糖尿病小鼠早期视觉功能损伤与初级视觉皮层神经元功能异常的相关性分析

Correlation analysis between early visual function impairment and neuron function abnormality in diabetic mouseprimary visual cortex

目的探讨糖尿病小鼠早期视觉功能损伤及其初级视觉皮层神经元的反应特性。方法将20只SPF级7周龄雄性C57BL/6J小鼠应用随机数字表法随机分为糖尿病组和正常对照组,每组10只。糖尿病组小鼠经腹腔内注射链脲佐菌素诱导建立糖尿病模型。造模前及造模后1、2、3周检测小鼠的空腹血糖水平和体质量,并于造模后4周进行腹腔葡萄糖耐量试验以评估糖尿病模型建立情况。造模后4周,采用视网膜电图(ERG)分别记录小鼠暗适应下光刺激强度分别为0.01、3.0 cd·s/m 2的ERG反应,并于明适应10 min后记录光强度为3.0 cd·s/m 2的ERG反应评估小鼠视网膜功能;采用超广角激光扫描检眼镜检测小鼠的眼底表现;采用视觉水迷宫检测小鼠光栅辨别截止频率以评估小鼠的视觉功能;采用在体电生理技术检测小鼠初级视觉皮层(V1)神经元的空间频率调谐曲线并统计神经元的最大发放强度、自发放强度、最优空间频率、截止频率、带宽等以评估小鼠的神经元功能。结果糖尿病组10只小鼠均造模成功。造模后4周,糖尿病组小鼠暗适应光强度为0.01 cd·s/m 2的b波振幅、光强度为3.0 cd·s/m 2的a波和b波振幅以及明适应10 min后光强度为3.0 cd·s/m 2的b波振幅较正常对照组均有下降趋势,但差异均无统计学意义(均P>0.05)。眼底超广角成像检查显示糖尿病组小鼠视网膜未见明显血管改变;视觉水迷宫检测小鼠光栅辨别能力结果显示,糖尿病组小鼠截止频率为(0.45±0.06)c/d,明显低于正常对照组的(0.58±0.05)c/d,差异有统计学意义(t=5.10,P<0.05);在体电生理检查结果显示,糖尿病组小鼠视觉皮层V1区的神经元最大发放强度为4.29(2.60,8.33)spikes/s,明显低于正常对照组的7.10(4.34,11.6)spikes/s,最优空间频率、截止空间频率、带宽分别为0.03(0.02,0.05)、0.07(0.05,0.12)和0.14(0.07,0.22)c/d,明显低于正常对照组的0.41(0.03,0.05)、0.10(0.07,0.14)和0.14(0.10,0.26)c/d,差异均有统计学意义(Z=-4.29、-3.22、-3.19、-2.19,均P<0.05)。结论在糖尿病早期视网膜血管病变尚未出现时视觉功能即可出现异常,这种功能异常与视觉皮层V1区的神经元功能损伤有关。

Objective To investigate the damage of visual function in the early stage of diabetes mellitus and the response characteristics of primary visual cortex neurons in diabetic mice.Methods Twenty 7-week-old SPF grade male C57BL/6J mice were randomly divided into diabetes group and normal control group by the random number table method,with 10 mice in each group.The diabetes model in diabetes group was established by the intraperitoneal injection of streptozotocin.Fasting blood glucose concentration and body mass of mice were measured before and 1,2 and 3 weeks after modeling,and intraperitoneal glucose tolerance test was performed 4 weeks after modeling to evaluate the establishment of diabetes model.At 4 weeks after modeling,the electroretinogram(ERG)responses of mice were recorded at dark adaptation luminances of 0.01 and 3.0 cd·s/m 2,and the ERG response to light adaptation luminance of 3.0 cd·s/m 2 was recorded 10 minutes after light adaptation to evaluate the retinal function of mice.The fundus of mice was examined with an ultra-wide field laser scanning ophthalmoscope.The visual function of mice was evaluated via the cutoff frequency of grating discrimination detected by visual water maze.The spatial frequency tuning curves of primary visual cortex(V1)neurons were detected by in vivo electrophysiology technique and the maximum firing intensity,self-firing intensity,optimal spatial frequency,cutoff frequency and bandwidth of neurons were calculated to evaluate the neuronal function of mice.The research scheme was approved by the Experimental Animal Ethics Committee of Anhui Medical University(No.LLSC20230419).Results The diabetic model was successfully established in 10 mice in the diabetes group.At 4 weeks after modeling,compared with the normal control group,the b-wave amplitudes of mice at a dark adaptation luminance of 0.01 cd·s/m 2,the a-and b-wave amplitudes of mice at a dark adaptation luminance of 3.0 cd·s/m 2 and the b-wave amplitudes of mice at a light adaptation luminance of 3.0 cd·s/m 2 after 10 minutes of light adaptation showed a downward trend in diabetes group,but the differences were not statistically significant(all at P>0.05).Ultra-wide field laser scanning ophthalmoscopy showed no obvious vascular changes in the retina of diabetic mice.The results of visual water maze detection showed that the cutoff frequency of diabetes group was(0.45±0.06)c/d,which was significantly lower than(0.58±0.05)c/d of normal control group(t=5.10,P<0.05).In vivo electrophysiological results showed that the maximum firing intensity of neurons in V1 region in diabetes group 4.29(2.60,8.33)spikes/second,which was significantly lower than 7.10(4.34,11.6)spikes/second in normal control group(Z=-4.29,P<0.05).The optimal spatial frequency,cutoff spatial frequency and bandwidth were 0.03(0.02,0.05),0.07(0.05,0.12)and 0.14(0.07,0.22)c/d in diabetes group,which were significantly lower than 0.41(0.03,0.05)and 0.10(0.07,0.14),0.14(0.10,0.26)c/d of normal control group,and the differences were statistically significant(Z=-3.22,-3.19,-2.19;all at P<0.05).Conclusions The abnormal visual function may occur in the early stage of diabetes before the appearance of retinal vasculopathy,which is related to the damage of neurons in the V1 region.