Department of Pharmacology, University of Minnesota, 6-120 Jackson Hall, 321 Church St. S.E., Minneapolis, MN 55455-0217, USA.
J Pharmacol Exp Ther. 2012 Apr;341(1):115-25. doi: 10.1124/jpet.111.188235. Epub 2012 Jan 6.
Long-term use of opioids is hindered by respiratory depression and the possibility for fatal overdose in drug abusers. This is attributed to higher levels of tolerance that develops against antinociception than to respiratory depression. Identifying important mechanisms that would increase morphine respiratory depression and overdose tolerance could lead to the safer use of opioids. Because protein kinase C (PKC) activity mediates the development and maintenance of morphine antinociceptive tolerance, we hypothesized that activating PKCα or PKCε at the pre-Bötzinger complex (preBötC) can increase morphine tolerance in respiration and overdose. Laser microdissection and quantitative reverse transcriptase-polymerase chain reaction were used to compare the relative mRNA abundances of PKCα, γ, and ε between ventrolateral periaqueductal gray (vlPAG) and preBötC. To test whether PKCα or ε could enhance morphine tolerance in respiratory depression and overdose, lentivirus carrying the wild type, constitutively activated mutants, and small interference RNA against PKCα or ε was stereotaxically injected into the preBötC. Expression of constitutively active PKC (CAPKC) α or ε, but not wild-type PKC (WTPKC) α or ε, at the preBötC allowed rats to develop tolerance to morphine respiratory depression. In terms of lethality, expression of WTPKCε, CAPKCα, or CAPKCε at preBötC increased morphine tolerance to lethal overdose. CAPKCε-expressing rats developed the highest level of respiratory depression tolerance. Furthermore, when CAPKCε lentivirus was injected into the vlPAG, rats were able to develop significant antinociceptive tolerance at low doses of morphine that normally do not cause tolerance. The approach of increasing morphine respiratory depression and lethality tolerance by increasing PKCα or ε activity at preBötC could be used to make opioids safer for long-term use.
长期使用阿片类药物会受到呼吸抑制和药物滥用者致命过量的阻碍。这归因于对镇痛作用的耐受性高于呼吸抑制的水平更高。确定会增加吗啡呼吸抑制和过量耐受的重要机制可能会导致阿片类药物更安全的使用。由于蛋白激酶 C (PKC) 活性介导吗啡镇痛耐受的发展和维持，我们假设在 Pre-Bötzinger 复合体 (preBötC) 上激活 PKCα 或 PKCε 可以增加吗啡在呼吸和过量中的耐受。激光微切割和定量逆转录聚合酶链反应用于比较腹外侧导水管周围灰质 (vlPAG) 和 preBötC 之间 PKCα、γ 和 ε 的相对 mRNA 丰度。为了测试 PKCα 或 ε 是否可以增强吗啡在呼吸抑制和过量中的耐受，携带野生型、组成型激活突变体和针对 PKCα 或 ε 的小干扰 RNA 的慢病毒被立体定向注射到 preBötC 中。preBötC 中表达组成型激活的 PKC (CAPKC) α 或 ε，但不是野生型 PKC (WTPKC) α 或 ε，允许大鼠对吗啡呼吸抑制产生耐受。就致死性而言，preBötC 中 WTPKCε、CAPKCα 或 CAPKCε 的表达增加了吗啡对致死性过量的耐受。CAPKCε 表达的大鼠发展出最高水平的呼吸抑制耐受。此外，当 CAPKCε 慢病毒被注射到 vlPAG 中时，大鼠能够在通常不会引起耐受的低剂量吗啡下产生显著的镇痛耐受。通过增加 preBötC 中 PKCα 或 ε 的活性来增加吗啡呼吸抑制和致死性耐受的方法可用于使阿片类药物更安全地长期使用。
