Giovannini M G, Mutolo D, Bianchi L, Michelassi A, Pepeu G
Department of Preclinical and Clinical Pharmacology, University of Florence, Italy.
J Neurosci. 1994 Mar;14(3 Pt 1):1358-65. doi: 10.1523/JNEUROSCI.14-03-01358.1994.
The modulation of the septohippocampal cholinergic pathway by glutamatergic or GABAergic inputs was studied by monitoring the outflow of ACh collected via a transversal microdialysis probe implanted into the hippocampus and other brain areas of freely moving rats. In one set of experiments a transversal microdialysis membrane was inserted in the dorsal hippocampus, drugs were administered intracerebroventricularly through a cannula implanted in the lateral ventricle, and ACh outflow in the dialysate was measured by an HPLC method with an electrochemical detector. The dialysis membrane was usually perfused with Ringer's solution containing 7 microM physostigmine sulfate. Intracerebroventricular injections of the NMDA antagonists 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP; 1-50 nmol), MK801 (0.5-20 nmol), and D(-)-2-amino-7-phosphonoheptanoic acid (100 nmol) brought about an increase in hippocampal ACh outflow while the non-NMDA antagonist 6,7-dinitroquinoxaline-2,3-dione (0.25-20 nmol) was without effect. The increase in ACh outflow following CPP administration was dose dependent and reached a maximum of about 500%. It was abolished by TTX (0.5 microM) delivered locally to the hippocampus via the dialysis membrane and prevented by intracerebroventricular injection of the GABA agonist muscimol (5 nmol). In a second set of experiments, one microdialysis membrane was inserted in the dorsal hippocampus to detect ACh outflow and another in the septum to administer drugs locally and at the same time detect septal GABA outflow. The septal dialysis membrane was perfused with Ringer's solution without physostigmine, and GABA levels in the dialysate were measured by an HPLC method with a fluorescence detector. CPP (100 microM) perfused through the septum resulted in a decrease in septal GABA outflow and a concomitant increase in hippocampal ACh outflow. Muscimol (100 microM) administration into the septum abolished the effect of CPP on hippocampal ACh outflow but did not affect septal GABA outflow. These results demonstrate that in the septum NMDA receptors tonically activate GABAergic neurons which in turn inhibit the cholinergic septohippocampal neurons.
通过监测经植入自由活动大鼠海马体及其他脑区的横向微透析探针收集到的乙酰胆碱（ACh）流出量，研究了谷氨酸能或γ-氨基丁酸能（GABAergic）输入对隔海马胆碱能通路的调节作用。在一组实验中，将横向微透析膜插入背侧海马体，通过植入侧脑室的套管进行脑室内给药，并采用带电化学检测器的高效液相色谱法（HPLC）测量透析液中的ACh流出量。透析膜通常用含有7微摩尔硫酸毒扁豆碱的林格氏溶液灌注。脑室内注射N-甲基-D-天冬氨酸（NMDA）拮抗剂3-((RS)-2-羧基哌嗪-4-基)-丙基-1-膦酸（CPP；1 - 50纳摩尔）、MK801（0.5 - 20纳摩尔）和D(-)-2-氨基-7-膦庚酸（100纳摩尔）可使海马体ACh流出量增加，而非NMDA拮抗剂6,7-二硝基喹喔啉-2,3-二酮（0.25 - 20纳摩尔）则无此作用。CPP给药后ACh流出量的增加呈剂量依赖性，最高可达约500%。通过透析膜局部给予海马体的河豚毒素（TTX，0.5微摩尔）可消除这种增加，脑室内注射GABA激动剂蝇蕈醇（5纳摩尔）可预防这种增加。在第二组实验中，一个微透析膜插入背侧海马体以检测ACh流出量，另一个插入隔区以局部给药并同时检测隔区GABA流出量。隔区透析膜用不含毒扁豆碱的林格氏溶液灌注，采用带荧光检测器的HPLC法测量透析液中的GABA水平。通过隔区灌注CPP（100微摩尔）可导致隔区GABA流出量减少，同时海马体ACh流出量增加。向隔区注射蝇蕈醇（100微摩尔）可消除CPP对海马体ACh流出量的影响，但不影响隔区GABA流出量。这些结果表明，在隔区，NMDA受体持续激活GABA能神经元，进而抑制胆碱能隔海马神经元。
