Effect Of B"a"P Exposure On Long-term Potentiation In Rat Hippocampal CAl Area

Benz[a]pyrene (B[a]P),a product of incomplete combustion at high temperature ,widely existed in environment ,one of polycyclic aromatic hydrocarbon(PAH) compounds .The carcnogencity of B[a]P is well established in human and animal model. B[a]P usually be harmful as a research study on behalf of polycyclic aromatic hydrocarbons.. The researchers have shown that B[a]P could damage nerve tissue by neurology experiment. When rats exposed to B[a]P their short-term memory and spatial memory decline. The role of B[a]P and B [a] P metabolites in plasma and brain were significantly related. Hippocampus is the key to learning and memory brain .Hippocampal long–term potentiation (LTP),a persistent enhancement of excitatory synaptic transmission induced by high-frequency stimulation(HFS),has been accepted for the cellular basis of learning and memory .At present the synaptic mechanism of neurotoxicity of B[a]P has not been fully elucidated. Therefore, explore the effect of B[a]P exposure on LTP and the biochemical indexes related to synaptic mechanisms, this will help to clarify the mechanisms of B[a]P exposure on brain damage in learning and memory .Objective:(1)To observe the effects of B[a]P on the induction and maintenance of long-term potentiation in rat hippocampus in vivo;(2)To observe the effects of B[a]P exposure at different dose on the expression and phosphorylation of Calmodulin-Dependent Protein KinaseⅡ,protein kinase c and cAMP-dependent protein kinase A;(3) To observe the effects of B[a]P exposure at different dose on the mRNA expression of Calmodulin-Dependent Protein KinaseⅡ,protein kinase c and cAMP-dependent protein kinase A;(4) Further explore the B[a]P effects on learning and memory and its synaptic mechanisms.Methods:(1)Group and exposure :According to the results of behavioral tests ,healthy adult SD rats (100g)were divided into 5 groups ,including a control group ,a solvent control group and three B[a]P–treated groups ,which were administered intra-peritoncally with three doses from 1.0,2.5,to 6.25mg/kg body weight (BW) for 90days.(2)Electrophysiological recordings :The extracellular micropipette recording technique was used to recording electrophysiological change.(3)Expression of protein : After electrophysiological recording ,dislodge the hippocampus .According to Western blot measured the expression and phosphorylation of CaMKⅡ,PKC,PKA in hippocampus .(4) Expression of mRNA in hippocampus : After electrophysiological recording ,dislodge the hippocampus . According to Q-PCR measured the mRNA expression of CaMKⅡ,PKC,PKA in hippocampus .(5)Statistical analysis .Results:The results demonstrated the inhibition of B[a]P to LTP induced by HFS in rats hippocampus CA1 area in a dose–dependent manner, with the average amplitude of fEPSPs 7.5%( P<0.05), 16.8%(P<0.01) and 28.2%(P<0.01) decreasing respectively in 1.0, 2.5 and 6.25 mg/kg B[a]P groups compared to olive oil control group(no significantly with physiological saline control group ).LTP are inhibited with the levels of CaMKⅡ, PKC, PKA proteins 15.2%(P<0.05),1.5%(P>0.05) and 5.0% (P>0.05) decreasing in 1.0 mg/kg B[a]P group ,23.2%(P<0.05),29.3%( P<0.05) and 15.4% (P<0.05) decreasing in 2.5mg/kg B[a]P group , 49.5%(P<0.05),56.9%( P<0.05) and 31.7% (P<0.05) decreasing in 6.25mg/kg B[a]P group compared to olive oil control group(no significantly with physiological saline control group ).LTP are inhibited with the phosphorylation of CaMKⅡ, PKC, PKA proteins 2.6%(P>0.05),23.4%(P>0.05) and 4.1% (P>0.05) decreasing in 1.0 mg/kg B[a]P group , 25.0%(P<0.05),29.9%( P<0.05) and 30.1% (P<0.05) decreasing in 2.5mg/kg B[a]P group , 43.4%(P<0.01),51.4%( P<0.01) and 45.2% (P<0.01) decreasing in 6.25mg/kg B[a]P group compared to olive oil control group(no significantly with physiological saline control group ).LTP are inhibited with the mRNA levels of CaMKⅡ,PKC,PKA 0.0%(P>0.05),12.5%(P<0.05) and 3.3% (P>0.05) decreasing in 1.0 mg/kg B[a]P group , 5.6%(P<0.05),15.0%( P<0.05) and 6.7% (P<0.05) decreasing in 2.5mg/kg B[a]P group , 19.2%(P<0.01),30.0%( P<0.01) and 15.8% (P<0.01) decreasing in 6.25mg/kg B[a]P group compared to olive oil control group(no significantly with physiological saline control group ).There are positive correlations between average amplitude of fEPSPs and expression of CaMKⅡ,PKC,PKA in hippocampus(r=0.800,0.563,0.704,P<0.001), phosphorylation of CaMKⅡ,PKC,PKA in hippocampus(r=0.736,0.713,0.819,P<0.001), mRNA levels of CaMKⅡ,PKC,PKA (r=0.669,0.853,0.501,P<0.001).Conclusion:Sub-chronic B[a]P exposure impaired the induction and maintenance of LTP in rats in a dose–dependent manner. Sub-chronic B[a]P exposure reduced the expression and phosphorylation of CaMKⅡ,PKC,PKA in hippocampus and reduced the expression of mRNA of CaMKⅡ,PKC,PKA in hippocampus . Provide preliminary theoretical basis for from molecular level elucidate Sub-chronic B[a]P exposure can damage the function of learning and memory .