Bronstein D M, Przewlocki R, Akil H
Mental Health Research Institute, University of Michigan, Ann Arbor 48109-0720.
Brain Res. 1990 Jun 11;519(1-2):102-11. doi: 10.1016/0006-8993(90)90066-k.
In previous studies to determine whether chronic opiate administration might negatively feedback upon endogenous opioid systems in the CNS, investigators found no changes in steady-state concentrations of opioid peptides following morphine pelleting. However, since only steady-state levels were measured, it was still not clear whether morphine treatment altered the release and/or biosynthesis of opioid-containing neurons. The goal of the present study was to assess the effects of chronic morphine pelleting on the dynamics of beta-endorphin (beta E) biosynthesis in rats. Hence, at several times during a 7-day morphine treatment, concentrations of total beta E-immunoreactivity (-ir), as well as chromatographically sieved forms of beta E, were determined by RIA, and mRNA levels of pro-opiomelanocortin (POMC) were measured by a solution phase protection assay using a mouse or rat POMC 32P-labelled riboprobe. Concentrations of total beta E-ir or different forms of beta E-ir peptides (i.e. beta-lipotropin, beta E1-31, or beta E1-27/beta E1-26) in the hypothalamus or midbrain following either 1 or 7 days of treatment were similar in morphine- and placebo-pelleted animals. However, a significant increase in total hypothalamic beta E-ir was observed following 3 days of morphine pelleting; chromatographic analyses indicated that this was primarily due to a selective increase in the opiate inactive forms of beta E, i.e. beta E1-27/beta E1-26. After 7 days of pelleting, morphine-treated animals tended to have lower POMC mRNA levels than those of placebo controls (20 to 50% decrease in different studies). The accumulation of hypothalamic beta E-ir at 3 days, and the apparent decline in POMC mRNA levels at 7 days, lend support to the hypothesis that morphine negatively feeds back upon POMC neurons in the brain by inhibiting beta E release and biosynthesis.
在之前确定长期给予阿片类药物是否会对中枢神经系统内源性阿片系统产生负反馈的研究中，研究人员发现，在给予吗啡丸剂后，阿片肽的稳态浓度没有变化。然而，由于仅测量了稳态水平，因此仍不清楚吗啡治疗是否改变了含阿片类神经元的释放和/或生物合成。本研究的目的是评估长期给予吗啡丸剂对大鼠β-内啡肽（βE）生物合成动态的影响。因此，在7天吗啡治疗期间的几个时间点，通过放射免疫分析（RIA）测定总βE免疫反应性（-ir）的浓度以及βE的色谱筛选形式，并使用小鼠或大鼠POMC 32P标记的核糖探针通过溶液相保护测定法测量阿片促黑素皮质激素原（POMC）的mRNA水平。在治疗1天或7天后，吗啡丸剂处理组和安慰剂丸剂处理组动物下丘脑或中脑的总βE-ir或不同形式的βE-ir肽（即β-促脂素、βE1-31或βE1-27/βE1-26）浓度相似。然而，在给予吗啡丸剂3天后，观察到下丘脑总βE-ir显著增加；色谱分析表明，这主要是由于βE的阿片无活性形式即βE1-27/βE1-26选择性增加所致。在给予丸剂7天后，吗啡处理组动物的POMC mRNA水平往往低于安慰剂对照组（不同研究中降低20%至50%）。3天下丘脑βE-ir的积累以及7天POMC mRNA水平的明显下降，支持了吗啡通过抑制βE释放和生物合成对大脑中的POMC神经元产生负反馈的假说。
