Protection Of Hydrogen Sulfide Against Formaldehyde-induced Impairment In The Learning And Memory And The Function Of Cognition In Rats And The Underlying Mechanisms

【Background and Objective】It’s been demonstrated that excessive accumulation offormaldehyde (FA) in the body would be poisonous to human’s centralnervous system (CNS), generate oxidative-stress and result in learning andmemory and cognitive impairment. Hydrogen sulfide (H2S), a newneuromodulator, has the antioxidative and neuroprotective role andregulates synaptic plasticity. Therefore, we propose that H2S protectsagainst formaldehyde-induced impairment in learning and memory andcognition.Brain derived neurotrophic factor (BDNF), a small molecular proteinsynthesized in brains, plays an important role in neuronal survival,differentiation, synaptic plasticity, and regulation of learning and memory.Thus, we will study whether the mechanism underlying the protection ofH2S against formaldehyde-induced impairment in learning and memoryand cognition is involved in BDNF.Therefore, in the study, FA was intracerebroventricularly injected intorats to investigate the role of FA in the learning and memory and thecognitive function and study the protective effect of H2S on FA-inducedimpairment in the learning and memory and the function of cognitionand the underling mechanism. 【Methods】Learning and memory of rats was evaluated by the Morris watermaze (MWM). Cognitive function of rats was assessed by novel objectrecognition test. HE staining was applicated to analyze arrangement andquantity of neurons in CA1area of hippocampus. Neuronal apoptosis inhippocampus was observed by Tunel staining. Superoxide dismutase(SOD) and malondialdehyde (MDA) levels in the brains of rats wereaccounted by Elisa. Expression of CBS in brains was measured by Westernblot and H2S generation in brains was detected by spectrophotometer.Expression of BDNF in brains was monitored by BDNF Western blot andimmunohistochemistry.【Results】1. Formaldehyde impairs the learning and memory and the function ofcognition in rats and the underlying mechanismsAfter the rats were treated with2.5μL of FA (0.1,1,10μM) byunilateral lateral ventricle micro-injection for7d, we detected thefunction of learning and memory in rats with Morris water maze (MWM),and the cognitive function with novel object test. The results in MWMshowed that FA (10μM) extended remarkably the latency period of rats innavigation training in the5th day. In spatial research training, theproportionality of swimming time and the times of across plat of rats weremarkedly decreased by treated with FA (1,10μM). Result from novelobject test showed that the discrimination index of rats was sharplydeclined by FA (1,10μM). These data indicated that FA impairs thelearning and memory and the function of cognition.Results from HE staining showed that the neurons in CA1area inhippocampus of rats treated with FA (10μM) arranged disorderly anddecreased sharply and the data in Tunel staining demonstrated that massive apoptic neuron appeared in CA1area in hippocampus of ratstreated with FA (10μM), indicating that FA-induced impairment in thelearning and memory and the function of cognition may be associatedwith FA-caused damage and apoptosis in neurons.Treatment with FA (10μM) evidently reduced the level of SOD andincreased the content of MDA in brains of rats, implying that FA-induceddecrease in antioxidant capacity of brain is involved in its toxic effect onneurons, resulting in impairment in the learning and memory and thefunction of cognition.Treatment with FA (10μM) significantly reduced the proteinexpression of cystathionine β-synthase (CBS), a key enzyme in generationof H2S in brain, and the generation of H2S in hippocampus of rats. Thesedata indicated that FA inhibits CBS expression and H2S generation andleads to decrease in antioxidant capacity of the brain, resulting inneurotoxicity, which in turn impairs learning and memory and thecognitive action.Western blotting results showed that the expression of BDNF protein inhippocampus of rats treated with FA (10μM) was markedly decreased.The number of BDNF immunoreactive neurons of CA1area inhippocampus of rats treated with FA (10μM) declined significantly. Ourdata indicated that FA-induced impairment in the learning and memoryand the function of cognition is implicated in the BDNF protein expressionin hippocampus.2. Hydrogen sulfide antagonizes formaldehyde-induced impairment inthe learning and memory and the function of cognition in rats and theunderlying mechanismsAfter pretreatment with NaHS (1.68,3.36,6.72mg/kg, ip) for6h, therats were treated with2.5μL of FA (10μM, icv) for7d. The results from morris water maze showed that NaHS (1.68,3.36,6.72mg/kg) restored the delay of latency period in navigation training andthe reduction of proportionality reduction of swimming time in mid-ring inspace search training induced by FA (10μM). Result from novel objecttest showed that FA (10μM)-declined the discrimination index of rats wasrestored by pretreated with NaHS (1.68,3.36,6.72mg/kg). These datademonstrated that H2S ameliorated FA-exerted impairment in thelearning and memory and the function of cognition of rats.HE staining showed that NaHS (1.68,3.36,6.72mg/kg) improved thedisorder and loss of neurons in CA1area in hippocampus of rats treatedwith FA (10μM) and Tunel staining showed that NaHS (1.68,3.36,6.72mg/kg) markedly reduced the number of apoptotic neurons inhippocampus induced by FA (10μM). These results indicated that H2Sresists the damage and apoptosis of neurons induced by FA andsuggested that the protective role of H2S in the learning and memory andthe function of cognition is involved in its protection against FA-inducedneurotoxicity.Pretreatment with NaHS (1.68,3.36,6.72mg/kg) rescued thereduction of SOD and the increase in MDA induced by FA, atconcentration of10μM. These data indicated that H2S reversesFA–suppressed antioxidant capacity of brain and implied thatH2S-exerted amelioration in the antioxidant capacity of brain leads todecrease in FA-induced neurotoxicity, resulting in prevention ofFA-induced impairment in the learning and memory and the function ofcognition.Pretreatment with NaHS (1.68,3.36,6.72mg/kg) restored thesuppression in CBS protein expression and H2S generation in brain by FA(10μM). These findings indicated that H2S prevents FA-induced inhibition of CBS expression and decrease in H2S generation, which enhances theantioxidant capacity of brain and attenuates the eurotoxicity of FA, andfinally alleviates FA-impaired the learning and memory and the functionof cognition of rats.Western blotting results showed that pretreatment with NaHS (1.68,3.36,6.72mg/kg) restored the downregulation of BDNF protein expressionin hippocampus induced by FA (10μM). FA-declined BDNFimmunoreactive neurons in CA1area in hippocampus of rats was greatlyrestored by pretreatment with NaHS (1.68,3.36,6.72mg/kg). These dataindicated that H2S ameliorates FA-impaired the learning and memory andthe function of cognition through promoting the expression of BDNFprotein.【Conclusion】1. Formaldehyde-caused impairment in the learning and memory andthe function of cognition is involved in the inhibition of CBS expression andH2S generation in hippocampus, the decrease in antioxidant capacity ofbrain, the damage of neuron in hippocampus, and the downregulationof BDNF protein expression in hippocampus.2. Hydrogen sulfide prevents FA-induced impairment in the learning andmemory and the function of cognition through promoting CBS expressionand H2S generation in hippocampus, restoring the antioxidant capacity ofbrain, restraining the damage of neuron in hippocampus, and promotingthe expression of BDNF protein in hippocampus.