Rybak J, Meinertzhagen I A
Neuroscience Institute, Dalhousie University, Halifax, Nova Scotia, Canada.
Eur J Neurosci. 1997 Feb;9(2):319-33. doi: 10.1111/j.1460-9568.1997.tb01402.x.
The short-term influence of visual experience was studied in the first-order tetrad synapses of the first optic neuropil, or lamina, underlying the compound eye in the housefly (Musca domestica). We report the effects of single light reversals, in which flies reared in constant darkness were exposed to light or those in constant light were exposed to darkness, on this defined population of synapses. The synaptic population was characterized by quantitative electron microscopic methods using three parameters: (i) the number of synaptic contacts per photoreceptor terminal; (ii) the size of these synapses, given by the mean platform width of their presynaptic ribbons; and (iii) the proportion (up to approximately 20%) of small synapses-those having a ribbon platform less than 0.17 micron wide. The effects of light exposures in flies reared in constant darkness include decreased mean synaptic size and increased numbers of synapses. These effects are seen in flies of all ages (to 10 days). Long light exposures (2-6 h) are much less effective than short exposures (down to 20 s), with maximum effects obtained at 15 min (up to 45% more synapses). Small synapses are reasoned to be new junctions formed only recently; the decreased mean synaptic size and the increased number of synapses seen after short light exposures are both interpreted to result from a recent burst of synaptogenesis in the adult lamina. The effects of dark exposure in flies reared in constant light are the reciprocal of those seen in dark-reared flies exposed to light, but they are less pronounced. Although the function of such changes is not yet known, they may form part of the light adaptation mechanism of the photoreceptor, and occur along with a redistribution of other organelles involving membrane invaginations into its terminal. These changes occur against a background trend for control flies reared under constant conditions to have fewer, larger synapses with increasing age up to 10 days, an effect that is most pronounced in constant darkness, when synaptic number decreases by 21% and size increases by 13%.
我们研究了视觉经验对家蝇（Musca domestica）复眼下方第一视觉神经纤维层（即薄板层）中一阶四联突触的短期影响。我们报告了单次光反转的影响，即饲养在持续黑暗中的果蝇暴露于光下，或饲养在持续光照下的果蝇暴露于黑暗中，对这一特定突触群体的影响。通过定量电子显微镜方法，利用三个参数对突触群体进行了表征：（i）每个光感受器末端的突触接触数量；（ii）这些突触的大小，由其突触前带的平均平台宽度给出；（iii）小突触（即带平台宽度小于0.17微米的突触）的比例（高达约20%）。饲养在持续黑暗中的果蝇接受光照后的影响包括平均突触大小减小和突触数量增加。所有年龄段（至10天）的果蝇都出现了这些影响。长时间光照（2 - 6小时）的效果远不如短时间光照（短至20秒），在15分钟时获得最大效果（突触数量最多增加45%）。小突触被认为是最近才形成的新连接；短时间光照后平均突触大小减小和突触数量增加都被解释为是成年薄板层中近期突触形成爆发的结果。饲养在持续光照下的果蝇接受黑暗暴露的影响与饲养在黑暗中接受光照的果蝇的影响相反，但不太明显。尽管这种变化的功能尚不清楚，但它们可能构成光感受器光适应机制的一部分，并与其他细胞器的重新分布一起发生，这些细胞器涉及膜内陷到其末端。这些变化是在饲养在恒定条件下的对照果蝇随着年龄增长至10天，突触数量减少、突触变大这一背景趋势下发生的，这种影响在持续黑暗中最为明显，此时突触数量减少21%，大小增加13%。
