Smotherman W P, Robinson S R
Department of Psychology, Binghamton University, New York 13902-6000.
Behav Neurosci. 1994 Oct;108(5):951-61. doi: 10.1037//0735-7044.108.5.951.
Milk promotes activity in the kappa opioid system of the rat fetus that reduces responsiveness to cutaneous stimulation. In this study, fetuses on Gestational Day 20 were presented with an artificial nipple (conditioned stimulus; CS) paired with an intraoral infusion of milk (unconditioned stimulus; US). One paired presentation of the CS and US reduced fetal responsiveness after reexposure to the CS. Selective antagonism of opioid receptors after conditioning indicated that reduced responsiveness was due to mu opioid activity. Mu and kappa opioid activity was evident after 3 paired presentations of CS and US and reexposure to milk. Kappa opioid activity during conditioning was necessary for mu involvement after reexposure to the CS or US. These experiments, which were conducted with fetal subjects that lacked suckling experience, suggest that neurochemical systems engaged during suckling may change rapidly after the newborn's initial experiences at the nipple.
牛奶会促进大鼠胎儿κ阿片系统的活性，从而降低其对皮肤刺激的反应性。在本研究中，给妊娠第20天的胎儿提供一个人工乳头（条件刺激；CS），并同时经口输注牛奶（非条件刺激；US）。CS和US配对呈现一次后，再次暴露于CS时胎儿的反应性降低。条件反射后对阿片受体的选择性拮抗表明，反应性降低是由于μ阿片活性所致。CS和US配对呈现3次并再次暴露于牛奶后，μ和κ阿片活性均很明显。再次暴露于CS或US后，条件反射期间的κ阿片活性是μ阿片参与所必需的。这些实验是在缺乏哺乳经验的胎儿受试者身上进行的，表明哺乳过程中参与的神经化学系统可能在新生儿最初在乳头的经历后迅速发生变化。
