Newby-Schmidt M B, Norton S
Neurotoxicology. 1981 Dec;2(4):743-8.
Analysis of walking of young chicks showed that morphine treatment of the chick embryo resulted in motor difficulties that depended on the timing of initial morphine exposure. Morphine sulfate was injected daily at a dose of 20 mg/kg egg into the air sac of viable eggs. Groups of eggs were treated starting on either day 12 or day 16 of incubation with either morphine or sterile water. Injections were continued through incubation day 19 and the eggs were allowed to hatch. The chicks started on morphine on day 16 showed signs of neuromuscular weakness at the posthatching age of 1-2 days. At 7 days of age they had a wider stride and greater angle of placement of the feet compared to both the controls, and to the chicks that were started on morphine on day 12. Since tolerance to morphine can develop in the chick embryo after only 4 daily injections, the chicks receiving morphine from day 12 may have been tolerant to the deleterious effects produced by morphine on locomotion at a critical period of motor development around day 16.
对幼雏行走的分析表明，对鸡胚进行吗啡处理会导致运动困难，这种困难取决于初次接触吗啡的时间。将硫酸吗啡以20毫克/千克鸡蛋的剂量每日注射到活鸡蛋的气室中。从孵化的第12天或第16天开始，用吗啡或无菌水对几组鸡蛋进行处理。注射持续到孵化第19天，然后让鸡蛋孵化。在孵化第16天开始使用吗啡的雏鸡在孵化后1至2天出现神经肌肉无力的迹象。与对照组以及在孵化第12天开始使用吗啡的雏鸡相比，7日龄时它们的步幅更宽，脚的放置角度更大。由于仅4次每日注射后鸡胚就能对吗啡产生耐受性，从孵化第12天开始接受吗啡的雏鸡可能在运动发育的关键时期（约第16天）对吗啡对运动产生的有害影响产生了耐受性。
