oxidative damage

The dysfunction of spatial cognition is a character to various neurological disorders and therapeutic strategy. However, it is limited to known risk factors clinically so far. Gastrin releasing peptide (GRP) signaling is a neuropeptide system mediating emotional memory events. However, the effects of GRP agonist on spatial cognition and hippocampal synaptic plasticity are rarely investigated, especially in pathologic condition. This study was designed to investigate the long-term effects of GRPR agonist, bombesin, against cognitive impairment induced by chronic cerebral ischemia in rats and its possible mechanisms. Our results revealed that bombesin administration (30 μg/kg/day, for 14 continuous days) significantly protected the cognitive and synaptic plasticity impairments as assessed by the Morris water maze and long-term potentiation tests. The mechanism studies demonstrated that bombesin significantly alleviated the decreased activity of total superoxide dismutase (T-SOD), catalase (CAT) and altered the increased the content of malondialdehyde (MDA). Besides, the decreased expression of synapse plasticity-related proteins, calcium- calmodulin- dependent protein kinase II (CaMKII) and synaptophysin (SYP) in the hippocampus were increased with drug treatment. In conclusion, bombesin could protect the oxidative stress and expression of proteins, which were important for synaptic plasticity and cognitive function impairment induced by chronic cerebral ischemia. Our study is presented to provide novel insights into the effects of bombesin on spatial learning and memory, which should be further explored as a potential drug in disorders involving deficits in cognitive function.

Docosahexaenoic Acid Helps to Lessen Extinction Memory in Rats

Abstract: Memory extinction is referred to as a learning process in which a conditioned response (CR) progressively reduces over time as an animal learns to uncouple a response from a stimulus. Extinction occurs when the rat is placed into a context without shock after training. Docosahexaenoic acid (DHA, C22:6, n-3) is implicated in memory formation in mammalian brains. In a two-way active shuttle-avoidance apparatus, we examined whether DHA affects the extinction memory and the expression of brain cognition-related proteins, including gastrin-releasing peptide receptor (GRPR), brain-derived neurotrophic factor receptor (BDNFR) tyrosine kinase receptor B (TrKB), and N-methyl-d-aspartate receptor (NMDAR) subunits NR2A and NR2B. Also, the protein levels of GRP, BDNF, postsynaptic density protein-95 (PSD-95), and vesicular acetylcholine transporter (VAChT), and the antioxidative potentials, in terms of lipid peroxide (LPO) and reactive oxygen species (ROS), were examined in the hippocampus. During the acquisition phase, the rats received a conditioned stimulus (CS-tone) paired with an unconditioned stimulus (UCS foot shock) for three consecutive days (Sessions S1, S2, and S3, each consisting of 30-trials) after 12 weeks of oral administration of DHA. After a three-day interval, the rats were re-subjected to two extinction sessions (S4, S5), each comprising 30 trials of CS alone. During the acquisition training in S1, the shock-related avoidance frequency (acquisition memory) was significantly higher in the DHA-administered rats compared with the control rats. The avoidance frequency, however, decreased with successive acquisition trainings in sessions S2 and S3. When the rats were subjected to the extinction sessions after a break for consolidation, the conditioned response (CR) was also significantly higher in the DHA-administered rats. Interestingly, the freezing responses (frequency and time) also significantly decreased in the DHA-administered rats, thus suggesting that a higher coping capacity was present during fear stress in the DHA-administered rats. DHA treatments increased the mRNA levels of GRPR, BDNF receptor TrKB, and NMDAR subunit NR2B. DHA also increased the protein levels of GRP, BDNF, PSD-95, and VAChT, and the antioxidative potentials in the hippocampus. These results suggest the usefulness of DHA for treating stress disorders.

Recent insights into biological functions of mammalian bombesin-like peptides and their receptors

PURPOSE OF REVIEW

The current review highlights recent advances in physiological and pharmacological researches in biology of mammalian bombesin-like peptides (BLPs).

RECENT FINDINGS

BLPs and their receptors were found to have regulatory roles in many biological processes in central nervous system. Two BLPs, neuromedin B and gastrin-releasing peptide (GRP), and their receptors are required for regulation of basal and induced sighing activity in rodents. This is the first study demonstrating central pathways involved in regulation of sighing activity. GRP receptor (GRPR) expressing neurons are excitatory glutamatergic interneurons located in the dorsal lamina without projections outside the spinal cord and mediate itch signals via vesicular glutamate transporter 2. Those neurons receive itch signals and make synapses with the parabrachial nucleus projecting spinal neurons to transmit itch signals to parabrachial nucleus. GRP expressing interneurons function in a proposed 'leaky gate model' to interpret the mechanism of both pain and itch transmission. In addition to recent advances of biology in nervous system, BLPs and their receptors were found to play potential regulatory roles in innate and adaptive immune responses and tissue development.

SUMMARY

Several important biological roles of BLPs and their receptors in nervous system were identified. Together with researches regarding central roles of BLPs, studies revealing the regulatory roles of BLPs and their receptors in immunology and tissue development provide us with novel insights into understanding of the biology of BLPs and their receptors.

Gastrin-releasing peptide facilitates glutamatergic transmission in the hippocampus and effectively prevents vascular dementia induced cognitive and synaptic plasticity deficits

Neuronal gastrin-releasing peptide (GRP) has been proved to be an important neuromodulator in the brain and involved in a variety of neurological diseases. Whether GRP could attenuate cognition impairment induced by vascular dementia (VD) in rats, and the mechanism of synaptic plasticity and GRP's action on synaptic efficiency are still poorly understood. In this study, we first investigated the effects of GRP on glutamatergic transmission with patch-clamp recording. We found that acute application of GRP enhanced the excitatory synaptic transmission in hippocampal CA1 neurons via GRPR in a presynaptic mechanism. Secondly, we examined whether exogenous GRP or its analogue neuromedin B (NMB) could prevent VD-induced cognitive deficits and the mechanism of synaptic plasticity. By using Morris water maze, long-term potentiation (LTP) recording, western blot assay and immunofluorescent staining, we verified for the first time that GRP or NMB substantially improved the spatial learning and memory abilities in VD rats, restored the impaired synaptic plasticity and was able to elevate the expression of synaptic proteins, synaptophysin (SYP) and CaMKII, which play pivotal roles in synaptic plasticity. These results suggest that the facilitatory effects of GRP on glutamate release may contribute to its long-term action on synaptic efficacy which is essential in cognitive function. Our findings present a new entry point for a better understanding of physiological function of GRP and raise the possibility that GRPR agonists might ameliorate cognitive deficits associated with neurological diseases.

Improvement of autism spectrum disorder symptoms in three children by using gastrin-releasing peptide

OBJECTIVE

To evaluate the safety, tolerability and potential therapeutic effects of gastrin-releasing peptide in three children with autistic spectrum disorder.

METHODS

Case series study with the intravenous administration of gastrin-releasing peptide in the dose of 160pmol/kg for four consecutive days. To evaluate the results, parental impressions the Childhood Autism Rating Scale (CARS) and the Clinical Global Impression (CGI) Scale. Each child underwent a new peptide cycle after two weeks. The children were followed for four weeks after the end of the infusions.

RESULTS

The gastrin-releasing peptide was well tolerated and no child had adverse effects. Two children had improved social interaction, with a slight improvement in joint attention and the interaction initiatives. Two showed reduction of stereotypes and improvement in verbal language. One child lost his compulsion to bathe, an effect that lasted two weeks after each infusion cycle. Average reduction in CARS score was 2.8 points. CGI was "minimally better" in two children and "much better" in one.

CONCLUSIONS

This study suggests that the gastrin-releasing peptide is safe and may be effective in improving key symptoms of autism spectrum disorder, but its results should be interpreted with caution. Controlled clinical trials-randomized, double-blinded, and with more children-are needed to better evaluate the possible therapeutic effects of gastrin-releasing peptide in autism.

Histone deacetylase inhibition prevents the impairing effects of hippocampal gastrin-releasing peptide receptor antagonism on memory consolidation and extinction

Hippocampal gastrin-releasing peptide receptors (GRPR) regulate memory formation and extinction, and disturbances in GRPR signaling may contribute to cognitive impairment associated with neurodevelopmental disorders. Histone acetylation is an important epigenetic mechanism that regulates gene expression involved in memory formation, and histone deacetylase inhibitors (HDACis) rescue memory deficits in several models. The present study determined whether inhibiting histone deacetylation would prevent memory impairments produced by GRPR blockade in the hippocampus. Male Wistar rats were given an intrahippocampal infusion of saline (SAL) or the HDACi sodium butyrate (NaB) shortly before inhibitory avoidance (IA) training, followed by an infusion of either SAL or the selective GRPR antagonist RC-3095 immediately after training. In a second experiment, the infusions were administered before and after a retention test trial that served as extinction training. As expected, RC-3095 significantly impaired consolidation and extinction of IA memory. More importantly, pretraining administration of NaB, at a dose that had no effect when given alone, prevented the effects of RC-3095. In addition, the combination of NaB and RC-3095 increased hippocampal levels of the brain-derived neurotrophic factor (BDNF). These findings indicate that HDAC inhibition can protect against memory impairment caused by GRPR blockade.

A phosphodiesterase 4-controlled switch between memory extinction and strengthening in the hippocampus

Established fear-related memories can undergo phenomena such as extinction or reconsolidation when recalled. Extinction probably involves the creation of a new, competing memory trace that decreases fear expression, whereas reconsolidation can mediate memory maintenance, updating, or strengthening. The factors determining whether retrieval will initiate extinction, reconsolidation, or neither of these two processes include training intensity, duration of the retrieval session, and age of the memory. However, previous studies have not shown that the same behavioral protocol can be used to induce either extinction or reconsolidation and strengthening, depending on the pharmacological intervention used. Here we show that, within an experiment that leads to extinction in control rats, memory can be strengthened if rolipram, a selective inhibitor of phosphodiesterase type 4 (PDE4), is administered into the dorsal hippocampus immediately after retrieval. The memory-enhancing effect of rolipram lasted for at least 1 week, was blocked by the protein synthesis inhibitor anisomycin, and did not occur when drug administration was not paired with retrieval. These findings indicate that the behavioral outcome of memory retrieval can be pharmacologically switched from extinction to strengthening. The cAMP/protein kinase A (PKA) signaling pathway might be a crucial mechanism determining the fate of memories after recall.

Self administration of oxycodone by adolescent and adult mice affects striatal neurotransmitter receptor gene expression

Illicit use of prescription opioid analgesics (e.g., oxycodone) in adolescence is a pressing public health issue. Our goal was to determine whether oxycodone self administration differentially affects striatal neurotransmitter receptor gene expression in the dorsal striatum of adolescent compared to adult C57BL/6J mice. Groups of adolescent mice (4 weeks old, n=12) and of adult mice (11 weeks old, n=11) underwent surgery during which a catheter was implanted into their jugular veins. After recovering from surgery, mice self administered oxycodone (0.25 mg/kg/infusion) 2 h/day for 14 consecutive days or served as yoked saline controls. Mice were sacrificed within 1h after the last self-administration session and the dorsal striatum was isolated for mRNA analysis. Gene expression was analyzed with real time PCR using a commercially available neurotransmitter receptor PCR array containing 84 genes. We found that adolescent mice self administered less oxycodone than adult mice over the 14 days. Monoamine oxidase A (Maoa) and neuropeptide Y receptor 5 mRNA levels were lower in adolescent mice than in adult mice without oxycodone exposure. Oxycodone self administration increased Maoa mRNA levels compared to controls in both age groups. There was a positive correlation of the amount of oxycodone self administered in the last session or across 14 sessions with Maoa mRNA levels. Gastrin-releasing peptide receptor mRNA showed a significant Drug × Age interaction, with point-wise significance. More genes in the dorsal striatum of adolescents (19) changed in response to oxycodone self administration compared to controls than in adult (4) mice. Overall, this study demonstrates that repeated oxycodone self administration alters neurotransmitter receptors gene expression in the dorsal striatum of adolescent and adult mice.

Gastrin-releasing peptide receptor signaling in the integration of stress and memory

Neuropeptides act as signaling molecules that regulate a range of aspects of brain function. Gastrin-releasing peptide (GRP) is a 27-amino acid mammalian neuropeptide, homolog of the amphibian peptide bombesin. GRP acts by binding to the GRP receptor (GRPR, also called BB2), a member of the G-protein coupled receptor (GPCR) superfamily. GRP produced by neurons in the central nervous system (CNS) plays a role in synaptic transmission by activating GRPRs located on postsynaptic membranes, influencing several aspects of brain function. Here we review the role of GRP/GRPR as a system mediating both stress responses and the formation and expression of memories for fearful events. GRPR signaling might integrate the processing of stress and fear with synaptic plasticity and memory, serving as an important component of the set of neurobiological systems underlying the enhancement of memory storage by aversive information.

The transcriptomic response of mixed neuron-glial cell cultures to 1,25-dihydroxyvitamin d3 includes genes limiting the progression of neurodegenerative diseases

Seasonal or chronic vitamin D deficiency and/or insufficiency is highly prevalent in the human population. Receptors for 1,25-dihydroxyvitamin D3, the hormonal metabolite of vitamin D, are found throughout the brain. To provide further information on the role of this hormone on brain function, we analyzed the transcriptomic profiles of mixed neuron-glial cell cultures in response to 1,25-dihydroxyvitamin D3. 1,25-dihydroxyvitamin D3 treatment increases the mRNA levels of 27 genes by at least 1.9 fold. Among them, 17 genes were related to neurodegenerative and psychiatric diseases, or brain morphogenesis. Notably, 10 of these genes encode proteins potentially limiting the progression of Alzheimer's disease. These data provide support for a role of 1,25-dihydroxyvitamin D3 in brain disease prevention. The possible consequences of circannual or chronic vitamin D insufficiencies on a tissue with a low regenerative potential such as the brain should be considered.

FoxO6 regulates memory consolidation and synaptic function

The FoxO family of transcription factors is known to slow aging downstream from the insulin/IGF (insulin-like growth factor) signaling pathway. The most recently discovered FoxO isoform in mammals, FoxO6, is highly enriched in the adult hippocampus. However, the importance of FoxO factors in cognition is largely unknown. Here we generated mice lacking FoxO6 and found that these mice display normal learning but impaired memory consolidation in contextual fear conditioning and novel object recognition. Using stereotactic injection of viruses into the hippocampus of adult wild-type mice, we found that FoxO6 activity in the adult hippocampus is required for memory consolidation. Genome-wide approaches revealed that FoxO6 regulates a program of genes involved in synaptic function upon learning in the hippocampus. Consistently, FoxO6 deficiency results in decreased dendritic spine density in hippocampal neurons in vitro and in vivo. Thus, FoxO6 may promote memory consolidation by regulating a program coordinating neuronal connectivity in the hippocampus, which could have important implications for physiological and pathological age-dependent decline in memory.

Influence of GRPR and BDNF/TrkB signaling on the viability of breast and gynecologic cancer cells

Neuropeptide and neurotrophin receptors are increasingly important molecular targets in cancer. Scientific findings indicate that compounds blocking gastrin-releasing peptide receptors (GRPR) or tropomyosin receptor kinase (Trk) receptors are likely to have antiproliferative activities against cancer cells. The present study aimed to demonstrate that, in contrast to previous findings, GRPR activation reduces, whereas its blockade increases the viability of breast, ovarian and cervical cancer cell lines. However, consistent with previous studies, Trk inhibition was demonstrated to reduce the viability of these cells. MCF-7 (breast), OVCAR-3 (ovarian) and HeLa (cervical) human cancer cell lines were treated with GRP, the GRPR antagonists RC-3095 and RC-3940-II, brain-derived neurotrophic factor (BDNF) and the Trk antagonist K252α. Cell viability was measured by the MTT assay. Expression of GRPR and BDNF was confirmed with reverse transcription-polymerase chain reaction (RT-PCR). GRP reduced, whereas RC-3940-II enhanced the viability of the three cell lines. Treatment with K252α inhibited the viability of the cell lines, while BDNF increased the viability of OVCAR-3 cells. The results supported the hypothesis that GRPR and BDNF/TrkB signaling regulates cancer cell viability. Most importantly, these findings are the first to demonstrate that GRPR blockade can stimulate, rather than inhibits the viability of breast and gynecologic cancer cell lines.

Neuromedin B and its receptor influence the activity of myometrial primary cells in vitro through regulation of Il6 expression via the Rela/p65 pathway in mice

The neuromedin B receptor (Nmbr) is an important physiological regulator of spontaneous activities and stress responses through different cascades as well as its autocrine and paracrine effects. Previous studies have revealed that neuromedin B (Nmb) and its receptor signal via the Rela (also known as p65)/Il6 pathway in a mouse model of pregnancy. This study investigated the mechanism of Nmbr signaling via the Rela/p65-Il6 pathway and regulation of the concentration of intracellular free calcium ([Ca(2+)](i)) during the onset of labor in primary mouse myometrial cell cultures isolated from mice in term labor. Data demonstrated Nmbr agonist-mediated upregulation of the DNA binding activity of Rela/p65, Il6 expression, and [Ca(2+)](i) in a concentration-dependent manner. Furthermore, a significant correlation was observed between DNA binding activity of Rela/p65 and Il6 expression. Moreover, this up-regulation was blocked by Nmbr and Rela/p65 knockdown, achieved by RNA interference (RNAi) technology. No significant differences were identified in the inhibition of Il6 expression as a result of Nmbr or Rela/p65 knockdown. However, significant differences were observed between the [Ca(2+)](i) in Rela/p65-specific group and that in the Nmbr-specific small interfering RNA (siRNA)-treated groups. These data demonstrated that the Nmb/Nmbr interaction in pregnant myometrial primary cells in vitro predominantly influenced uterine activity through regulation of Il6 expression via the Rela/p65 pathway, although the effects of Nmbr on [Ca(2+)](i) involved several pathways that remain to be elucidated.

Gastrin-releasing peptide receptors in the central nervous system: role in brain function and as a drug target

Neuropeptides acting on specific cell membrane receptors of the G protein-coupled receptor (GPCR) superfamily regulate a range of important aspects of nervous and neuroendocrine function. Gastrin-releasing peptide (GRP) is a mammalian neuropeptide that binds to the GRP receptor (GRPR, BB2). Increasing evidence indicates that GRPR-mediated signaling in the central nervous system (CNS) plays an important role in regulating brain function, including aspects related to emotional responses, social interaction, memory, and feeding behavior. In addition, some alterations in GRP or GRPR expression or function have been described in patients with neurodegenerative, neurodevelopmental, and psychiatric disorders, as well as in brain tumors. Findings from preclinical models are consistent with the view that the GRPR might play a role in brain disorders, and raise the possibility that GRPR agonists might ameliorate cognitive and social deficits associated with neurological diseases, while antagonists may reduce anxiety and inhibit the growth of some types of brain cancer. Further preclinical and translational studies evaluating the potential therapeutic effects of GRPR ligands are warranted.

Inhibition of mTOR by rapamycin in the amygdala or hippocampus impairs formation and reconsolidation of inhibitory avoidance memory

Mammalian target of rapamycin (mTOR), a central regulator of protein synthesis in neurons, has been implicated in synaptic plasticity and memory. Here we show that mTOR inhibition by rapamycin in the basolateral amygdala (BLA) or dorsal hippocampus (DH) impairs both formation and reconsolidation of memory for inhibitory avoidance (IA) in rats. Male Wistar rats received bilateral infusions of vehicle or rapamycin into the BLA or DH before or after IA training or retrieval. Memory retention was tested at different time points after drug infusion. Rapamycin impaired long-term IA retention when given before or immediately after training or retrieval into the BLA. When infused into the DH, rapamycin produced memory impairment when given before training or immediately after retrieval. The impairing effects of post-retrieval rapamycin required memory retrieval and were not reversed by a reminder shock. The results provide the first evidence that mTOR in the BLA and DH might play a role in IA memory reconsolidation.

Behavioural and cellular effects of exogenous amyloid-β peptides in rodents

A better understanding of Alzheimer's disease (AD) and the development of disease modifying therapies are some of the biggest challenges of the 21st century. One of the core features of AD are amyloid plaques composed of amyloid-beta (Aβ) peptides. The first hypothesis proposed that cognitive deficits are linked to plaque-development and transgenic mice have been generated to study this link, thereby providing a good model to develop new therapeutic approaches. Since later it was recognised that in AD patients the cognitive deficit is rather correlated to soluble amyloid levels, consequently, a new hypothesis appeared associating the earliest amyloid toxicity to these soluble species. The purpose of this review is to give a summary of behavioural and cellular data obtained after soluble Aβ peptide administration into rodents' brain, thereby showing that this model is a valid tool to investigate AD pathology when no plaques are present. Additionally, this method offers an excellent, efficient model to test compounds which could act at such early stages of the disease.

Endogenously generated 2-arachidonoylglycerol plays an inhibitory role in bombesin-induced activation of central adrenomedullary outflow in rats

We previously reported the involvement of brain diacylglycerol lipase and cyclooxygenase in intracerebroventricularly (i.c.v.) administered bombesin-induced secretion of noradrenaline and adrenaline from the adrenal medulla in rats. Diacylglycerol can be hydrolyzed by diacylglycerol lipase into 2-arachidonoylglycerol, which may be further hydrolyzed by monoacylglycerol lipase into arachidonic acid, a substrate of cyclooxygenase. 2-Arachidonoylglycerol is a major endocannabinoid, which can inhibit synaptic transmission by presynaptic cannabinoid CB(1) receptors. Released 2-arachidonoylglycerol is rapidly inactivated by uptake into cells and enzymatic hydrolysis. In the present study, we examined the involvement of brain 2-arachidonoylglycerol and its regulatory role in the bombesin-induced central activation of adrenomedullary outflow using anesthetized rats. The elevation of plasma noradrenaline and adrenaline induced by a sub-maximal dose of bombesin (1 nmol/animal, i.c.v.) was reduced by MAFP (monoacylglycerol lipase inhibitor) (0.28 and 0.7 μmol/animal, i.c.v.), JZL184 (selective monoacylglycerol lipase inhibitor) (0.7 and 1.4 μmol/animal, i.c.v.), ACEA (CB(1) receptor agonist) (0.7 and 1.4 μmol/animal, i.c.v.) and AM 404 (endocannabinoid uptake-inhibitor) (80 and 250 nmol/animal, i.c.v.), while AM 251 (CB(1) receptor antagonist) (90 and 180 nmol/animal, i.c.v.) potentiated the response induced by a small dose of bombesin (0.1 nmol/animal, i.c.v.). These results suggest a possibility that 2-arachidonoylglycerol is endogenously generated in the brain during bombesin-induced activation of central adrenomedullary outflow, thereby inhibiting the peptide-induced response by activation of brain CB(1) receptors in rats.

National Science and Technology Institute for Translational Medicine (INCT-TM): advancing the field of translational medicine and mental health

OBJECTIVE

Translational medicine has been described as the integrated application of innovative pharmacology tools, biomarkers, clinical methods, clinical technologies and study designs to improve the understanding of medical disorders. In medicine, translational research offers an opportunity for applying the findings obtained from basic research to every-day clinical applications. The National Science and Technology Institute for Translational Medicine is comprised of six member institutions (Universidade Federal do Rio Grande do Sul, Universidade de São Paulo-Ribeirão Preto, Universidade Federal do Rio de Janeiro, Pontifícia Universidade Católica do Rio Grande do Sul, Universidade Estadual de Santa Catarina and a core facility that serves all centers). The objectives of the project are divided into four areas: Institutional, Research, Human Resources and Technology for the Community and Productive Sector.

METHOD

In this manuscript, we describe some of the approaches used to attain the main objectives of the National Science and Technology Institute for Translational Medicine, which include the development of 1) animal models for bipolar disorder; 2) strategies to investigate neurobehavioral function and cognitive dysfunction associated with brain disorders; 3) experimental models of brain function and behavior, neuropsychiatric disorders, cell proliferation, and cancer; 4) Simulated Public Speaking and 5) Virtual reality simulation for inducing panic disorder and agoraphobia.

CONCLUSION

The main focus of the National Science and Technology Institute for Translational Medicine is the development of more useful methods that allow for a better application of basic research-based knowledge to the medical field.

Cognitive enhancers: focus on modulatory signaling influencing memory consolidation

Biological research has unraveled many of the molecular and cellular mechanisms involved in the formation of long-lasting memory, providing new opportunities for the development of cognitive-enhancing drugs. Studies of drug enhancement of cognition have benefited from the use of pharmacological treatments given after learning, allowing the investigation of mechanisms regulating the consolidation phase of memory. Modulatory systems influencing consolidation processes include stress hormones and several neurotransmitter and neuropeptide systems. Here, we review some of the findings on memory enhancement by drug administration in animal models, and discuss their implications for the development of cognitive enhancers.

Inhibition of phosphodiesterase-4 reverses memory deficits produced by Aβ25-35 or Aβ1-40 peptide in rats

RATIONALE

Cyclic AMP signaling plays an important role in memory loss associated with Alzheimer's disease (AD). However, little is known about whether inhibition of phosphodiesterase-4 (PDE4), which increases intracellular cAMP, reverses β-amyloid peptide (Aβ)-induced memory deficits.

OBJECTIVE

Experiments were performed to demonstrate the effect of the PDE4 inhibitor rolipram on memory impairment produced by Aβ1-40 (Aβ40) or its core fragment Aβ25-35.

METHODS

We tested memory using Morris water-maze and passive avoidance tasks and examined expression of phosphorylated cAMP response-element binding protein (pCREB) in the hippocampus in rats treated with Aβ25-35 or Aβ40 into bilateral CA1 subregions, with or without rolipram administration.

RESULTS

Aβ25-35 (10 μg/side) increased escape latency during acquisition training and decreased swimming time and distance in the target quadrant in the water-maze probe trial; it also decreased 24-h retention in the passive avoidance paradigm. All these were reversed by chronic administration of rolipram (0.5 mg/kg). Similarly, Aβ40 (4 μg/side) produced memory impairment, as demonstrated by decreased retention in passive avoidance; this was also reversed by repeated treatment with rolipram. In addition, rolipram blocked extinction of memory during the 32-day testing period in the passive avoidance test. Further, Aβ40 decreased pCREB expression in the hippocampus, which was also reversed by rolipram; the changes in pCREB were highly correlated with those in memory.

CONCLUSIONS

These results suggest that the PDE4 inhibitor rolipram reverses cognitive deficits associated with AD most likely via increased cAMP/CREB signaling in the hippocampus; PDE4 could be a target for drugs that improve cognition in AD.

Neonatal gastrin-releasing peptide receptor blockade reduces maternal odor preference in rats

Alterations in attachment behavior might play a role in the dysfunction in social behavior displayed by autistic infants. Here we show that neonatal gastrin-releasing peptide receptor (GRPR) blockade induces a reduction in maternal odor preference, a task involving attachment behavior, in infant rats. These findings provide the first evidence that the GRPR regulates odor preference, supporting the view that the GRPR is involved in attachment and social behaviors.

Effect of a gastrin-releasing peptide receptor antagonist and a proton pump inhibitor association in an animal model of gastritis

It has been proposed that reactive oxygen species play a causative role of gastric mucosal damage induced by increased gastric secretion. Gastrin-releasing peptide is a typical neuropeptide that stimulates acid secretion by release of gastrin. In the present work we have investigated the mechanism of indomethacin (IDM)-induced gastric ulcer caused by ROS and determined the effects of a selective gastrin-releasing peptide receptor antagonist, RC-3095, alone and in association with omeprazole (OM) and compared it with an established antioxidant compound N-acetyl cysteine (NAC). Adult male Wistar rats were pre-treated for 7 days with OM, RC-3095, NAC, both drugs and water (control). The animals were then submitted to fasting for 24h; IDM was administered. Rats were killed 6h after that and the stomachs were used for evaluation of macroscopic damage and oxidative stress parameters. Our results showed that IDM increased mitochondrial superoxide production; OM and RC-3095 alone did not prevent such effect, but the combination of these drugs was effective. TBARS assay revealed that IDM-induced lipid peroxidation in gastric tissue and that OM and RC-3095, alone or in combination, prevented this effect with superior action that NAC. Finally, we verified that IDM increased protein carbonyl content and that this effect was prevented RC-3095, alone or in combination with OM, being similar to standard antioxidant. The present results support the view that, besides the inhibition of acid secretion, the protective effects exerted by OM and RC-3095 against IDM-induced gastric damage can be ascribed to a reduction of gastric oxidative injury.

Effects of the LHRH antagonist Cetrorelix on the brain function in mice

The decapeptide Cetrorelix, an LHRH antagonist, inhibits gonadotropin and sex steroid secretion. Cetrorelix is used for IVF-ET procedures and for the treatment of patients with prostate carcinoma, benign prostatic hyperplasia, endometriosis, leiomyomas and, ovarian cancer. However little is known about the effects of Cetrorelix on the brain function. In the present work the influence of Cetrorelix on different aspects of the brain function was studied following its administration into the lateral brain ventricle in mice. The effects tested included the impairment of the consolidation of a passive avoidance reflex caused by beta-amyloid 25-35, anxiolytic action in the plus-maze, antidepressive action in a forced swimming test and a tail suspension test and open-field behavior. In the passive avoidance test, beta-amyloid 25-35 administered immediately after the learning trial impaired the consolidation of passive avoidance learning. Cetrorelix fully blocked the impairment of the consolidation of passive avoidance learning when given icv 30 min following beta-amyloid 25-35 administration. If beta-amyloid 25-35 and Cetrorelix icv were given simultaneously, the Cetrorelix attenuated, but did not block the action of the beta-amyloid 25-35. Cetrorelix elicited anxiolytic action in the plus-maze, depending on the dose used. In the forced swimming and tail suspension tests, Cetrorelix demonstrated antidepressive-like action. Concerning open-field behavior, Cetrorelix displayed no action on locomotion, rearing or grooming. The results demonstrate that Cetrorelix affects brain function: and is able to correct the impairment of the memory consolidation caused by beta-amyloid 25-35. Cetrorelix also elicits anxiolytic and antidepressive action, but it does not influence the open-field activity. Further experimental work with Cetrorelix is necessary, but the results imply the possible merit of a clinical trial with Cetrorelix in patients with anxiety, depression and Alzheimer's disease.

Phosphoinositide 3-kinase is required for bombesin-induced enhancement of fear memory consolidation in the hippocampus

Increasing evidence indicates that the neuronal gastrin-releasing peptide-preferring bombesin receptor (GRPR) is a key molecular regulator of fear memory formation. However, the downstream signaling events remain poorly understood. The protooncogene product phosphoinositide 3-kinase (PI3K) has been implicated in regulating memory formation, as well as in mediating cellular responses to GRPR activation in glioma and neuroblastoma cells. We show here that GRPR modulation of fear memory consolidation in the rat hippocampus requires PI3K activation. Male Wistar rats received bilateral infusions of the GRPR agonist bombesin (BB) or the PI3K inhibitor LY294002 into the CA1 region of the dorsal hippocampus immediately after inhibitory avoidance (IA) conditioning. BB enhanced, whereas LY294002 impaired, IA memory retention. The BB-induced memory enhancement was blocked by coinfusion of either a GRPR antagonist or LY294002. These findings provide the first evidence suggesting that PI3K signaling is required for GRPR regulation of CNS function.