Adult Rat Hippocampus Research Articles

481 Subacute Cell Specific Gene Expression Changes After Experimental TBI Suggest Target Genes for Cognitive Dysfunction

INTRODUCTION: Approximately 1.8 million Americans suffer from traumatic brain injury (TBI) each year, many of whom develop persistent cognitive difficulties. Understanding gene expression changes in cell types important for cognitive function may provide insight for therapeutic targets. METHODS: The dentate gyrus was dissected from the hippocampi of adult Sprague Dawley rats three weeks after either control or moderate lateral fluid percussion injury. Nuclei were isolated, the RNA was extracted, and sequenced using 10X Genomics technology. The RNA sequences were mapped to the rat genome (Rnor 6.0), quantified, and their expression normalized. Clustering of nuclei based on their gene expression profiles was done using Seurat (v4.0.1; R version 4.0.5). The granule cell cluster from each sample was identified based on expression of Prox1 and Rfx3, along with other neuronal markers. Genes with significant negatively correlated expressions between conditions were identified as differentially expressed and their functions were explored through Gene Ontology (GO). RESULTS: We identified a total of 14819 genes expressed in the granule cell clusters. Of these, 85 were differentially expressed. We identified twelve statistically significant biological processes using GO terms. GO terms with implications for cognitive function included: memory (p=0.000191, GO:0007613), negative regulation of amyloid-beta formation (p=0.000192, GO:1902430), and protein-lipid complex assembly (p=0.000192, GO:0065005). Statistically significant genes of interest associated with GO terms were under-expressed in the TBI condition: Apoe (p=0.00039), Atad1 (p=0.000013), Cpe (p=0.000438), and Dbn1 (0.002505). CONCLUSION: Three weeks after experimental TBI, hippocampal dentate granule cells under-express genes important for neurotransmitter receptor trafficking and neuronal survival. Future studies with cell-specific methodologies may yield targets for therapeutic strategies to improve cognitive dysfunction after TBI.

Ellagic acid and allopurinol decrease H2O2 concentrations, epileptiform activity and astrogliosis after status epilepticus in the hippocampus of adult rats.

Status epilepticus (SE) can result in an overproduction of hydrogen peroxide (H2O2), which contributes to oxidative stress and brain injury during different phases of epileptogenesis and seizures. The purpose of this study was to evaluate the effects of ellagic acid and allopurinol administered after SE on H2O2 concentrations, electrical activity and GFAP immunoreactivity in the hippocampus of rats evaluated on Day 18 after SE. H2O2 levels were measured using an online technique with high temporal resolution and simultaneous electrical activity recording. For this purpose, the lateral ventricles of male Wistar rats (200-250g) were injected with pilocarpine (2.4mg/2µl) to induce SE. After SE, rats were injected with ellagic acid (50mg/kg i.p., and two additional doses at 24 and 48h) or allopurinol (50mg/kg i.p., single dose). Administration of ellagic acid or allopurinol after SE significantly reduced the H2O2 concentrations and decreased the presence of epileptiform activity and GFAP immunoreactivity in the hippocampus 18days after SE. In conclusion, the administration of antioxidants potentially reduces oxidative stress, which indicates the possible attenuation of the neurobiological consequences after SE.

N-Acetylcysteine and Aripiprazole Improve Social Behavior and Cognition and Modulate Brain BDNF Levels in a Rat Model of Schizophrenia.

Treatment of negative symptoms and cognitive disorders in patients with schizophrenia is still a serious clinical problem. The aim of our study was to compare the efficacy of chronic administration of the atypical antipsychotic drug aripiprazole (7-{4-[4-(2,3-dichlorophenyl)-1-piperazinyl] butoxy}-3,4-dihydro-2(1H)-quinolinone; ARI) and the well-known antioxidant N-acetylcysteine (NAC) both in alleviating schizophrenia-like social and cognitive deficits and in reducing the decreases in the levels of the brain-derived neurotrophic factor (BDNF) in the prefrontal cortex (PFC) and hippocampus (HIP) of adult Sprague-Dawley rats, that have been induced by chronic administration of the model compound L-buthionine-(S, R)-sulfoximine (BSO) during the early postnatal development (p5–p16). ARI was administered at doses of 0.1 and 0.3 mg/kg while NAC at doses of 10 and 30 mg/kg, alone or in combination. Administration of higher doses of ARI or NAC alone, or co-treatment with lower, ineffective doses of these drugs significantly improved social and cognitive performance as assessed in behavioral tests. Both doses of NAC and 0.3 mg/kg of ARI increased the expression of BDNF mRNA in the PFC, while all doses of these drugs and their combinations enhanced the levels of BDNF protein in this brain structure. In the HIP, only 0,3 mg/kg ARI increased the levels of both BDNF mRNA and its protein. These data show that in the rat BSO-induced neurodevelopmental model of schizophrenia, ARI and NAC differently modulated BDNF levels in the PFC and HIP.

Subchronic PCP effects on DNA methylation and protein expression of NMDA receptor subunit genes in the prefrontal cortex and hippocampus of female rats.

N-methyl-d-aspartate receptor (NMDAR) dysfunction is implicated in schizophrenia, and NMDAR antagonists, such as phencyclidine (PCP), can induce behaviours that mimic aspects of the disorder. We investigated DNA methylation of Grin1, Grin2a and Grin2b promoter region and NR1 and NR2 protein expression in the prefrontal cortex (PFC) and hippocampus of adult female Lister-hooded rats following subchronic PCP (scPCP) administration. We also determined whether any alterations were tissue-specific. Rats were divided into two groups that received vehicle (0.9% saline) or 2 mg/kg PCP twice a day for 7 days (n = 10 per group). After behavioural testing (novel object recognition), to confirm a cognitive deficit, brains were dissected and NMDAR subunit DNA methylation and protein expression were analysed by pyrosequencing and ELISA. Line-1 methylation was determined as a measure of global methylation. Data were analysed using Student's t-test and Pearson correlation. The scPCP administration led to Grin1 and Grin2b hypermethylation and reduction in NR1 protein in both PFC and hippocampus. No significant differences were observed in Line-1 or Grin2a methylation and NR2 protein. The scPCP treatment resulted in increased DNA methylation at promoter sites of Grin1 and Grin2b NMDAR subunits in two brain areas implicated in schizophrenia, independent of any global change in DNA methylation, and are similar to our observations in a neurodevelopmental animal model of schizophrenia - social isolation rearing post-weaning. Moreover, these alterations may contribute to the changes in protein expression for NMDAR subunits demonstrating the potential importance of epigenetic mechanisms in schizophrenia.

Deficits of Learning and Spatial Memory are Associated with Increased Pyknosis of Pyramidal Neurons of the Hippocampus of Adult Rats with Chronic Hydrocephalus


 Background: The hippocampus is the brain's center for the consolidation of short-term and spatial memory that enables navigation. Hippocampal injury occurs in hydrocephalus and is associated with loss of memory.
 Objective: We assessed pyknotic changes in kaolin-induced chronic hydrocephalus in adult rats using qualitative and quantitative means, and related these to memory deficits in the rats.
 Methods: Adult rats were randomly divided into control and experimental groups. Hydrocephalus was induced by intracisternal injection of 0.1ml sterile kaolin suspension for 6weeks. Control rats received sham injections. Spatial memory was assessed with the Morris water maze test. Coronal sections of the brains were grouped into either mild or moderate hydrocephalus and then stained with H&E and cresyl violet stains. Thus, there were three groups: control, mild hydrocephalus and moderate hydrocephalus (n=10), respectively.
 Results: Shrinking and thinning of the hippocampal tissue, distortion of the pyramidal layer and pyknotic cells were observed in the CA1 and CA3 regions of the hydrocephalic rats. The pyknotic indices in the mild hydrocephalic rat (Cornus Ammonis, CA) CA1, CA2, CA3 (54.30±1.38; 27.62±0.83; 57.61±0.74) and moderate hydrocephalic rat CA1, CA2, CA3 (48.18±0.67; 32.00±0.84; 42.41±1.19) regions were significantly increased compared to the controls' CA1, CA2, CA3 (12.14±0.56; 9.21±0.36; 13.04±0.59).
 Conclusion: Chronic hydrocephalus in adult rats was associated with cell death in all the regions of the hippocampus, irrespective of the degree of ventricular enlargement. The extent of cell death corresponded with the severity of learning and memory deficits.
 Background: The hippocampus is the center of the brain for the consolidation of short-term memory and spatial memory that enables navigation. Hippocampal damage occurs in hydrocephalus and is associated with memory loss.
 Objective: We assessed pyknotic changes in chronic kaolin-induced hydrocephalus in adult rats using qualitative and quantitative means, and related them to memory deficits in rats.
 Methods: Adult rats were randomly assigned to control and experimental groups. Hydrocephalus was induced by intracisternal injection of 0.1 ml of sterile kaolin suspension for 6 weeks. Control rats received sham injections. Spatial memory was assessed by the Morris water maze test. Coronal sections of brains were grouped into mild or moderate hydrocephalus and then stained with H&E and cresyl violet. There were therefore three groups: control, mild hydrocephalus and moderate hydrocephalus (n=10), respectively.
 RESULTS: Shrinking and thinning of hippocampal tissue, distortion of the pyramidal layer, and pyknotic cells were observed in the CA1 and CA3 regions of hydrocephalic rats. The pyknotic indices in the CA1, CA2 and CA3 regions of mild hydrocephalic rats (Cornus Ammonis, CA) (54.30±1.38; 27.62±0.83; 57.61±0.74) and hydrocephalic rats moderate CA1, CA2 and CA3 (48.18±0.67; 32.00±0.84; 42.41±1.19) were significantly increased compared to the CA1, CA2, CA3 regions of controls (12.14±0.56; 9.21±0.36; 13.04±0.59).
 Conclusion: Chronic hydrocephalus in adult rats was associated with cell death in all regions of the hippocampus, regardless of the degree of ventricular enlargement. The extent of cell death corresponded to the severity of learning and memory deficits.
 Key words: Chronic hydrocephalus, hippocampus, adult rats, memory, pyknotic cells.
 
 Keywords: Adult rats; Chronic hydrocephalus; hippocampus; memory; pyknotic cells.

Histopathological, Immunohistochemical, And Molecular Alterations In Brain Tissue And Submandibular Salivary Gland Of Atrazine-Induced Toxicity In Male Rats.

Atrazine (ATZ) is herbicide that has been widely used for different crops. This extensive use has resulted in severe deleterious effects in different species. In this work, we investigated the potentially harmful effect of atrazine herbicide on the brain and submandibular salivary gland. Our investigation was carried out on 20 adult male albino rats that were equally divided into two groups. The first group received distilled water as control, while the second group received ATZ at 200mg/kg body weight/ day via stomach gavage for 30 successive days of the experiment; the oral LD50 for ATZ is 3090mg/kg. Our findings revealed the ability of ATZ to cause damage to the cerebrum, hippocampus, and submandibular salivary gland. This damage resulted from the induced oxidative stress, which was indicated by a significant elevation in malondialdehyde (MDA) concentration, DNA fragmentation, tumor necrotic factor-alpha (TNF-α) expression, with a significant decrease in reduced glutathione (GSH) level and reduction of B cell lymphoma 2 (BCL2), dopamine receptor D1 (Drd1), cAMP-responsive element-binding protein 1 (Creb1) genes expression after ATZ exposure. Moreover, degeneration of cells, cytoplasmic vacuolation, congestion of blood vessels, a strong immune reaction to caspase 3, and negligible immune expression of a glial fibrillary acidic protein (GFAP) were also noticed in the ATZ-treated group. We concluded that ATZ induces oxidative stress and has a toxic and apoptotic effects on the cerebrum, hippocampus, and salivary gland of adult male albino rats.

Administration of Kainic Acid Differentially Alters Astrocyte Markers and Transiently Enhanced Phospho-Tau Level in Adult Rat Hippocampus

Administration of Kainic Acid Differentially Alters Astrocyte Markers and Transiently Enhanced Phospho-Tau Level in Adult Rat Hippocampus

Prolonged alprazolam treatment modulates components of glutamatergic signaling in hippocampus of adult male Wistar rats

Prolonged alprazolam treatment modulates components of glutamatergic signaling in hippocampus of adult male Wistar rats

Prenatal Iron Deficiency and Choline Supplementation Interact to Epigenetically Regulate Jarid1b and Bdnf in the Rat Hippocampus into Adulthood.

Early-life iron deficiency (ID) causes long-term neurocognitive impairments and gene dysregulation that can be partially mitigated by prenatal choline supplementation. The long-term gene dysregulation is hypothesized to underlie cognitive dysfunction. However, mechanisms by which iron and choline mediate long-term gene dysregulation remain unknown. In the present study, using a well-established rat model of fetal-neonatal ID, we demonstrated that ID downregulated hippocampal expression of the gene encoding JmjC-ARID domain-containing protein 1B (JARID1B), an iron-dependent histone H3K4 demethylase, associated with a higher histone deacetylase 1 (HDAC1) enrichment and a lower enrichment of acetylated histone H3K9 (H3K9ac) and phosphorylated cAMP response element-binding protein (pCREB). Likewise, ID reduced transcriptional capacity of the gene encoding brain-derived neurotrophic factor (BDNF), a target of JARID1B, associated with repressive histone modifications such as lower H3K9ac and pCREB enrichments at the Bdnf promoters in the adult rat hippocampus. Prenatal choline supplementation did not prevent the ID-induced chromatin modifications at these loci but induced long-lasting repressive chromatin modifications in the iron-sufficient adult rats. Collectively, these findings demonstrated that the iron-dependent epigenetic mechanism mediated by JARID1B accounted for long-term Bdnf dysregulation by early-life ID. Choline supplementation utilized a separate mechanism to rescue the effect of ID on neural gene regulation. The negative epigenetic effects of choline supplementation in the iron-sufficient rat hippocampus necessitate additional investigations prior to its use as an adjunctive therapeutic agent.

Effects of oral ingestion of hyoscyamine from Daturastramonium seeds on the hippocampus in adult Wistar rats (Rattusnorvegicus)

The study aimed to evaluate the effects of oral ingestion of hyoscyamine fraction of Daturastramonium seeds on the hippocampus in adult Wistar rats. Fresh seeds of D. stramonium were procured and fractionated using high-performance liquid chromatography (HPLC). Twenty-four healthy adult Wistar rats weighed 230±0.50 grams, were procured and divided equally into four groups for the experiment. The group one received an equivalent bodyweight of normal saline, while three other groups received 200, 400 and 800 mg/kgbwt of hyoscyamine fraction of D. stramonium respectively for three weeks. At the end of the experiment, the animals were subjected to memory test using Morris water maze (MWM) and Novel object recognition test (NORT) test paradigms. The data obtained were expressed as mean ± SEM and repeated measures ANOVA with Fisher’s multiple comparisons post-hoc tests were used to obtain mean differences using Minitab 17 (LLC., U.K.) statistical package software. P < 0.05 was considered statistically significant. There was a statistically significant increase in the exploration time (p = 0.031) and escape latency period (p < 0.001) in the novel object recognition and Morris water maze test between the groups in the treated compared to the control group. The CA3 region of the treated group showed significant neuronal lesions, cytoplasmic vacuolations, pyknosis and necrosis. . In conclusion, exposure to hyoscyamine fraction of D.stramonium at adulthood impaired memory in Wistar rats.

Study of Anticonvulsant Effects of Carbamazepine During Epileptic Process by Unilateral Kindling of CA1 Dorsal Hippocampus in Adult Male Rats

Study of Anticonvulsant Effects of Carbamazepine During Epileptic Process by Unilateral Kindling of CA1 Dorsal Hippocampus in Adult Male Rats

Effects of traumatic stress in adolescence on PTSD-like behaviors, dendrite development, and H3K9me2/BDNF expression in the amygdala of male rats

Early detrimental experiences increase the risk of psychiatric disorders, including posttraumatic stress disorder (PTSD). In a previous experiment, we demonstrated that traumatic stress in adolescence triggers changes in the expression of the epigenetic marker H3K9me2 in the hippocampus and prefrontal cortex of adolescent and adult rats, which suppresses transcription of the brain-derived neurotrophic factor (Bdnf) gene that promotes dendrite development and synaptic growth. However, corresponding changes in the amygdala in response to traumatic stress in early life have not yet been fully elucidated. In the current study, we used the inescapable foot shock (IFS) procedure to establish a PTSD model. Half an hour after the end of electric shocks, intraperitoneal injection of the G9a enzyme inhibitor Unc0642, a small molecule inhibitor of EHMT2 that can decrease H3K9me2 expression, was applied to reverse the corresponding epigenetic changes. Exploratory behaviors, anxiety-like behavior, social communication ability, spatial exploration and memory were determined using the open field test (OFT), elevated plus maze (EPM) test, three-chamber sociability test (SIT), Morris water maze (MWM) test, and Y maze test (YMZ), respectively. Additionally, the levels of H3K9me2 and BDNF were measured by quantitative reverse transcription-polymerase chain reaction (qPCR) and Western blotting. Furthermore, neuronal development was examined using Golgi staining. The results showed that the IFS procedure induced anxiety-like and depression-like behaviors, social skills dysfunction, and spatial exploration and memory disorders. It also decreased the mRNA expression of BDNF and BDNF and increased the expression of H3K9me2 in the amygdala. More importantly, compared to unstressed animals, traumatic stress during adolescence induced dendrite maldevelopment in adolescent and adult rats. In summary, the present study indicates that early-life stress alters the epigenetic marker expression of H3K9me2 and decreases levels of BDNF in the amygdala, resulting in dendrite maldevelopment and a higher risk of mental disorders.

Metaplastic Reinforcement of Long-Term Potentiation in Hippocampal Area CA2 by Cholinergic Receptor Activation.

Hippocampal CA2, an inconspicuously positioned area between the well-studied CA1 and CA3 subfields, has captured research interest in recent years because of its role in social memory formation. However, the role of cholinergic inputs to the CA2 area for the regulation of synaptic plasticity remains to be fully understood. We show that cholinergic receptor activation with the nonselective cholinergic agonist, carbachol (CCh), triggers a protein synthesis-dependent and NMDAR-independent long-term synaptic depression (CCh-LTD) at entorhinal cortical (EC)-CA2 and Schaffer collateral (SC)-CA2 synapses in the hippocampus of adult male Wistar rats. The activation of muscarinic acetylcholine receptors (mAChRs) is critical for the induction of CCh-LTD with the results suggesting an involvement of M3 and M1 mAChRs in the early facilitation of CCh-LTD, while nicotinic AChR activation plays a role in the late maintenance of CCh-LTD at CA2 synapses. Remarkably, we find that CCh priming lowers the threshold for the subsequent induction of persistent long-term potentiation (LTP) of synaptic transmission at EC-CA2 and the plasticity-resistant SC-CA2 pathways. The effects of such a cholinergic-dependent synaptic depression on subsequent LTP at EC-CA2 and SC-CA2 synapses have not been previously explored. Collectively, the results demonstrate that CA2 synaptic learning rules are regulated in a metaplastic manner, whereby modifications triggered by prior cholinergic stimulation can dictate the outcome of future plasticity events. Moreover, the reinforcement of LTP at EC inputs to CA2 following the priming stimulus coexists with concurrent sustained CCh-LTD at the SC-CA2 pathway and is dynamically scaled by modulation of SC-CA2 synaptic transmission.SIGNIFICANCE STATEMENT The release of the neuromodulator acetylcholine is critically involved in processes of hippocampus-dependent memory formation. Cholinergic afferents originating in the medial septum and diagonal bands of Broca terminating in the hippocampal area CA2 might play an important role in the modulation of area-specific synaptic plasticity. Our findings demonstrate that cholinergic receptor activation induces an LTD of synaptic transmission at entorhinal cortical- and Schaffer collateral-CA2 synapses. This cholinergic activation-mediated LTD displays a bidirectional metaplastic switch to LTP on a future timescale. This suggests that such bidirectional synaptic modifications triggered by the dynamic modulation of tonic cholinergic receptor activation may support the formation of CA2-dependent memories given the increased hippocampal cholinergic tone during active wakefulness observed in exploratory behavior.

Perinatal exposure to a glyphosate-based herbicide causes dysregulation of dynorphins and an increase of neural precursor cells in the brain of adult male rats

Glyphosate, the most used herbicide worldwide, has been suggested to induce neurotoxicity and behavioral changes in rats after developmental exposure. Studies of human glyphosate intoxication have reported adverse effects on the nervous system, particularly in substantia nigra (SN). Here we used matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) to study persistent changes in peptide expression in the SN of 90-day-old adult male Wistar rats. The animals were perinatally exposed to 3 % GBH (glyphosate-based herbicide) in drinking water (corresponding to 0.36 % of glyphosate) starting at gestational day 5 and continued up to postnatal day 15 (PND15). Peptides are present in the central nervous system before birth and play a critical role in the development and survival of neurons, therefore, observed neuropeptide changes could provide better understanding of the GBH-induced long term effects on SN. The results revealed 188 significantly altered mass peaks in SN of animals perinatally exposed to GBH. A significant reduction of the peak intensity (P < 0.05) of several peptides from the opioid-related dynorphin family such as dynorphin B (57 %), alpha-neoendorphin (50 %), and its endogenous metabolite des-tyrosine alpha-neoendorphin (39 %) was detected in the GBH group. Immunohistochemical analysis confirmed a decreased dynorphin expression and showed a reduction of the total area of dynorphin immunoreactive fibers in the SN of the GBH group. In addition, a small reduction of dynorphin immunoreactivity associated with non-neuronal cells was seen in the hilus of the hippocampal dentate gyrus. Perinatal exposure to GBH also induced an increase in the number of nestin-positive cells in the subgranular zone of the dentate gyrus. In conclusion, the results demonstrate long-term changes in the adult male rat SN and hippocampus following a perinatal GBH exposure suggesting that this glyphosate-based formulation may perturb critical neurodevelopmental processes.

Effects of early-life stress and sex on blood-brain barrier permeability and integrity in juvenile and adult rats.

Early-life stress (ELS) is considered a relevant etiological factor for neurodegenerative and mental disorders. In the present study, we hypothesized that ELS may persistently and sex dependently influence blood-brain barrier (BBB) integrity and function during critical periods of brain development and consequently determine susceptibility to and sex-related prevalence of chronic diseases in adult life. We used the maternal separation (MS) procedure in rats to model ELS and evaluated BBB permeability and gene expression of selected tight junction (TJ) proteins, glucose transporter type 1 (Slc2a1) and aquaporin 4 (Aqp4) in the medial prefrontal cortex (mPFC), dorsal striatum (dSTR) and hippocampus of juvenile and adult rats. Serum concentrations of a peripheral marker of BBB function (S100β) and proinflammatory cytokines were also assessed. We observed developmental sealing of the BBB and sex differences in the permeability of the BBB and the mRNA expression of TJ proteins and Slc2a1. Adult females showed lower BBB permeability and higher levels of Cldn3, Cldn5, Ocln, and Slc2a1 in the mPFC and dSTR than males. MS temporarily increased BBB permeability in the dSTR of juvenile males and affected mRNA expression of the majority of studied proteins related to BBB function in age-, region- and sex-dependent manners. Additionally, MS sex dependently decreased serum S100β levels and did not affect proinflammatory cytokine concentrations. In general, our study did not reveal a clear or strong negative effect of MS on BBB integrity. However, the results suggest that ELS may induce adaptive/maladaptive changes or compensatory mechanisms within the BBB of unknown yet consequences.

Neonatal Maternal Separation Modifies Proteostasis Marker Expression in the Adult Hippocampus

Exposure to early-life stress (ELS) can persistently modify neuronal circuits and functions, and contribute to the expression of misfolded and aggregated proteins that are hallmarks of several neurodegenerative diseases. The healthy brain is able to clear dysfunctional proteins through the ubiquitin-proteasome system (UPS) and the autophagy-lysosomal pathway (ALP). Accumulating evidence indicates that impairment of these pathways contributes to enhanced protein aggregation and neurodegeneration. While stress is a known precipitant of neurological decline, few specific mechanistic links underlying this relationship have been identified. We hypothesized that neonatal maternal separation (MatSep), a well-established model of ELS, has the ability to alter the levels of UPS and ALP components in the brain, and thus has the potential to disrupt proteostasis. The expression of proteostasis-associated protein markers was evaluated by immunoblotting in the hippocampus and cortex of adult Wistar rats that were previously subjected to MatSep. We observed multiple sex- and MatSep-specific changes in the expression of proteins in the ALP, mitophagy, and UPS pathways, particularly in the hippocampus of adult animals. In contrast, MatSep had limited influence on proteostasis marker expression in the cortex of adult animals. Our results indicate that MatSep can selectively modify the intracellular protein degradation machinery in ways that may impact the development and progression of neurodegenerative disease.

Aversive Learning Deficits and Depressive-Like Behaviors Are Accompanied by an Increase in Oxidative Stress in a Rat Model of Fetal Alcohol Spectrum Disorders: The Protective Effect of Rapamycin.

Fetal alcohol spectrum disorders (FASDs) are one of the most common consequences of ethanol exposure during pregnancy. In adulthood, these disorders can be manifested by learning and memory deficits and depressive-like behavior. Ethanol-induced oxidative stress may be one of the factors that induces FASD development. The mammalian target of the Rapamycin (mTOR) signaling pathway that acts via two distinct multiprotein complexes, mTORC1 and mTORC2, can affect oxidative stress. We investigated whether mTOR-dependent or mTOR-independent mechanisms are engaged in this phenomenon. Thus, Rapamycin—a selective inhibitor of mTORC1, Torin-2—a non-selective mTORC1/mTORC2 inhibitor, and FK-506—a drug that impacts oxidative stress in an mTOR-independent manner were used. Behavioral tests were performed in adult (PND60-65) rats using a passive avoidance (PA) task (aversive learning and memory) and forced swimming test (FST) (depressive-like behaviors). In addition, the biochemical parameters of oxidative stress, such as lipid peroxidation (LPO), as well as apurinic/apyrimidinic (AP)-sites were determined in the hippocampus and prefrontal cortex in adult (PND65) rats. The rat FASD model was induced by intragastric ethanol (5 g/kg/day) administration at postnatal day (PND)4–9 (an equivalent to the third trimester of human pregnancy). All substances (3 mg/kg) were given 30 min before ethanol. Our results show that neonatal ethanol exposure leads to deficits in context-dependent fear learning and depressive-like behavior in adult rats that were associated with increased oxidative stress parameters in the hippocampus and prefrontal cortex. Because these effects were completely reversed by Rapamycin, an mTORC1 inhibitor, this outcome suggests its usefulness as a preventive therapy in disorders connected with prenatal ethanol exposure.

Neonatal maternal separation affects metabotropic glutamate receptor 5 expression and anxiety-related behavior of adult rats.

Exposure to early life stress leads to long-term neurochemical and behavioral alterations. Stress-induced psychiatric disorders, such as depression, have recently been linked to dysregulation of glutamate signaling, mainly via its postsynaptic receptors. The role of metabotropic glutamate receptor 5 (mGluR5) in stress-induced psychopathology has been the target of several studies in humans. In rodents, blockade of mGluR5 produces antidepressant-like actions, whereas mice lacking mGluR5 exhibit altered anxiety-like behaviors and learning. In this study, we used well-known rodent models of early life stress based on mother-infant separation during the first 3 weeks of life in order to examine the effects of neonatal maternal separation on mGluR5 expression and on anxiety-related behavior in adulthood. We observed that brief (15 min) neonatal maternal separation, but not prolonged (3h), induced increases in mGluR5 mRNA and protein expression levels in medial prefrontal cortex and mGluR5 protein levels in dorsal, but not ventral, hippocampus of adult rat brain. Behavioral testing using the open-field and the elevated-plus maze tasks showed that brief maternal separations resulted in increased exploratory and decreased anxiety-related behavior, whereas prolonged maternal separations resulted in increased anxiety-related behavior in adulthood. The data indicate that the long-lasting effects of neonatal mother-offspring separation on anxiety-like behavior and mGluR5 expression depend on the duration of maternal separation and suggest that the increased mGluR5 receptors in medial prefrontal cortex and hippocampus of adult rats exposed to brief neonatal maternal separations may underlie their heightened ability to cope with stress.

Intrinsic Aerobic Capacity Affects Hippocampal pAkt and HSP72 Response to an Acute High Fat Diet and Heat Treatment in Rats.

Background:Aerobic capacity is associated with metabolic, cardiovascular, and neurological health. Low-capacity runner (LCR) rats display low aerobic capacity, metabolic dysfuction, and spatial memory deficits. A heat treatment (HT) can improve metabolic dysfunction in LCR peripheral organs after high fat diet (HFD). Little is known about metabolic changes in the brains of these rats following HT.Objective:Our objective was to examine the extent to which high or low aerobic capacity impacts Akt (a protein marker of metabolism) and heat shock protein 72 (HSP72, a marker of heat shock response) after HFD and HT in hippocampus.Methods:We measured phosphorylated Akt (pAkt) in the striatum and hippocampus, and HSP72 in the hippocampus, of HFD-fed and chow-fed LCR and high-capacity runner (HCR) rats with and without HT.Results:pAkt was lower in the hippocampus of chow-fed LCR than HCR rats. HFD resulted in greater pAkt in LCR but not HCR rats, but HT resulted in lower pAkt in the LCR HFD group. HSP72 was greater in both HCR and LCR rat hippocampus after HT. The HFD blunted this effect in LCR compared to HCR hippocampus.Conclusion:The abnormal phosphorylation of Akt and diminished HSP response in the hippocampus of young adult LCR rats might indicate early vulnerability to metabolic challenges in this key brain region associated with learning and memory.

Neonatal Exposure to Bacterial Lipopolysaccharide Affects Behavior and Expression of Ionotropic Glutamate Receptors in the Hippocampus of Adult Rats after Psychogenic Trauma.

According to the two-hit hypothesis of psychoneuropathology formation, infectious diseases and other pathological conditions occurring during the critical periods of early ontogenesis disrupt normal brain development and increase its susceptibility to stress experienced in adolescence and adulthood. It is believed that these disorders are associated with changes in the functional activity of the glutamatergic system in the hippocampus. Here, we studied expression of NMDA (GluN1, GluN2a, GluN2b) and AMPA (GluA1, GluA2) glutamate receptor subunits, as well as glutamate transporter EAAT2, in the ventral and dorsal regions of the hippocampus of rats injected with LPS during the third postnatal week and then subjected to predator stress (contact with a python) in adulthood. The tests were performed 25 days after the stress. It was found that stress altered protein expression in the ventral, but not in the dorsal hippocampus. Non-stressed LPS-treated rats displayed lower levels of the GluN2b protein in the ventral hippocampus vs. control animals. Stress significantly increased the content of GluN2b in the LPS-treated rats, but not in the control animals. Stress also affected differently the exploratory behavior of LPS-injected and control rats. Compared to the non-stressed animals, stressed control rats demonstrated a higher locomotor activity during the 1st min of the open field test, while the stressed LPS-injected rats displayed lower locomotor activity than the non-stressed rats. In addition, LPS-treated stressed and non-stressed rats spent more time in the open arms of the elevated plus maze and demonstrated reduced blood levels of corticosterone. To summarize the results of our study, exposure to bacterial LPS in the early postnatal ontogenesis affects the pattern of stress-induced changes in the behavior and hippocampal expression of genes coding for ionotropic glutamate receptor subunits after psychogenic trauma suffered in adulthood.