Szabo B, Dörner L, Pfreundtner C, Nörenberg W, Starke K
Institut für Pharmakologie und Toxikologie, Albert-Ludwigs-Universität, Freiburg i, Br., Germany.
Neuroscience. 1998 Jul;85(2):395-403. doi: 10.1016/s0306-4522(97)00597-6.
Electrophysiological consequences of activation of cannabinoid receptors have been mostly investigated on neuronal cell lines and on cells transfected with cannabinoid receptors. The aim of the present experiments was to study cannabinoid effects on identified neurons in situ. Electrically-evoked postsynaptic currents and voltage-dependent calcium currents were investigated in the principal neurons of the corpus striatum, the medium spiny neurons, with the patch-clamp method for brain slices. These neurons were chosen because they produce messenger RNA for cannabinoid receptors and because the density of cannabinoid binding sites in the striatum is high. Activation of muscarinic receptors by carbachol (10(-5) M) reduced inhibitory postsynaptic current amplitude by 67%. The synthetic cannabinoid receptor agonist R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4- benzoxazin-yl]-(1-naphtalenyl)methanone (WIN55212-2; 10(-8) to 10(-5) M) dose-dependently reduced striatal inhibitory postsynaptic currents; the maximum effect, inhibition by 52%, was observed at 10(-6) M. Another cannabinoid agonist, (-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydr oxypropyl)cyclohexanol (CP55940; 10(-6) M), also reduced inhibitory postsynaptic currents, by 50%. The CB1 cannnabinoid receptor antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)4-methyl-3-pyra zolecarboxamide (SR141716A; 10(-6) M) had no effect when given alone but abolished the effect of WIN55212-2 (10(-6) M). WIN55212-2 (10(-6) M) did not change the current evoked by the GABA(A)-receptor agonist muscimol (10(-6) M). Activation of muscarinic receptors by carbachol (10(-5) M) inhibited voltage-dependent calcium currents by 21%, but the cannabinoid receptor agonist WIN55212-2 (10(-6) M) was without effect. The results show that activation of CB1 cannabinoid receptors reduces GABAergic inhibitory postsynaptic currents in medium spiny neurons of the corpus striatum: the likely mechanism is presynaptic inhibition of GABA release from terminals of recurrent axons of the medium spiny neurons themselves.
大麻素受体激活的电生理后果大多是在神经元细胞系以及转染了大麻素受体的细胞上进行研究的。本实验的目的是研究大麻素对原位已鉴定神经元的作用。采用脑片膜片钳方法，研究了纹状体主要神经元即中等棘状神经元的电诱发突触后电流和电压依赖性钙电流。选择这些神经元是因为它们能产生大麻素受体的信使核糖核酸，且纹状体中大麻素结合位点的密度很高。卡巴胆碱（10⁻⁵ M）激活毒蕈碱受体可使抑制性突触后电流幅度降低67%。合成大麻素受体激动剂R(+)-[2,3-二氢-5-甲基-3-[(吗啉基)甲基]吡咯并[1,2,3-de]-1,4-苯并恶嗪基]-(1-萘基)甲酮（WIN55212-2；10⁻⁸至10⁻⁵ M）剂量依赖性地降低纹状体抑制性突触后电流；在10⁻⁶ M时观察到最大效应，抑制率为52%。另一种大麻素激动剂(-)-顺式-3-[2-羟基-4-(1,1-二甲基庚基)苯基]-反式-4-(3-羟丙基)环己醇（CP55940；10⁻⁶ M）也使抑制性突触后电流降低了50%。CB1大麻素受体拮抗剂N-哌啶基-5-(4-氯苯基)-1-(2,4-二氯苯基)-4-甲基-3-吡唑甲酰胺（SR141716A；10⁻⁶ M）单独给药时无作用，但可消除WIN55212-2（10⁻⁶ M）的作用。WIN55212-2（10⁻⁶ M）不改变GABA(A)受体激动剂蝇蕈醇（10⁻⁶ M）诱发的电流。卡巴胆碱（10⁻⁵ M）激活毒蕈碱受体可使电压依赖性钙电流抑制21%，但大麻素受体激动剂WIN55212-2（10⁻⁶ M）无此作用。结果表明，CB1大麻素受体的激活可降低纹状体中等棘状神经元的GABA能抑制性突触后电流：可能的机制是对中等棘状神经元自身回返轴突终末释放GABA的突触前抑制。
