Effect And Mechanisms Of Formaldehyde On Learning And Memory In Rats

Formaldehyde is a toxic substance. Studies have shown that it can be harmful obviously for the nervous system of rats, and it also has been found its neurotoxicity for the people. So the research that the effects of formaldehyde on learning and memory is very essential.Hippocampus is one of the most important structures in the limbic system of brain, and is an important part of advanced nervous activity including of learning and memory. CaMKII and Ng are the specific proteins of nervous system, especially in the post-synaptic density (PSD) of hippocampus and pallium, it has a higher expression. CaMKII is a downstream molecule of Ca2+-CaM pathway, during the study, induced phosphorylation by Ca2+influx and then is activated, activated kinase molecules catalyze autophosphorylation again, and thereby kinase molecules can maintain activated state after learning. Experiments show that CaMKII is the molecular basis of spatial learning and memory, many research report that Ng is an important protein involved in the regulation of learning and memory, which participates the signal transduction played central role during learning and memory, and it is the main regulatory aspect of synaptic plasticity. Studies have further confirmed Ng as an upstream regulatory element on the formation mechanism of memory, which plays a key role in the PKC-mediated signal transduction pathway by regulating free Ca2+and CaM. ObjectiveIn this study,exposing the rats to toxin by intraperitoneal injection, we research the effects of formaldehyde on learning and memory of rats, Ng and CaMKII expression level in brain tissue of rats, which is helpful to further reveal the mechanism of formaldehyde damaging learning and memory, and provide a theoretical scientific basis for the research of preventing the neurotoxicity of formaldehyde. MethodsWe choosed healthy (SPF grade) male rats as subjects; they were randomly divided into4groups, a normal control group given the rats normal saline by intraperitoneal injection every morning, the others groups given the rats formaldehyde solution by intraperitoneal injection every morning, dose respectively5mg/kg,10mg/kg,20mg/kg, the time of exposure separately were7days and14days. After evaluating the learning and memory of rats by the Morris water maze, we anesthetized rats by use of10%chloral hydrate, then separated the serum and brain tissue, the serum and a part of tissue were used to determined the formaldehyde concentration by the method of pre-column derivatization HPLC. Other part of tissue were used for Immunohistochemistry and Western Blotting, and observed the changes of CaMKII, Ng protein expression in hippocampus and prefrontal cortex. ResultsHPLC:The formaldehyde concentration of serum between the middle-dose group, high-dose group are higher than normal control group and low-dose group (P<0.05). The formaldehyde concentration of brain are same as that of serum.In the spatial probe test, middle-dose and high-dose groups swimming time and the percentage of swimming path in the first quadrant compared with the normal and low-dose group’s, the difference has statistically significance(P<0.05) in7days of intraperitoneal injection. In that of14days the three groups of intraperitoneal injection are longer than the normal control group on swimming time and the percentage of swimming path in the first quadrant, the swimming speed of the normal control group compared with other groups, there are statistically significance(P<0.05)On the high-dose group the expression of Ng and CaMKII in hippocampus and prefrontal cortex were significantly lowest on IHC. The expressions of Ng and CaMKII protein in hippocampus of high-dose groups were significantly lower than that of control, low-dose and middle-dose groups but there was no significant difference on WB. Conclusion1. To set up the model of injurying on spatial learning and memory by formaldehyde, there are some damage about the ability of rats’ spatial learning and memory, the ability of rats’ spatial memory were more serious2. After intraperitoneal injection formaldehyde, the expression of Ng and CaMKⅡ in hippocampus and forehead of cortex are inhibited. 3. After intraperitoneal injection formaldehyde, formaldehyde exists different level of accumulation in blood and brain tissue of rats, the extent of accumulation has a dose-response relationship.