Keegan Bradley M T, Beveridge Thomas J R, Pezor Jeffrey J, Xiao Ruoyu, Sexton Tammy, Childers Steven R, Howlett Allyn C
Center for the Neurobiology of Addiction Treatment, Winston-Salem, NC 27157, USA; Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA.
Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA; Department of Chemistry, Wake Forest University, Winston-Salem, NC 27157, USA.
Neuropharmacology. 2015 Aug;95:492-502. doi: 10.1016/j.neuropharm.2015.02.021. Epub 2015 Feb 25.
The GABAB receptor is a therapeutic target for CNS and neuropathic disorders; however, few preclinical studies have explored effects of chronic stimulation. This study evaluated acute and chronic baclofen treatments on GABAB-activated G-proteins and signaling protein phosphorylation as indicators of GABAB signaling capacity. Brain sections from rats acutely administered baclofen (5 mg/kg, i.p.) showed no significant differences from controls in GABAB-stimulated GTPγS binding in any brain region, but displayed significantly greater phosphorylation/activation of focal adhesion kinase (pFAK(Tyr397)) in mesocorticolimbic regions (caudate putamen, cortex, hippocampus, thalamus) and elevated phosphorylated/activated glycogen synthase kinase 3-β (pGSK3β(Tyr216)) in the prefrontal cortex, cerebral cortex, caudate putamen, nucleus accumbens, thalamus, septum, and globus pallidus. In rats administered chronic baclofen (5 mg/kg, t.i.d. for five days), GABAB-stimulated GTPγS binding was significantly diminished in the prefrontal cortex, septum, amygdala, and parabrachial nucleus compared to controls. This effect was specific to GABAB receptors: there was no effect of chronic baclofen treatment on adenosine A1-stimulated GTPγS binding in any region. Chronically-treated rats also exhibited increases in pFAK(Tyr397) and pGSK3β(Tyr216) compared to controls, and displayed wide-spread elevations in phosphorylated dopamine- and cAMP-regulated phosphoprotein-32 (pDARPP-32(Thr34)) compared to acutely-treated or control rats. We postulate that those neuroadaptive effects of GABAB stimulation mediated by G-proteins and their sequelae correlate with tolerance to several of baclofen's effects, whereas sustained signaling via kinase cascades points to cross-talk between GABAB receptors and alternative mechanisms that are resistant to desensitization. Both desensitized and sustained signaling pathways should be considered in the development of pharmacotherapies targeting the GABA system.
GABAB受体是中枢神经系统和神经性疾病的治疗靶点；然而，很少有临床前研究探讨慢性刺激的影响。本研究评估了急性和慢性巴氯芬治疗对GABAB激活的G蛋白和信号蛋白磷酸化的影响，以此作为GABAB信号传导能力的指标。急性给予巴氯芬（5mg/kg，腹腔注射）的大鼠脑切片在任何脑区的GABAB刺激的GTPγS结合方面与对照组均无显著差异，但在中脑边缘区域（尾状壳核、皮质、海马体、丘脑）显示出粘着斑激酶（pFAK(Tyr397)）的磷酸化/激活显著增加，并且在前额叶皮质、大脑皮质、尾状壳核、伏隔核、丘脑、隔区和苍白球中糖原合酶激酶3-β（pGSK3β(Tyr216)）的磷酸化/激活升高。在给予慢性巴氯芬（5mg/kg，每日三次，共五天）的大鼠中，与对照组相比，前额叶皮质、隔区、杏仁核和臂旁核中GABAB刺激的GTPγS结合显著减少。这种效应是GABAB受体特有的：慢性巴氯芬治疗对任何区域的腺苷A1刺激的GTPγS结合均无影响。与对照组相比，慢性治疗的大鼠还表现出pFAK(Tyr397)和pGSK3β(Tyr216)增加，并且与急性治疗或对照大鼠相比，磷酸化的多巴胺和cAMP调节磷蛋白-32（pDARPP-32(Thr34)）广泛升高。我们推测，由G蛋白介导的GABAB刺激的那些神经适应性效应及其后遗症与对巴氯芬几种效应的耐受性相关，而通过激酶级联的持续信号传导表明GABAB受体与抗脱敏的替代机制之间存在相互作用。在开发针对GABA系统的药物疗法时，应考虑脱敏和持续信号传导途径。
