Bloms-Funke P, Gernert M, Ebert U, Löscher W
Department of Pharmacology, Toxicology, and Pharmacy, School of Veterinary Medicine, Bünteweg, Hannover, Germany.
J Neurosci Res. 1999 Mar 1;55(5):608-19. doi: 10.1002/(SICI)1097-4547(19990301)55:5<608::AID-JNR8>3.0.CO;2-9.
In epilepsy research, there is a growing interest in the role of the piriform cortex (PC) in the development and maintenance of limbic kindling and other types of limbic epileptogenesis leading to complex partial seizures. Neurophysiological studies on PC or amygdala-PC slice preparations from kindled rats showed that kindling of the amygdala induces long-lasting changes in synaptic efficacy in the ipsilateral PC, including spontaneous discharges and enhanced susceptibility of PC neurons to evoked burst responses. These long-lasting electrophysiological changes in the PC during kindling appear to be due, at least in part, to impaired function of gamma-aminobutyric acid (GABA)ergic interneurons. The aim of the present study was to develop an anesthetic protocol allowing electrophysiological single-unit recordings from inhibitory, presumably GABAergic PC interneurons in vivo. In addition to recording of spontaneously active PC neurons, microiontophoretic application of glutamate was used to activate silent neurons. Anesthesia of rats with ketamine/xylazine was not suited for single-unit recordings in the PC because of marked cardiovascular depression. Anesthesia with chloral hydrate allowed recording of spontaneous or glutamate-driven single-unit activity in approximately 40% of all animals. A similar percentage was obtained when recordings were done with the narcotic opioid fentanyl (plus gallamine), after all surgical preparations were performed under anesthesia with repeated administration of the barbiturate methohexital. To avoid brain accumulation of methohexital by repeated applications, we modified the anesthetic protocol in that methohexital was only injected once for initiation of surgical anesthesia, followed by the short-acting anesthetic propofol which does not accumulate upon repeated application. Again, after surgical preparation, electrophysiological recordings were done under fentanyl (plus gallamine). By this procedure, spontaneous or glutamate-driven single-unit activity could be measured in all rats in either layer II or III of the PC. Based on shape and frequency of action potentials, two types of neurons were recorded. The predominant type was similar in its firing characteristics to GABAergic neurons in other brain regions, was mainly located in layer III, and could be suppressed by the serotonin2A receptor antagonist MDL 100,907, suggesting that this type of PC neuron represents inhibitory, putative GABAergic interneurons. This new in vivo preparation may be useful for evaluation of PC neurons in kindled rats.
在癫痫研究中，梨状皮层（PC）在边缘叶点燃及其他导致复杂部分性发作的边缘叶癫痫发生发展和维持过程中的作用正受到越来越多的关注。对点燃大鼠的PC或杏仁核 - PC脑片标本进行的神经生理学研究表明，杏仁核点燃会引起同侧PC突触效能的持久变化，包括自发放电以及PC神经元对诱发爆发反应的易感性增强。在点燃过程中PC的这些持久电生理变化似乎至少部分归因于γ-氨基丁酸（GABA）能中间神经元的功能受损。本研究的目的是制定一种麻醉方案，以便在体内对推测为GABA能的抑制性PC中间神经元进行电生理单单位记录。除了记录自发活动的PC神经元外，还使用微量离子电泳施加谷氨酸来激活沉默神经元。用氯胺酮/赛拉嗪麻醉大鼠不适合在PC中进行单单位记录，因为会出现明显的心血管抑制。水合氯醛麻醉能使约40%的动物记录到自发或谷氨酸驱动的单单位活动。在用巴比妥类美索比妥反复给药麻醉下完成所有手术准备后，使用麻醉性阿片类芬太尼（加加拉明）进行记录时也获得了类似的百分比。为避免因反复应用美索比妥导致其在脑内蓄积，我们修改了麻醉方案，即美索比妥仅在开始手术麻醉时注射一次，随后使用短效麻醉剂丙泊酚，丙泊酚反复应用时不会蓄积。同样，在手术准备后，在芬太尼（加加拉明）麻醉下进行电生理记录。通过这种方法，可以在PC的II层或III层的所有大鼠中测量自发或谷氨酸驱动的单单位活动。根据动作电位的形状和频率，记录到了两种类型的神经元。主要类型在放电特征上与其他脑区的GABA能神经元相似，主要位于III层，并且可被5-羟色胺2A受体拮抗剂MDL 100,907抑制，这表明这种类型的PC神经元代表抑制性、推测为GABA能的中间神经元。这种新的体内制备方法可能有助于评估点燃大鼠中的PC神经元。
