摘要
研究大鼠视觉发育可塑性关键期内视皮层LTP与大鼠生理年龄及视觉经验的关系 ,探讨视觉经验依赖性可塑性的突触机制和细胞机制。用低频刺激视皮层脑片Ⅳ层伴随突触后神经元去极化至 - 2 0mV ,以诱发视皮层Ⅱ～Ⅳ层LTP ,用膜片钳全细胞记录法记录 ,并观察NMDA受体拮抗剂APV对LTP的影响。结果表明 :①视皮层LTP诱发率在生后 1周龄组最低 (3/ 14 ) ,2周龄组略微增加 (9/ 2 9) ,3周龄组最高 (11/ 19) ,4周龄组次之 (7/14 )。睁眼前后LTP诱发率差异显著 (P <0 .0 5 )。②APV处理组LTP诱发率 (4/ 33)显著低于非APV处理组(2 4 / 5 4) (P <0 .0 1)。但有 4例来自Ⅳ层水平联系的突触 ,APV不能阻断LTP诱发。结果提示 :①视皮层LTP反映了生理状态下视皮层经验依赖性可塑性。睁眼前视皮层大多数突触的可塑性处于潜伏状态 ,而睁眼后形觉刺激激发了视皮层突触的可塑性。②大鼠视觉发育可塑性关键期内低频刺激视皮层Ⅳ层伴随突触后去极化所诱发的LTP是NMDA受体依赖性的。但视皮层Ⅳ层水平联系突触中存在不被 10 0 μmol/LAPV阻断的LTP。
We studied the property of LTP in layer Ⅱ～Ⅳ of rat's visual cortex at different postnatal days induced by pairing low frequency stimulation at layer Ⅳ with post synaptic depolarization in order to explore the synaptic and cellular mechanism of experience dependent plasticity in the visual cortex. The visual cortex slices were prepared from 52 Wistar rats of both genders, which were divided into four groups according to postnatal days: ① 1 week group(≤7 d), n =13;② 2 weeks group (8～14 d), n =14;③ 3 weeks group(15～21 d), n =15;④ 4 weeks group (22～28 d), n =10. Blind patch clamp whole cell recording was adopted. Pre synaptic test stimulation was given at 0.07 Hz intervals through bipolar stimulating electrodes placed in layer Ⅳ. EPSCs of layer Ⅱ～Ⅳ were recorded by recording electrodes filled with 0.5% biocytin. LTP was induced by low frequency stimulation (LFS) at 1Hz for 60～90 s, each pulse of the LFS paired with depolarization of post synaptic neuron to -20 mV.100 μmol/L APV, a kind of competitive NMDA receptor antagonist, was bath applied to some slices, and then the pairing protocol was performed to induce LTP. After APV wash out, LTP was induced and observed again. The neurons were stained after recording for the purpose of morphological study. The results were as following: ①The incidence of LTP was the highest (11/19) in 3 weeks group, second highest (7/14) in 4 weeks group, lowest (3/14) in 1 week group and increased a little (9/29) in 2 weeks group. The difference of LTP incidence between pre and post eye opening was significant ( P <0.05). LTP first occurred at postnatal 4 days. ②Compared with APV free group (24/54), APV application (4/33) significantly decreased the incidence of LTP ( P < 0.01 ). There were 5 pyramidal neurons without LTP induced when incubated with APV. However, LTP could be elicited in all the 5 cases following washout of the drug. In another 4 cases (all from Ⅳ～Ⅳ horizontal synapses), APV application could not block the LTP induction. It could be concluded that: ① The incidence of LTP of visual cortex was age and experience dependent and coincided well with the critical period of vision plasticity, indicating that LTP was a reflection of naturally occurring, experience dependent plasticity in the visual cortex. The patterned visual stimuli received after eye open might be an activation factor of the synaptic plasticity. ② LTP of visual cortex induced by LFS in layer Ⅳpaired with postsynaptic depolarization was NMDA receptor dependant during the critical period of visual plasticity. However, there was LTP existed in Ⅳ～Ⅳ horizontal synapses which could not be blocked by 100 μmol/L APV.
基金
国家自然科学基金资助项目 (3 9970 2 5 2
3 9770 2 5 8
3 0 0 70 2 5 4)
关键词
视皮层
发育
可塑性
长时程增强
全细胞记录
LTP
visual cortex
development
plasticity
long term potentiation
whole cell recording
rat
