Division of Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands.
PLoS One. 2012;7(8):e43054. doi: 10.1371/journal.pone.0043054. Epub 2012 Aug 13.
Within the GABA(A)-receptor field, two important questions are what molecular mechanisms underlie benzodiazepine tolerance, and whether tolerance can be ascribed to certain GABA(A)-receptor subtypes.
We investigated tolerance to acute anxiolytic, hypothermic and sedative effects of diazepam in mice exposed for 28-days to non-selective/selective GABA(A)-receptor positive allosteric modulators: diazepam (non-selective), bretazenil (partial non-selective), zolpidem (α(1) selective) and TPA023 (α(2/3) selective). In-vivo binding studies with [(3)H]flumazenil confirmed compounds occupied CNS GABA(A) receptors.
Chronic diazepam treatment resulted in tolerance to diazepam's acute anxiolytic, hypothermic and sedative effects. In mice treated chronically with bretazenil, tolerance to diazepam's anxiolytic and hypothermic, but not sedative, effects was seen. Chronic zolpidem treatment resulted in tolerance to diazepam's hypothermic effect, but partial anxiolytic tolerance and no sedative tolerance. Chronic TPA023 treatment did not result in tolerance to diazepam's hypothermic, anxiolytic or sedative effects.
OUR DATA INDICATE THAT: (i) GABA(A)-α(2)/α(3) subtype selective drugs might not induce tolerance; (ii) in rodents quantitative and temporal variations in tolerance development occur dependent on the endpoint assessed, consistent with clinical experience with benzodiazepines (e.g., differential tolerance to antiepileptic and anxiolytic actions); (iii) tolerance to diazepam's sedative actions needs concomitant activation of GABA(A)-α(1)/GABA(A)-α(5) receptors. Regarding mechanism, in-situ hybridization studies indicated no gross changes in expression levels of GABA(A) α(1), α(2) or α(5) subunit mRNA in hippocampus or cortex. Since selective chronic activation of either GABA(A) α(2), or α(3) receptors does not engender tolerance development, subtype-selective GABA(A) drugs might constitute a promising class of novel drugs.
在 GABA(A) 受体领域，有两个重要问题，即苯二氮䓬类药物耐受的分子机制是什么，以及耐受是否可以归因于某些 GABA(A) 受体亚型。
我们研究了在 28 天内暴露于非选择性/选择性 GABA(A) 受体正变构调节剂的小鼠中，地西泮的急性抗焦虑、解热和镇静作用的耐受情况：地西泮（非选择性）、布仑扎尼（部分非选择性）、唑吡坦（α(1) 选择性）和 TPA023（α(2/3) 选择性）。用 [(3)H]氟马西尼进行体内结合研究证实了化合物占据了中枢神经系统 GABA(A) 受体。
慢性地西泮治疗导致地西泮急性抗焦虑、解热和镇静作用的耐受。在慢性用布仑扎尼治疗的小鼠中，观察到地西泮的抗焦虑和解热作用的耐受，但没有镇静作用的耐受。慢性唑吡坦治疗导致地西泮解热作用的耐受，但部分抗焦虑耐受和无镇静耐受。慢性 TPA023 治疗不会导致地西泮解热、抗焦虑或镇静作用的耐受。
我们的数据表明：(i) GABA(A)-α(2)/α(3) 亚型选择性药物可能不会引起耐受；(ii) 在啮齿动物中，根据所评估的终点，定量和时间上的耐受发展存在差异，这与苯二氮䓬类药物的临床经验一致（例如，对抗癫痫和抗焦虑作用的不同耐受）；(iii) 地西泮镇静作用的耐受需要同时激活 GABA(A)-α(1)/GABA(A)-α(5) 受体。关于机制，原位杂交研究表明，海马体或皮质中 GABA(A)α(1)、α(2)或α(5)亚基 mRNA 的表达水平没有明显变化。由于选择性慢性激活 GABA(A)α(2)或α(3)受体不会引起耐受的发展，因此亚型选择性 GABA(A) 药物可能构成一类有前途的新型药物。
