Otawa S, Takagi K, Ogawa H
Department of Physiology, Kumamoto University School of Medicine, Japan.
Exp Brain Res. 1995;106(3):391-402. doi: 10.1007/BF00231062.
Two main subclasses of ionotropic receptors for excitatory amino acids (EAAs), N-methyl-D-aspartate (NMDA) receptors and non-NMDA receptors, are involved in neurotransmission in the cortex of mammals. To examine whether EAAs are transmitters at the cortical taste area (CTA) in rats and to elucidate which types of the two ionotropic receptors operate at these synapses, we studied the effects of microiontophoretic administration of EAA antagonists on the responses of 64 taste cortical neurons to four basic taste stimuli in urethane-anesthetized rats. Both D-2-amino-5-phosphonovalerate (APV), a selective antagonist for NMDA receptors, and 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), a selective antagonist for non-NMDA receptors, suppressed most of the taste responses. The percentage of neurons suppressed by APV (70.3%) was almost the same as that suppressed by CNQX (64.1%). These suppressive effects were independent of the effects of background discharges during the prestimulus, water-rinsing period. The percentage of neurons suppressed by the antagonists did not differ between any pairs of taste stimuli. The number of neurons possessing both receptors was larger in the granular insular area (area GI), one of the two CTAs, than in the dysgranular insular area (area DI). In addition, taste responses were suppressed by CNQX or by both APV and CNQX in area GI in a significantly larger number of layer V neurons than in area DI. The present results indicate that normal excitatory transmission of taste afferents in the CTA in rats was mediated by both NMDA and non-NMDA receptors. The finding that a large fraction of neurons in the CTA in rats mediated taste information through NMDA receptors in normal transmission might be related to the higher potency of the plasticity observed in the CTA.
兴奋性氨基酸（EAA）的离子型受体主要有两个亚类，即N-甲基-D-天冬氨酸（NMDA）受体和非NMDA受体，它们参与哺乳动物皮质中的神经传递。为了研究EAA是否为大鼠皮质味觉区（CTA）的神经递质，并阐明这两种离子型受体中的哪些类型在这些突触起作用，我们研究了在氨基甲酸乙酯麻醉的大鼠中，通过微离子电泳给予EAA拮抗剂对64个味觉皮质神经元对四种基本味觉刺激的反应的影响。NMDA受体的选择性拮抗剂D-2-氨基-5-膦酰戊酸（APV）和非NMDA受体的选择性拮抗剂6-氰基-7-硝基喹喔啉-2,3-二酮（CNQX）都抑制了大部分味觉反应。被APV抑制的神经元百分比（70.3%）与被CNQX抑制的神经元百分比（64.1%）几乎相同。这些抑制作用与刺激前水洗期背景放电的影响无关。拮抗剂抑制的神经元百分比在任何一对味觉刺激之间没有差异。在两个CTA之一的颗粒状岛叶区（GI区）中，同时拥有两种受体的神经元数量比颗粒减少的岛叶区（DI区）更多。此外，在GI区，CNQX或APV与CNQX共同作用时，对V层神经元味觉反应的抑制作用在数量上显著多于DI区。目前的结果表明，大鼠CTA中味觉传入神经的正常兴奋性传递是由NMDA和非NMDA受体共同介导的。在正常传递过程中，大鼠CTA中很大一部分神经元通过NMDA受体介导味觉信息，这一发现可能与CTA中观察到的更高可塑性有关。
