Prenatal melamine exposure impairs cognitive flexibility and hippocampal synaptic plasticity in adolescent and adult female rats

Subchronic cyanuric acid treatment impairs spatial flexible behavior in female adolescent rats through depressing GluN2B-dependent neuronal and synaptic function

Subchronic exposure to cyanuric acid (CA) and its structural analogue melamine induces long-term effects on brain and behavior in male rodents. To examine if this exposure induced negative effects on cognitive function in females, we examined the behavioral performance and further attempted to investigate synaptic and neuronal function. CA was intraperitoneal treated with 20 or 40 mg/kg/day to adolescent female rats for 4 consecutive weeks. Multiple behavioral tests were employed to assess spatial cognition, learning strategy, locomotion and motivation. Hippocampal synaptic function at Schaffer collaterals-CA1 synapses and excitatory postsynaptic currents (EPSCs) in CA1 pyramidal neurons was evaluated. Meanwhile, the glutamate transport inhibitor DL-threo-β-benzyloxyaspartate (DL-TBOA) was infused into hippocampal CA1 region to certify the underlying mechanism. We found that subchronic CA exposure impairs reversal learning ability with dose-dependent effects but did not affect spatial learning and memory, or learning strategy. The expression and phosphorylation of N-methyl-D-aspartate receptor (NMDAR) GluN2B subunits were simultaneously reduced in the hippocampus and the GluN2B-mediated synaptic function, including long-term depression (LTD) and paired-pulse facilitation (PPF), was suppressed. CA could also diminish postsynaptic density protein-95 (PSD-95) expression but did change the levels of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor (AMPAR) GluA1 or NMDAR GluN2A subunit, or hippocampal spine density. Meanwhile, CA depressed frequency and amplitude of GluN2B-mediated EPSCs, indicating the presynaptic and postsynaptic actions of CA on neuronal activity. Furthermore, the DL-TBOA infusions could effectively mitigate the diminished GluN2B-LTD and GluN2B-EPSCs and the impairments in behavioral flexibility. Our findings provide the first evidence that CA can exert neurotoxic effects on females and certify that one of the potential mechanisms for neuronal and synaptic dysfunction is the GluN2B-mediated signaling pathway.

Melamine regulatory assessment for endocrine disruption

Melamine has several domestic and industrial uses as a flame retardant or in the manufacture of melamine-formaldehyde resins. Based on available scientific literature data, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) included this substance in the list of "chemicals that may present endocrine disruptor (ED) properties", and the substance was prioritized to assess whether it should be classified as an ED in European Union (EU) regulations for hazard identification. This review reports the assessment of melamine based on relevant studies from the registration dossier under REACH, and peer-reviewed literature. Among the various adverse effects, reproductive, neurodevelopmental, and thyroid effects were analyzed in particular, because they could be the consequence of an endocrine disruption. The different modes of action (endocrine or non-endocrine) potentially leading to these effects were scrutinized to understand whether the WHO definition for ED and the criteria for hazard identification were met. It was concluded that the reproductive effect on spermatogenesis was not a consequence of endocrine activity. A biologically plausible link between this effect and endocrine activity was not established, and other modes of action (oxidative stress or altered energy metabolism) could be involved. Similarly, thyroid and neurodevelopmental effects appeared at higher doses than those leading to renal toxicity. Our assessment confirms that melamine is a reprotoxic substance but does not support ED classification. This assessment illustrates the scientific and regulatory challenges in differentiating specific endocrine disruption from an indirect endocrine effect resulting from non-ED mediated systemic toxicity.

Nootkatone Counteracts Melamine-Mediated Nephrotoxicity via Modulation of Intermediate Filament Proteins, Oxidative, Inflammatory, and Apoptotic Events

Background

Nootkatone (NK), a bioactive sesquiterpene ketone, is a major ingredient in grapefruit that has distinguished biological activities. Melamine (MM), a food adulterant, was reported to induce toxic effects including renal disorders. Hence, this protocol was devoted to evaluate the renoprotective impact of NK toward MM-evoked renal damage.

Methods

Rats were either exposed to MM (700 mg/kg) or a combination of MM and two doses of NK (5 and 10 mg/kg).

Results

The results showed that NK therapy notably decreased the kidney functional parameters, along with KIM-1 and NGAL expressions of MM group. Furthermore, a decrease in MDA and NO levels as well as an elevation in SOD, CAT, GSH, and SOD and NRF2 mRNA expression in the NK group demonstrated NK's ability to enhance the renal antioxidant defense of the MM group. Significant suppression in renal inflammatory markers was achieved by NK via lessening of IL-1β and TNF-α, besides downregulation of NF-κB and IL-1β expressions. NK also downregulated vimentin, nestin, and desmin in the MM group. Additionally, in response to the MM exposure, NK hindered renal apoptosis by decreasing caspase-3 expression and restoring renal histopathological features.

Conclusion

These outcomes suggest that NK can be considered as a prospective candidate to guard against MM exposure-mediated renal toxic effects.

Current Insights into the Neurotoxicity of Melamine: A Comprehensive Review

Melamine, a heterocyclic nitrogen-rich triazine chemical compound, is widely used in various household products, including furniture, dinnerware, and kitchen appliances. The unauthorized addition of the mixture to various foodstuffs to misrepresent protein content resulted in catastrophic, frequently life-threatening health consequences for kids as well as canines and has garnered international attention. Numerous primary studies and evaluations have been focused on melamine toxicity's implications on kidney function. Despite the profusion of literature on melamine's nephrotoxicity, evidence regarding its toxicity to other organs remains scarce. A number of recent studies suggest melamine can disrupt central nervous system (CNS) function and bring about cognitive impairments, contradicting the commonly held belief that melamine's detrimental effects are limited to the urinary system. The accumulation of melamine in the body is linked to various adverse effects, including depression, impaired synaptic transmission, oxidative stress, and neurodegenerative diseases. Several mechanisms may lead to such complications. However, numerous safeguards against melamine accumulation have been identified. This review could shed light on the potential neurological effects and mechanisms underlying melamine toxicity. Afterward, we will dive into the body's possible protective mechanisms against melamine-induced toxicity.

Aluminum Oxide Nanoparticles Impair Working Memory and Neuronal Activity through the GSK3β/BDNF Signaling Pathway of Prefrontal Cortex in Rats

Studies demonstrated that alumina nanoparticles (alumina NPs) impair spatial cognition and hippocampus-dependent synaptic plasticity. Although alumina NPs accumulate in the prefrontal cortex (PFC), their effects on PFC-mediated neuronal and cognitive function have been not yet documented. Here, alumina NPs (10 or 20 μg/kg of body weight) were bilaterally injected into the medial PFC (mPFC) of adult rats, and the levels of glycogen synthase kinase 3β (GSK3β) and the brain-derived neurotrophic factor (BDNF) were detected. The PFC-dependent working memory task with one-minute or three-minute delay time was conducted. Meanwhile, the neuronal correlates of working memory performance were recorded. The specific expression of neuronal BDNF was assessed by colabeled BDNF expression with the neuronal nuclear antigen (NeuN). Whole-cell patch-clamp recordings were employed to detect neuronal excitability. Intra-mPFC alumina NP infusions significantly enhanced the expression of GSK3β but reduced the phosphorylation of GSK3β (pGSK3β) and BDNF levels more severely at a dose of 20 μg/kg. Alumina NPs acted in a dose-dependent manner to impair working memory. The neuronal expression of BDNF in the 20 μg/kg group was markedly declined compared with the 10 μg/kg group. During the delay time, the neuronal frequency of pyramidal cells but not interneurons was significantly weakened. Furthermore, both the frequency and amplitude of the excitatory postsynaptic currents (EPSCs) were descended in the mPFC slices. Additionally, the infusion of GSK3β inhibitor SB216763 or BDNF could effectively attenuate the impairments in neuronal correlate, neuronal activity, and working memory. From the perspective of the identified GSK3β/BDNF pathway, these findings demonstrated for the first time that alumina NPs exposure can be a risk factor for prefrontal neuronal and cognitive functions.

Co-exposure of melamine and cyanuric acid as a risk factor for oxidative stress and energy metabolism: Adverse effects on hippocampal neuronal and synaptic function induced by excessive ROS production

Melamine (MEL) and cyanuric acid (CA) alone have relatively low toxicity, but together they may cause serious damage to multiple organs, including the central nervous system, however, the underlying mechanism is unknown. This study aimed to determine and compare the neurotoxic effects of MEL (20 μg/mL), CA (20 μg/mL) and their combination (10 μg/mL MEL and 10 μg/mL CA) on cultured hippocampal neurons. The cell viability, apoptosis, anti-oxidative and energy metabolic indices were detected following 24 h of incubations. The miniature excitatory postsynaptic currents (mEPSCs), miniature inhibitory postsynaptic currents (mIPSCs) and synaptic plasticity in the hippocampal CA1 neurons were recorded. Moreover, ROS scavenger NAC was co-infused to investigate the potential mechanism. We found the complex of MEL and CA but not their alone caused severe cell death and disturbed energy production through activation caspase-3-mediated apoptosis. Meanwhile, the combination significantly reduced the amplitude, decay time and frequency of mEPSCs but not mIPSCs, indicating the pre- and post-synaptic inhibitory actions on neuronal activity. Paired-pulsed ratio (PPR) and long-term potentiation (LTP) at the Schaffer collateral-CA1 synapses were critically depressed. However, the co-application of NAC could effectively mitigate the cellular apoptosis, energy metabolism dysfunction and the impairments in neuronal and synaptic function. Our findings provide the first evidence that the combination of MEL and CA can exert more prominently neurotoxic effects than their alone and certify that one of the potential mechanisms for neuronal and synaptic dysfunction is the ROS-mediated signaling pathway.

Maternal immune activation-induced proBDNF-mediated neural information processing dysfunction at hippocampal CA3-CA1 synapses associated with memory deficits in offspring

Prenatal exposure to maternal infection increases the risk of offspring developing schizophrenia in adulthood. Current theories suggest that the consequences of MIA on mBDNF secretion may underlie the increased risk of cognitive disorder. There is little evidence for whether the expression of its precursor, proBDNF, is changed and how proBDNF-mediated signaling may involve in learning and memory. In this study, proBDNF levels were detected in the hippocampal CA1 and CA3 regions of male adult rats following MIA by prenatal polyI:C exposure. Behaviorally, learning and memory were assessed in contextual fear conditioning tasks. Local field potentials were recorded in the hippocampal CA3-CA1 pathway. The General Partial Directed Coherence approach was utilized to identify the directional alternation of neural information flow between CA3 and CA1 regions. EPSCs were recorded in CA1 pyramidal neurons to explore a possible mechanism involving the proBDNF-p75NTR signaling pathway. Results showed that the expression of proBDNF in the polyI:C-treated offspring was abnormally enhanced in both CA3 and CA1 regions. Meanwhile, the mBDNF expression was reduced in both hippocampal regions. Intra-hippocampal CA1 but not CA3 injection with anti-proBDNF antibody and p75NTR inhibitor TAT-Pep5 effectively mitigated the contextual memory deficits. Meanwhile, reductions in the phase synchronization between CA3 and CA1 and the coupling directional indexes from CA3 to CA1 were enhanced by the intra-CA1 infusions. Moreover, blocking proBDNF/p75NTR signaling could reverse the declined amplitude of EPSCs in CA1 pyramidal neurons, indicating the changes in postsynaptic information processing in the polyI:C-treated offspring. Therefore, the changes in hippocampal proBDNF activity in prenatal polyI:C exposure represent a potential mechanism involved in NIF disruption leading to contextual memory impairments.

Prenatal cyanuric acid exposure disrupts cognitive flexibility and mGluR1-mediated hippocampal long-term depression in male rats

Cyanuric acid is one of the most widely used classes of industrial chemicals and is now well known as food adulterant and contaminant in pet food and infant formula. Previously, it was reported that animals prenatally exposed to cyanuric acid showed neurotoxic effects that impaired memory consolidating and suppressed long-term potentiation (LTP) in the hippocampus. However, it is not clear if prenatal exposure to cyanuric acid induces deficits in reversal learning and long-term depression (LTD), which is required for the developmental reorganization of synaptic circuits and updating learned behaviors. Here, pregnant rats were i.p. injected with cyanuric acid (20 mg/kg) during the whole of gestation, and male offspring were selected to examine the levels of hippocampal mGluR1 and mGluR2/3 in young adulthood. The LTD at the Schaffer collateral-CA1 pathway was induced by low-frequency stimulation (LFS) and recorded. Reversal learning and hippocampus-dependent learning strategy were tested in Morris-water maze (MWM) and T-maze tasks, respectively. To further confirm the potential mechanism, selective agonists of mGluR1 and mGluR2/3 and antagonists of mGluR were intra-hippocampal infused before behavioral and neuronal recording. We found the levels of alkaline phosphatase were markedly increased in the maternal placenta and fetal brain following prenatal exposure. The expression of mGluR1 but not mGluR2/3 was significantly decreased and mGluR1-mediated LTD was selectively weakened. Prenatal cyanuric acid impaired reversal learning ability, without changing place learning strategy. The mGluR1 agonist could effectively enhance LFS-induced LTD and mitigate reversal learning deficits. Meanwhile, the reductions in the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPAR)-mediated spontaneous excitatory postsynaptic currents (sEPSCs) amplitude and frequency of cyanuric acid offspring were simultaneously alleviated by mGluR1 agonist infusions. Therefore, the results indicate the cognitive and synaptic impairments induced by prenatal cyanuric acid exposure are attributed to the disruption of the hippocampal mGluR1 signaling. Our findings provided the first evidence for the deteriorated effects of cyanuric acid on synaptic depression and advanced cognitive performance.

Aluminium oxide nanoparticles compromise spatial memory performance and proBDNF-mediated neuronal function in the hippocampus of rats

Background

Alumina nanoparticles (aluminaNPs), which are widely used in a range of daily and medical fields, have been shown to penetrate blood-brain barrier, and distribute and accumulate in different brain areas. Although oral treatment of aluminaNPs induces hippocampus-dependent learning and memory impairments, characteristic effects and exact mechanisms have not been fully elucidated. Here, male adult rats received a single bilateral infusion of aluminaNPs (10 or 20 µg/kg of body weight) into the hippocampal region, and their behavioral performance and neural function were assessed.

Results

The results indicated that the intra-hippocampus infusions at both doses of aluminaNPs did not cause spatial learning inability but memory deficit in the water maze task. This impairment was attributed to the effects of aluminaNP on memory consolidation phase through activation of proBDNF/RhoA pathway. Inhibition of the increased proBDNF by hippocampal infusions of p75^NTR antagonist could effectively rescue the memory impairment. Incubation of aluminaNPs exaggerated GluN2B-dependent LTD induction with no effects on LTD expression in hippocampal slices. AluminaNP could also depress the amplitude of NMDA-GluN2B EPSCs. Meanwhile, increased reactive oxygen specie production was reduced by blocking proBDNF-p75^NTR pathway in the hippocampal homogenates. Furthermore, the neuronal correlate of memory behavior was drastically weakened in the aluminaNP-infused groups. The dysfunction of synaptic and neuronal could be obviously mitigated by blocking proBDNF receptor p75^NTR, implying the involvement of proBDNF signaling in aluminaNP-impaired memory process.

Conclusions

Taken together, our findings provide the first evidence that the accumulation of aluminaNPs in the hippocampus exaggeratedly activates proBDNF signaling, which leads to neural and memory impairments.

Prelimbic proBDNF Facilitates Retrieval-Dependent Fear Memory Destabilization by Regulation of Synaptic and Neural Functions in Juvenile Rats

Fear regulation changes as a function of the early life is a key developmental period for the continued maturation of fear neural circuitry. The mechanisms of fear retrieval-induced reconsolidation have been investigated but remain poorly understood. The involvement of prelimbic proBDNF in fear memory extinction and its mediated signaling have been reported previously. Specifically, blocking the proBDNF/p75^NTR pathway during the postnatal stage disrupts synaptic development and neuronal activity in adulthood. Given the inherent high expression of proBDNF during the juvenile period, we tested whether the prelimbic proBDNF regulated synaptic and neuronal functions allowing to influencing retrieval-dependent memory processing. By examining the freezing behavior of auditory fear-conditioned rats, we found the high level of the prelimbic proBDNF in juvenile rats enhanced the destabilization of the retrieval-dependent weak but not strong fear memory through activating p75^NTR-GluN2B signaling. This modification of fear memory traces was attributed to the increment in the proportion of thin-type spine and promotion in synaptic function, as evidenced by the facilitation of NMDA-mediated EPSCs and GluN2B-dependent synaptic depression at the prelimbic projection. Furthermore, the strong prelimbic theta- and gamma-oscillation coupling predicted the suppressive effect of juvenile proBDNF on the recall of postretrieval memory. Our results critically emphasize the importance of developmental proBDNF for modification of retrieval-dependent memory and provide a potential critical targeting to inhibit threaten memories associated with neurodevelopment disorders.

Prenatal cyanuric acid exposure depresses hippocampal synaptic plasticity and induces spatial learning and memory deficits

The infant and fetus may be exposed to cyanuric acid (CA) via several different routes into the diet or milk product as well as deliberate contamination. Previous findings indicated chronic CA treatment caused neurotransmission and synaptic impairment in the early developing hippocampus. This study was designed to characterize the effects of different doses (10 mg/kg, 20 mg/kg and 40 mg/kg) of CA exposure on the developing fetus. Pregnant rats were intraperitoneally exposed to CA during the entire period of gestation and male offspring were selected for water maze task, neural recording and N-methyl-d-aspartate (NMDA) receptor detection around the eighth postnatal week. We found that CA exposure impaired the learning and memory function in a dose-dependent manner. The paired-pulse ratio (PPR) and GluN2A-dependent long-term potentiation (LTP) at the Schaffer collateral-CA1 pathway were affected in CA-exposed rats. Remarkably, hippocampal levels of NMDA-GluN2A, but not NMDA-GluN2B, were significantly decreased. Meanwhile, the spine density of hippocampal CA1 neurons was not altered by the CA exposure. Our findings are consistent with the hypothesis that CA treatment during the prenatal period produces deficits in spatial cognition by disrupting hippocampal synaptic function.

Melamine impairs working memory and reduces prefrontal activity associated with inhibition of AMPA receptor GluR2/3 subunit expression

Recent studies have reported that melamine can accumulate in several regions of the brain including the medial prefrontal cortex (mPFC). Although melamine accumulation in the hippocampus has been verified to induce cognitive impairments, whether it can cause mPFC-dependent working memory deficits is still unknown. After chronic treatment with melamine (150 (Mel(150)) or 300 (Mel(300)) mg/kg), rats were tested during both delay nonmatching-to-sample spatial and odor discrimination tasks. Levels of AMPA receptor subunits in the mPFC were detected using western blotting. To further explore the mechanism at the cellular level, prefrontal activity was recorded during the odor discrimination. The working memory of Mel(150) rats was found to be significantly impaired in a 3-minute delay odor discrimination task (control: n = 6, Mel(150): n = 6; P < 0.05). Compared with the control group (n = 6), rats in the 300 mg/kg Mel(300)-treated group (n = 8) displayed working memory deficits in 60-second delay Y-maze task (P < 0.05), 1-minute and 3-minute delay odor discrimination tasks (both P < 0.05). The levels of AMPA receptor mGluR2/3 subunit were significantly decreased in rats of the Mel(150) (n = 7) and Mel(300) (n = 7) groups (both P < 0.05). Exposure to 150 (n = 7) or 300 mg/kg (n = 7) melamine resulted in significant inhibition of the regular-spiking neuron activity during the delay period of the memory test (both P < 0.05). Intraperitoneal (n = 7) and intra-mPFC (n = 6) infusions of GluR2/3 agonists, effectively enhanced the neural correlate (both P < 0.05) while rescuing cognitive deficits in Mel(300)-treated rats (both P < 0.05). Collectively, these findings suggested that melamine could induce prefrontal dysfunction and cause cognitive impairments.

Requirements of Postnatal proBDNF in the Hippocampus for Spatial Memory Consolidation and Neural Function

Mature brain-derived neurotrophic factor (BDNF) and its downstream signaling pathways have been implicated in regulating postnatal development and functioning of rodent brain. However, the biological role of its precursor pro-brain-derived neurotrophic factor (proBDNF) in the postnatal brain remains unknown. The expression of hippocampal proBDNF was blocked in postnatal weeks, and multiple behavioral tests, Western blot and morphological techniques, and neural recordings were employed to investigate how proBDNF played a role in spatial cognition in adults. The peak expression and its crucial effects were found in the fourth but not in the second or eighth postnatal week. Blocking proBDNF expression disrupted spatial memory consolidation rather than learning or memory retrieval. Structurally, blocking proBDNF led to the reduction in spine density and proportion of mature spines. Although blocking proBDNF did not affect N-methyl-D-aspartate (NMDA) receptor (NMDAR) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) subunits, the learning-induced phosphorylation of the GluN2B subunit level declined significantly. Functionally, paired-pulse facilitation, post-low-frequency stimulation (LFS) transiently enhanced depression, and GluN2B-dependent short-lasting long-term depression in the Schaffer collateral-CA1 pathway were weakened. The firing rate of pyramidal neurons was significantly suppressed around the target region during the memory test. Furthermore, the activation of GluN2B-mediated signaling could effectively facilitate neural function and mitigate memory impairment. The findings were consistent with the hypothesis that postnatal proBDNF played an essential role in synaptic and cognitive functions.

Light Promotes Neural Correlates of Fear Memory via Enhancing Brain-Derived Neurotrophic Factor (BDNF) Expression in the Prelimbic Cortex

Exposure to light has been shown to enhance vigilance and improve working memory, possibly due to changes in prefrontal function. Ample evidence supports the critical role of prefrontal cortex (PFC) in fear memory performance. However, the effects of light on memory processing and its potential mechanisms remain unclear. Here, through rats exposure conditioned to light at different memory phases, we sought evidence for the influences by employing behavioral tests, pharmacological infusions, immunoblotting, and electrophysiological recording. Exposure to light immediately following conditioning of 30 min or longer could effectively improve consolidation of fear memory without altering short-term memory or upgrading the original fear. The absence of significant freezing during baseline and intertrial interval periods ruled out the possibility of a general induction of freezing by light. Meanwhile, rats exposed to light in homecages or conditioning chambers exhibited a similar memory phenotype, indicating that light specifically enhanced the fear stimulus rather than the contextual environment. Furthermore, light exposure elevated the training-induced brain-derived neurotrophic factor (BDNF) expression in the prelimbic, but not infralimbic, subregion of the PFC. Moreover, the BDNF-TrkB pathway, but not the BDNF-p75^NTR pathway, was involved in light-mediated fear memory. The enhancement in BDNF activity effectively facilitated firing correlates of prelimbic pyramidal neurons but not fast-spiking interneurons. Blocking the training-induced BDNF by its antibody abolished the effects of light on neural function and fear memory. Therefore, our findings indicate that light enhances training-induced BDNF expression that promotes the neural correlate of memory function.

Chronic Cyanuric Acid Exposure Depresses Hippocampal LTP but Does Not Disrupt Spatial Learning or Memory in the Morris Water Maze

Exposure to cyanuric acid (CA) causes multiple organ failure accompanied by the involvement in kinds of target proteins, which are detectable and play central roles in the CNS. The hippocampus has been identified as a brain area which was especially vulnerable in developmental condition associated with cognitive dysfunction. No studies have examined the effects of CA on hippocampal function after in vitro or in vivo treatment. Here, we aimed to examine hippocampal synaptic function and adverse behavioral effects using a rat model administered CA intraperitoneally or intrahippocampally. We found that infusion of CA induced a depression in the frequency but not the amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), miniature excitatory postsynaptic currents (mEPSCs), or N-methyl-D-aspartate (NMDA)-mediated excitatory postsynaptic currents (EPSCs) of the CA1 neurons in dose-dependent pattern. Both intraperitoneal and intrahippocampal injections of CA suppressed hippocampal LTP from Schaffer collaterals to CA1 regions. Paired-pulse facilitation (PPF), a presynaptic phenomenon, was enhanced while the total and phosphorylated expression of NMDA-GluN1, NMDA-GluN2A, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-GluA1 subunits were comparable between CA-treated and control groups. In Morris water maze test, both groups could effectively learn and retain spatial memory. Our studies provide the first evidence for the neurotoxic effect of CA and the insight into its potential mechanisms.

Melamine Disrupts Acetylcholine-Mediated Neural Information Flow in the Hippocampal CA3-CA1 Pathway

Considering the cognitive and synaptic deficits following intragastric administration of melamine, the aim of the current investigation was to test whether the hippocampal oscillations were affected. The local field potential (LFP) was recorded in the hippocampal CA3–CA1 pathway of Wistar rats during a spatial-dependent Y-maze task. The general partial directed coherence (gPDC) method was used to assess the directionality of neural information flow (NIF) between the CA3 and CA1 regions. The levels of acetylcholine (ACh) and its esterolytic protease, acetylcholinesterase (AChE), were detected in the hippocampus (HPC) following the behavioral test. The values of phase synchronization between the CA3 and CA1 regions in delta, low theta, and high theta oscillations were reduced significantly in the melamine-treated group. Moreover, the coupling directional index and the strength of CA3 driving CA1 were critically decreased in the above three frequency bands as well. Meanwhile, a reduction in ACh expression and an enhancement in AChE activity were found in the HPC of melamine-treated rats. Intrahippocampal infusion with ACh could mitigate the weakened neural coupling and directional NIF in parallel with spatial learning improvements. However, infusion of scopolamine, an acetylcholine receptor antagonist, could block the mitigative effects of ACh treatment in melamine rats. These findings provide first evidence that ACh-mediated neuronal coupling and NIF in the CA3–CA1 pathway are involved in spatial learning deficits induced by chronic melamine exposure.

Melamine disrupts spatial reversal learning and learning strategy via inhibiting hippocampal BDNF-mediated neural activity

Although several studies showed adverse neurotoxic effects of melamine on hippocampus (HPC)-dependent learning and reversal learning, the evidence for this mechanism is still unknown. We recently demonstrated that intra-hippocampal melamine injection affected the induction of long-term depression, which is associated with novelty acquisition and memory consolidation. Here, we infused melamine into the HPC of rats, and employed behavioral tests, immunoblotting, immunocytochemistry and electrophysiological methods to sought evidence for its effects on cognitive flexibility. Rats with intra-hippocampal infusion of melamine displayed dose-dependent increase in trials to the criterion in reversal learning, with no locomotion or motivation defect. Compared with controls, melamine-treated rats avoided HPC-dependent place strategy. Meanwhile, the learning-induced BDNF level in the HPC neurons was significantly reduced. Importantly, bilateral intra-hippocampal BDNF infusion could effectively mitigate the suppressive effects of melamine on neural correlate with reversal performance, and rescue the strategy bias and reversal learning deficits. Our findings provide first evidence for the effect of melamine on cognitive flexibility and suggest that the reversal learning deficit is due to the inability to use place strategy. Furthermore, the suppressive effects of melamine on BDNF-mediated neural activity could be the mechanism, thus advancing the understanding of compulsive behavior in melamine-induced and other neuropsychiatric disorders.

Subacute melamine exposure disrupts task-based hippocampal information flow via inhibiting the subunits 2 and 3 of AMPA glutamate receptors expression

Although melamine exposure induces cognitive deficits and dysfunctional neurotransmission in hippocampal Cornus Ammonis (CA) 1 region of rats, it is unclear whether the neural function, such as neural oscillations between hippocampal CA3-CA1 pathway and postsynaptic receptors involves in these effects. The levels of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) subunit glutamate receptor (GluR) 1 and GluR2/3 in CA1 region of melamine-treated rats, which were intragastric treated with 300 mg/kg/day for 4 weeks, were detected. Following systemic or intra-hippocampal CA1 injection with GluR2/3 agonist, spatial learning of melamine-treated rats was assessed in Morris water maze (MWM) task. Local field potentials were recorded in CA3-CA1 pathway before and during behavioral test. General Partial Directed Coherence approach was applied to determine directionality of neural information flow between CA3 and CA1 regions. Results showed that melamine exposure reduced GluR2/3 but not GluR1 level and systemic or intra-hippocampal CA1 injection with GluR2/3 agonist effectively mitigated the learning deficits. Phase synchronization between CA3 and CA1 regions were significantly diminished in delta, theta and alpha oscillations. Coupling directional index and strength of CA3 driving CA1 were marked reduced as well. Intra-hippocampal CA1 infusion with GluR2/3 agonist significantly enhanced the phase locked value and reversed the melamine-induced reduction in the neural information flow (NIF) from CA3 to CA1 region. These findings support that melamine exposure decrease the expression of GluR2/3 subunit involved in weakening directionality index of NIF, and thereby induced spatial learning deficits.

Prevention of melamine-induced hepatorenal impairment by an ethanolic extract of Moringa oleifera: Changes in KIM-1, TIMP-1, oxidative stress, apoptosis, and inflammation-related genes

BACKGROUND/AIMS

Melamine (ML) is a common food adulterant and contaminant. Moringa oleifera is a well-known medicinal plant with many beneficial biological properties. This study investigated the possible prophylactic and therapeutic activity of an ethanolic extract of M. oleifera (MEE) against ML-induced hepatorenal damage.

METHOD

Fifty male Sprague Dawley rats were orally administered distilled water, MEE (800 mg/kg bw), ML (700 mg/kg bw), MEE/ML (prophylactically) or MEE+ML (therapeutically). Hepatic aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphate (ALP) in serum were measured. Serum total bilirubin, direct bilirubin, indirect bilirubin, protein, albumin, and globulin contents were also assayed, and urea and creatinine levels were determined. Moreover, antioxidant enzyme activity of glutathione peroxidase (GPx) and catalase (CAT) in serum levels were quantified. Complementary histological and histochemical evaluation of renal and hepatic tissues was conducted, and expression of oxidative stress (GPx and CAT) and apoptosis-related genes, p53 and Bcl-2, in hepatic tissue were assessed. In parallel, transcriptional expression of inflammation and renal injury-related genes, including kidney injury molecule 1 (KIM-1), metallopeptidase inhibitor 1 (TIMP1), and tumor necrosis factor alpha (TNF-α) in the kidney tissue were determined.

RESULTS

ML caused significant increases in serum levels of ALT, AST, ALP, total bilirubin, direct bilirubin, indirect bilirubin, urea, and creatinine. Further, ML treated rats showed significant reductions in serum levels of protein, albumin, globulin, GPx, and CAT. Distinct histopathological damage and disturbances in glycogen and DNA content in hepatic and renal tissues of ML treated rats were observed. KIM-1, TIMP-1, and TNF-α gene expression was significantly upregulated in kidney tissue. Also, GPx, CAT, and Bcl-2 genes were significantly downregulated, and p53 was significantly upregulated in liver tissue after ML treatment. MEE significantly counteracted the ML-induced hepatorenal damage primarily for co-exposed rats.

CONCLUSION

MEE could be an effective therapeutic supplement for treatment of ML-induced hepato-renal damage, probably via modulating oxidative stress, apoptosis, and inflammation.