Szabo Bela, Than Marta, Thorn David, Wallmichrath Ilka
Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität, Albertstrasse 25, D-79104 Freiburg i. Br., Germany.
J Pharmacol Exp Ther. 2004 Sep;310(3):915-25. doi: 10.1124/jpet.104.066670. Epub 2004 May 3.
The hypothesis of the present work was that activation of CB1 cannabinoid receptors inhibits GABAergic neurotransmission between basket and Purkinje cells in the cerebellar cortex. The aim was to test this hypothesis under near-physiological conditions. Action potentials of basket cells and spontaneous inhibitory postsynaptic currents (sIPSCs) in synaptically coupled Purkinje cells were recorded simultaneously in rat brain slices. The cannabinoid agonists (R)-(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl) methyl] pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone mesylate (WIN 55212-2) and (-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)-phenyl]-trans-4-(3-hydroxy-propyl)-cyclohexanol (CP55940) decreased the amplitude of sIPSCs occurring simultaneously with basket cell action potentials and lowered the success rate of synaptic transmission. These effects were prevented by the CB1 receptor antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichloro-phenyl)-4-methyl-3-pyrazole-carboxamide (SR141716). Depolarization of Purkinje cells also led to suppression of neurotransmission; prevention of this suppression by CP55940 and SR141716 indicates that endocannabinoids released from Purkinje cells were involved. WIN 55212-2 lowered the amplitude of autoreceptor currents recorded in basket cells (autoreceptor currents are due to the action of GABA released from axon terminals on GABAA autoreceptors of the same axon terminals); this is novel proof of the presynaptic action of cannabinoids. Autoreceptor current experiments also indicated that endogenous cannabinoids are not released by basket cell axon terminals. A presynaptic action is additionally supported by the observation that WIN 55212-2 lowered the frequency of miniature IPSCs recorded in the presence of tetrodotoxin and the calcium ionophore ionomycin. In conclusion, activation of CB1 receptors by exogenous cannabinoids and by endogenous cannabinoids released by Purkinje cells presynaptically inhibits GABAergic neurotransmission between basket and Purkinje cells. This was demonstrated under near-physiological conditions: transmitter release was elicited by action potentials generated by spontaneously firing intact presynaptic neurons.
本研究的假设是，CB1大麻素受体的激活会抑制小脑皮质中篮状细胞与浦肯野细胞之间的GABA能神经传递。目的是在接近生理条件下验证这一假设。在大鼠脑片中同时记录篮状细胞的动作电位和突触耦合浦肯野细胞中的自发抑制性突触后电流（sIPSCs）。大麻素激动剂（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)甲酮甲磺酸盐（WIN 55212-2）和（-）-顺式-3-[2-羟基-4-(1,1-二甲基庚基)-苯基]-反式-4-(3-羟基丙基)-环己醇（CP55940）降低了与篮状细胞动作电位同时出现的sIPSCs的幅度，并降低了突触传递的成功率。这些效应被CB1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（SR141716）所阻断。浦肯野细胞的去极化也导致神经传递的抑制；CP55940和SR141716对这种抑制的阻断表明，浦肯野细胞释放的内源性大麻素参与其中。WIN 55212-2降低了篮状细胞中记录到的自身受体电流的幅度（自身受体电流是由于轴突终末释放的GABA对同一轴突终末的GABAA自身受体的作用所致）；这是大麻素突触前作用的新证据。自身受体电流实验还表明，内源性大麻素不是由篮状细胞轴突终末释放的。WIN 55212-2降低了在河豚毒素和钙离子载体离子霉素存在下记录到的微小IPSCs的频率，这一观察结果进一步支持了突触前作用。总之，外源性大麻素和浦肯野细胞释放的内源性大麻素对CB1受体的激活在突触前抑制了篮状细胞与浦肯野细胞之间的GABA能神经传递。这是在接近生理条件下得到证明的：神经递质释放是由完整的自发放电突触前神经元产生的动作电位引发的。
