The Effect And Mechanism Of Noise Exposure On The Capability Of Learning And Memory In Immature Rat

Objective:To observe the effect of noise exposure on the capability of learning and memory and the neurotransmitter of hippocampus in immature rat, And to probe the possible mechanism of noise exposure on the capability of learning and memory in immature rat.Methods:52 Wistar immature rats were divided randomly into two groups,noise group and control group.The immature rats in the noise group were exposed to 80dB(A)noise constantly for one month.The capability of learning and memory of immature rats was measured by device of Morris water maze and shuttle box.The morphology of neuron in the hippocampus of immature rats was observed by haematine-eosin.The ultrastructure of neuron in the hippocampus of immature rats was observed by the transmission electron microscopy.An immunohistochemical method was used to observe the expression of glutamic acid(Glu),r-aminobutyric acid (GABA)and nitricoxide synthase(NOs)positive neurons in the hippocampus of immature rats.The activity of choline acetyltransferase(ChAT)and acetylcholineeesterase(AChE)in the hippocampus of immature rats was detected by chemical colorimetry.The acetylcholine(ACh)content in the hippocampus of immature rats was detected by alk hydroxylamine colorimetry.The monoamine transmitter content in the hippocampus of immature rats was detected by high performance liquid chromatography- electrochem method.Results:In the Morris water maze test,the average escape latency of immature rats in the noise group was longer than that in the control group(P<0.05)and the frequency to bestride platform of immature rats in the noise group were less(P<0.01).In the shuttle box test,the active avoidance response frequency of immature rats in the noise group were less than that in the control group(P<0.01)and the active avoidance response latency and the passive avoidance response latency of immature rats in the noise group were longer(P<0.01).The non apparent abnormality of organism in hippocampus of immature rats in the noise group was observed by haematine-eosin.The non apparent abnormality of neuron ultrastructure in hippocampus of immature rats in the noise group was observed by the transmission electron microscopy.The number and the magnitude of tinction of Glu,NOs and GABA positive neuron in hippocampus of immature rats in the noise group were less than that in the control group(P<0.01).The AChE activity in hippocampus of immature rats in the noise group enhanced obviously compared with the control group(P<0.01).The ChAT activity and ACh content in hippocampus of immature rats in the noise group decreased obviously compared with the control group(P<0.01).The DA,NE and 5-HT content in hippocampus of immature rats in the noise group decreased obviously compared with the control group(P<0.01).Conclusion:The noise does impair the capabilities of learning and memory of immature rats.The impairment may be related with the reduction of neurotransmitter content in hippocampus,which could impair the induction and maintenance of the long term potentiation and sensitization in hippocampus synapse.