Ostrowski N L, Burke T R, Rice K C, Pert A, Pert C B
Brain Res. 1987 Feb 3;402(2):275-86. doi: 10.1016/0006-8993(87)90034-5.
Cyclofoxy, a fluorinated analog of naltrexone, has been designed specifically to permit in vivo labeling of opiate receptors in experimental animals and ultimately, humans. Recently, using positron emission tomography (PET), 3-[18F]acetylcyclofoxy was shown to accumulate in opiate receptor-rich brain regions of a live baboon and to be stereospecifically displaced by injections of (-)-naloxone but not (+)-naloxone. Autoradiographic evidence is presented here that the unacetylated compound, [3H]cyclofoxy, labels a population of opiate receptors in brain after in vivo injections that is virtually identical to that labeled by [3H]naloxone. The in vivo binding patterns of [3H]cyclofoxy in brain were similar to those obtained following incubation of slide-mounted brain sections in vitro. Intravenous injections of [3H]cyclofoxy to rats yielded high (greater than 4:1) striatal and thalamic to cerebellar binding ratios in brain homogenates, supernatants and in 24 micron-thick brain sections 60 min after 30 mu Ci per animal (spec. act. = 16.4 Ci/mmol). Autoradiographs revealed the typical opiate antagonist binding profile with marked retention of [3H]cyclofoxy in the striatal patches, subcallosal streak, medial habenula and central thalamus with little retention of label in cerebellum. [3H]Cyclofoxy binding was reversible since the radiolabeled drug disappeared from brain tissue within 2 h after injections to rats, or could be removed from brain slices in vitro by washing slide-mounted tissue sections for 45 min. In addition, after in vitro washing the same brain sections again bound [3H]cyclofoxy or [3H]naloxone in the same pattern. When pre-washed brain sections were incubated with [3H]cyclofoxy in the presence of unlabeled naloxone, [3H]cyclofoxy binding was reduced to background levels. These data show that [3H]cyclofoxy labels-sensitive opiate receptors in vivo and in vitro. The present results combined with evidence that cyclofoxy demonstrates a low level of toxicity in animals suggest that cyclofoxy is an excellent tool with which to study the physiological role of opiate receptors in living animals using in vivo autoradiography, and in humans using PET.
环福可昔，一种纳曲酮的氟化类似物，被专门设计用于在实验动物乃至最终在人体中对阿片受体进行体内标记。最近，利用正电子发射断层扫描（PET）技术，显示3-[18F]乙酰环福可昔在一只活狒狒富含阿片受体的脑区中蓄积，并且可被注射（-）-纳洛酮而非（+）-纳洛酮立体特异性取代。本文提供了放射自显影证据，即未乙酰化的化合物[3H]环福可昔在体内注射后可标记脑中的一群阿片受体，这与[3H]纳洛酮标记的受体群几乎相同。[3H]环福可昔在脑中的体内结合模式与体外孵育载玻片上的脑切片后获得的模式相似。给大鼠静脉注射[3H]环福可昔后，在每只动物注射30 μCi（比活度 = 16.4 Ci/mmol）60分钟后，脑匀浆、上清液以及厚度为24微米的脑切片中，纹状体与丘脑和小脑的结合比很高（大于4:1）。放射自显影片显示出典型的阿片拮抗剂结合图谱，[3H]环福可昔在纹状体斑块、胼胝体下条纹、内侧缰核和丘脑中央有明显滞留，而在小脑中几乎没有滞留。[3H]环福可昔的结合是可逆的，因为注射到大鼠体内后2小时内，放射性标记药物从脑组织中消失，或者在体外通过将载玻片上的组织切片洗涤45分钟可从脑切片中去除。此外，体外再次洗涤相同的脑切片后，其又以相同模式结合[3H]环福可昔或[3H]纳洛酮。当预先洗涤的脑切片在未标记的纳洛酮存在下与[3H]环福可昔一起孵育时，[3H]环福可昔的结合降低至背景水平。这些数据表明[3H]环福可昔在体内和体外均可标记对其敏感的阿片受体。目前的结果加上环福可昔在动物中显示出低毒性水平的证据表明，环福可昔是一种极好的工具，可用于利用体内放射自显影技术在活体动物中研究阿片受体的生理作用，并利用PET技术在人体中进行研究。
