The Expression Of ChAT And GDNF And Their Relationship In Diabetic Rats Brain

Objectives:Central nervous system complications of diabetes mellitus is mainly manifesified by mild or moderate disability of learning and cognition ability. Diabetes Mellitus can affect central nervous system through many ways, but the mechanisms is not definite yet now. Some think that the deline of the learning and cognition ability is relative with the decline of cholinergic function. Neurotrophic factor is important to the origination and progression of the degeneration of central nervous system. Glial cell line-derived neurotrophic factor (GDNF) has nutrition to the cholinergic neurons and has antiapotosis action,but there is few report about GDNF and central neurous system complications of diabetes mellitus.Our study aimes to use diabetic rats to discuss the mRNA and protein expression of GDNF and the expression of ChAT mRNA in brain under different blood glucose levels in diabetes, and further to evaluate the correlation between GDNF and ChAT in diabetic brain. We also will observe the change of the count and the morphology of the hippocampal CA region and brain cortex neurons to evaluate the dynamic effect of hyperglycation on the expression of GDNF and ChAT in brain. And further to reveal the possible relation between GDNF and ChAT, namely the function of GDNF in the central nervous system complications of diabetes mellitus. Materials and Methods:A total of 50 healthy male wistar rats weighting 180-220g were used, 10 ratswere randomly chosen to be normal control group (group NC), the rest 40 rats were induced to be diabetes mellitus by STZ which was injected into the abdomens and only 20 rats became diabetes finally. After the diabetic model was successfully established, the 20 rats were randomly divided into 2 groups: diabetic group without blood glucose control (group DM1), diabetic rats treated with 2 insulin (group DM2), 2 each group had 10 rats. The three DM groups were treated with protamine zinc insulin(PZI))to control their blood glucose levels to>16.7 mmol/L and <14 mmol/L, respectively. After three months the HbAjc of four groups were measured, then all rats were decapitated and their whole brains were dissected. The reverse transcription-polymerase chain reaction (RT-PCR) and immunhistochemistry methods were used to measure the mRNA expression of ChAT and the protein and the mRNA expression of GDNF, respectively. Data were analysed using the Statistical Package of the SPSS 10.0. Discriptive data were given as means±SZ>. Continuous variables were tested by analysis of t-test and the relations between the variables were tested by linear correlation. The p-values are two-tailed and a p-value of less than 0.05 being considered to be significant. Results:1. During the experiment the weights of DM1 groups were lower than the control group, but the blood glucose and HbAic were much higher than the control group. The rate of the weight growth of DM2 group was more rapid than DM1 group, and the control of blood glucose was better.2. Compared with NC group, the GDNF mRNA expression in DM1 group reduced 34.22%, in DM2 group reduced 18.80%. The differences were significant(P<0.001).3. Compared with NC group, the ChAT mRNA expression in DM1 group reduced 45.37%, in DM2 group reduced 29.26%. The differences were significant(P O.001).4. Immunohistochemistry method showed that the positive stained granules of GDNF protein in the hippocampal CA region and brain cortex were abundant in NC group. In DM1 and DM2 group the positive stained granules of GDNF proteinreduced markedly, especially in DM1 group. The difference between DM2 and NC group was also significant(P <0.01).5. Compared with NC group, the count of the hippocampal CA region neurons in DM1 group reduced 7.36%, in DM2 group did not reduce. The difference were not significant^ >0.05). Compared with NC group, the morphology of the frontal lobe cortex and hippocampal CA region neurons in DM1 group presented obvious degeneration changes, while the degree of degeneration in DM2 group reduced definitely. Conclusions:1. Chronic hyperglycemia could induce the "downregulation" of the GDNF and ChAT mRNA expression in the rat brain.2. Chronic hyperglycemia could induce the "downregulation" of the GDNF protein expression in the rat brain.3. Chronic hyperglycemia could induce the degraduation changes of the frontal lobe cortex and hippocampal CA region neurons, and even the "downregulation" of the number of neurons.4. After we controlled the blood glucose level using insulin, the expressions of GDNF mRNA and protein and the expressions of ChAT mRNA increased, and there was negative correlation between GDNF expression and HbAic level. The degeneration of the hippocampal CA region and brain cortex neurons also improved obviously.5.The GDNF mRNA expression has positive correlation with the ChAT mRNA expression(r=0.675)(P <0.05); we can deduce it is probable that GDNF has positive effect on the expression of ChAT mRNA in diabetic brain and modulate the cholinergic function. The "downregulation" of the GDNF expression caused by longterm chronic hyperglycation in the rat brain is probably relative with the decline of learning and cognition ability.