Ennis M, Aston-Jones G, Shiekhattar R
Department of Anatomy and Cell Biology, University of Cincinnati College of Medicine, OH 45267-0521.
Brain Res. 1992 Dec 11;598(1-2):185-95. doi: 10.1016/0006-8993(92)90182-9.
The nucleus paragigantocellularis (PGi), located in the rostral ventrolateral medulla, is one of two major afferents to the nucleus locus coeruleus (LC). Electrical stimulation of PGi exerts a robust, predominantly excitatory influence on LC neurons that is blocked by intracerebroventricular (i.c.v.) administration of the broad spectrum excitatory amino acid (EAA) antagonists kynurenic acid (KYN) or gamma-D-glutamylglycine (DGG), but not by the selective N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-7-phosphonoheptanoate (AP7). I.c.v. injection of KYN or DGG also blocked activation of LC neurons evoked by noxious somatosensory stimuli. These results indicate that activation of LC neurons by PGi and noxious stimuli may be mediated by an EAA acting at a non-NMDA receptor in LC. In the present study, microiontophoretic techniques were used to determine the sensitivity of LC neurons in vivo to the selective EAA receptor agonists kainate (KA), NMDA and quisqualate (QUIS). Microinfusion and microiontophoresis were also used to determine whether direct application of KYN, the preferential non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3 dione (CNQX) or the selective NMDA receptor antagonist 2-amino-5-phosphonovalerate (AP5) onto LC neurons blocked excitation elicited by stimulation of PGi or the sciatic nerve. The results demonstrated that individual LC neurons were robustly activated by direct application of KA, NMDA and QUIS. Iontophoretically applied KYN reduced or completely antagonized responses evoked by all 3 agonists. In contrast, iontophoretically applied AP5 strongly attenuated NMDA-evoked excitation, while KA-and QUIS-evoked responses were not affected by this agent. Furthermore, direct application of KYN or the specific non-NMDA receptor antagonist, CNQX, onto LC neurons substantially attenuated or completely blocked synaptic activation produced by PGi or sciatic nerve stimulation in nearly every LC neuron tested. Microinfusion of the selective NMDA receptor antagonist AP5 had no effect on sciatic nerve-evoked responses. These results confirm our hypothesis that activation of LC neurons from PGi is mediated by an EAA operating primarily at a non-NMDA receptor subtype on LC neurons. Furthermore, these findings provide additional support for the hypothesis that this pathway mediates at least some sensory-evoked responses of LC neurons.
巨细胞旁核（PGi）位于延髓嘴侧腹外侧，是去甲肾上腺素能蓝斑核（LC）的两大主要传入神经之一。电刺激PGi对LC神经元产生强烈的、主要为兴奋性的影响，脑室内（i.c.v.）注射广谱兴奋性氨基酸（EAA）拮抗剂犬尿氨酸（KYN）或γ-D-谷氨酰甘氨酸（DGG）可阻断这种影响，但选择性N-甲基-D-天冬氨酸（NMDA）受体拮抗剂2-氨基-7-磷酸庚酸（AP7）则不能。脑室内注射KYN或DGG也可阻断伤害性躯体感觉刺激诱发的LC神经元激活。这些结果表明，PGi和伤害性刺激对LC神经元的激活可能由作用于LC中非NMDA受体的一种EAA介导。在本研究中，采用微离子电泳技术来确定体内LC神经元对选择性EAA受体激动剂海人藻酸（KA）、NMDA和quisqualate（QUIS）的敏感性。还采用微量注射和微离子电泳来确定直接将KYN、优先非NMDA受体拮抗剂6-氰基-7-硝基喹喔啉-2,3-二酮（CNQX）或选择性NMDA受体拮抗剂2-氨基-5-磷酸戊酸（AP5）应用于LC神经元是否能阻断PGi或坐骨神经刺激所引发的兴奋。结果表明，直接应用KA、NMDA和QUIS可强烈激活单个LC神经元。离子电泳应用的KYN可降低或完全拮抗所有3种激动剂所诱发的反应。相反，离子电泳应用的AP5可强烈减弱NMDA诱发的兴奋，而KA和QUIS诱发的反应不受该药物影响。此外，直接将KYN或特异性非NMDA受体拮抗剂CNQX应用于LC神经元，在几乎每个受试的LC神经元中，均可显著减弱或完全阻断PGi或坐骨神经刺激所产生的突触激活。微量注射选择性NMDA受体拮抗剂AP5对坐骨神经诱发的反应无影响。这些结果证实了我们的假设，即PGi对LC神经元的激活由主要作用于LC神经元上非NMDA受体亚型的一种EAA介导。此外，这些发现为该通路介导LC神经元至少部分感觉诱发反应的假设提供了额外支持。
