Prusky G T, Shaw C, Cynader M S
Department of Psychology, Dalhousie University, Halifax, NS, Canada.
Brain Res. 1988 Apr 1;467(2):161-76. doi: 10.1016/0165-3806(88)90020-x.
In vitro autoradiographic techniques using [3H]nicotine were used to characterise nicotine binding sites in developing kitten visual cortex. These binding sites in adult animals have a Bmax of 3.91 fmol/mg protein and a Kd of 4.40 nM. Displacement experiments indicate that [3H]nicotine binds to a nicotinic receptor site that is similar to central nicotinic sites described by investigators in other mammals. The number of binding sites increases during postnatal development, peaking near 60 days of age and levelling-off thereafter. There is no evidence for large changes in affinity during postnatal development for this binding site. [3H]Nicotine binding sites are densely concentrated in layer IV in the visual cortex of adult animals, with sharply reduced binding outside of cortical areas 17 and 18. This laminar pattern does not change during postnatal development, but an increase in the number of binding sites in layer IV as well as in layers I and VI occurs during early postnatal life. These binding sites disappear when extrinsic cortical inputs are severed. However, they survive when neurons in the visual cortex are selectively destroyed with a cell-specific neurotoxin. Unilateral destruction of the lateral geniculate nucleus eliminates [3H]nicotine binding sites in the visual cortex ipsilateral to the lesion, suggesting that they are located presynaptically on the terminals of lateral geniculate nucleus afferent fibres. The laminar pattern of binding of [3H]nicotine during early development of the visual cortex is complimentary to that for muscarinic acetylcholine receptors. These latter receptors redistribute during postnatal development becoming less prominent in layer IV at the same time as the [3H]nicotine binding sites are increasing in number in this layer. For a short period of time at the height of the critical period for cortical plasticity, both populations of binding sites are located in layer IV.
利用[3H]尼古丁的体外放射自显影技术来表征发育中小猫视觉皮层中的尼古丁结合位点。成年动物中的这些结合位点的最大结合容量（Bmax）为3.91飞摩尔/毫克蛋白质，解离常数（Kd）为4.40纳摩尔。置换实验表明，[3H]尼古丁与一种烟碱样受体位点结合，该位点类似于其他哺乳动物研究人员所描述的中枢烟碱样位点。结合位点的数量在出生后发育过程中增加，在60日龄左右达到峰值，此后趋于平稳。在出生后发育过程中，没有证据表明该结合位点的亲和力有大的变化。[3H]尼古丁结合位点在成年动物视觉皮层的IV层中密集分布，在皮层17区和18区之外结合明显减少。这种分层模式在出生后发育过程中不变，但在出生后早期，IV层以及I层和VI层中的结合位点数量增加。当切断外在皮层输入时，这些结合位点消失。然而，当用细胞特异性神经毒素选择性破坏视觉皮层中的神经元时，它们仍然存在。外侧膝状体核的单侧破坏消除了损伤同侧视觉皮层中的[3H]尼古丁结合位点，表明它们位于外侧膝状体核传入纤维的突触前末端。视觉皮层早期发育过程中[3H]尼古丁结合的分层模式与毒蕈碱型乙酰胆碱受体的分层模式互补。后一种受体在出生后发育过程中重新分布，在IV层中变得不那么突出，与此同时，该层中[3H]尼古丁结合位点的数量正在增加。在皮层可塑性关键期的高峰期的短时间内，这两种结合位点都位于IV层。
