Crain S M, Crain B, Peterson E R
Brain Res. 1986 Apr 2;370(1):61-72. doi: 10.1016/0006-8993(86)91105-4.
Exposure of fetal mouse spinal cord-ganglion explants to morphine (greater than 0.1 microM) results in naloxone-reversible, dose-dependent depression of sensory-evoked dorsal-horn synaptic-network responses within a few minutes. After chronic opiate exposure (1 microM) for 2-3 days, these dorsal cord responses recover and can then occur even in greater than 10 microM morphine. In the present study, when naive explants were treated with forskolin (10-50 microM)--a selective activate activator of cyclase (AC)--for 10-30 min prior to and during exposure to morphine (0.1-0.3 microM) or D-Ala2-D-Leu5-enkephalin (0.03-0.1 microM), the usual opioid depressant effects on dorsal-horn responses generally failed to occur (10-30 min tests). Dibutyryl cyclic AMP (10 microM) or the more lipid-soluble analog, dioctanoyl cyclic AMP (0.1 mM), produced a similar degree of subsensitivity to opiates as 10 microM forskolin. With high levels of forskolin (50 microM), even concentrations of morphine up to 1-10 microM were far less effective in depressing cord responses. These effects of exogenous cAMP analogs and forskolin on cord-ganglion explants are probably both mediated by increases in intracellular cAMP. The marked decrease in opioid sensitivity of cAMP or forskolin-treated cord-ganglion explants provides significant electrophysiologic data compatible with the hypothesis that neurons may develop tolerance and/or dependence during chronic opioid exposure by a compensatory enhancement of their AC/cAMP system following initial opioid depression of AC activity. Previous evidence relied primarily on behavioral tests and biochemical analyses of cell cultures. It will be of interest to determine if dorsal-horn tissues of cord-ganglion explants do, in fact, develop increased AC/cAMP levels as they express physiologic signs of tolerance during chronic exposure to opioids.
将胎鼠脊髓神经节外植体暴露于吗啡（大于0.1微摩尔），几分钟内即可导致纳洛酮可逆的、剂量依赖性的感觉诱发背角突触网络反应抑制。在慢性阿片类药物暴露（1微摩尔）2 - 3天后，这些脊髓背侧反应恢复，然后即使在大于10微摩尔的吗啡环境中也能出现。在本研究中，当未接触过药物的外植体在暴露于吗啡（0.1 - 0.3微摩尔）或D - Ala2 - D - Leu5 - 脑啡肽（0.03 - 0.1微摩尔）之前及期间，用福司可林（10 - 50微摩尔）——一种环化酶（AC）的选择性激活剂——处理10 - 30分钟时，阿片类药物对背角反应通常的抑制作用一般不会出现（10 - 30分钟测试）。二丁酰环磷酸腺苷（10微摩尔）或更具脂溶性的类似物，二辛酰环磷酸腺苷（0.1毫摩尔），产生了与10微摩尔福司可林类似程度的对阿片类药物的敏感性降低。使用高浓度的福司可林（50微摩尔）时，即使浓度高达1 - 10微摩尔的吗啡在抑制脊髓反应方面也效果大打折扣。外源性环磷酸腺苷类似物和福司可林对脊髓神经节外植体的这些作用可能都是通过细胞内环磷酸腺苷的增加介导的。环磷酸腺苷或福司可林处理的脊髓神经节外植体对阿片类药物敏感性的显著降低提供了重要的电生理数据，与以下假设相符：在慢性阿片类药物暴露期间，神经元可能通过在阿片类药物最初抑制AC活性后对其AC/环磷酸腺苷系统进行代偿性增强而产生耐受性和/或依赖性。先前的证据主要依赖于行为测试和细胞培养的生化分析。确定脊髓神经节外植体的背角组织在慢性暴露于阿片类药物期间表现出耐受性生理迹象时，其AC/环磷酸腺苷水平是否确实升高将是很有意义的。
