Ludwig M, Leng G
Department of Physiology, University Medical School, Edinburgh, UK.
Eur J Neurosci. 1997 Dec;9(12):2532-40. doi: 10.1111/j.1460-9568.1997.tb01682.x.
To examine the role of endogenous vasopressin on the electrical activity of vasopressin neurons within the supraoptic nucleus of the rat brain in vivo, we have developed a novel technical approach for administering neuroactive drugs directly into the extracellular environment of the neuronal dendrites. A microdialysis probe was used for controlled local drug administration into the dendritic area of the nucleus during extracellular recording of single neurons in vivo. Vasopressin or selective V1 receptor antagonists were administered for between 10 and 30 min via a U-shaped microdialysis probe placed flat on the surface of the supraoptic nucleus after transpharyngeal exposure of the nucleus in urethane-anaesthetized rats. Microdialysis administration (retrodialysis) of vasopressin inhibited vasopressin neurons by reducing their firing rate, sometimes to total inactivity. Retrodialysis of V1-receptor antagonists partially reversed the effect of vasopressin, and a subsequent vasopressin administration was not effective in reducing the activity of these neurons, suggesting a receptor-mediated action of endogenous vasopressin. In addition, the duration of the periods of activity and the mean frequency during the active phase were increased in vasopressin neurons after retrodialysis of V1-receptor antagonist, indicating a physiological role of endogenous vasopressin. Neither vasopressin nor the antagonists altered the activity of continuously firing oxytocin neurons. Thus, vasopressin released within the supraoptic nucleus may act via V1 receptors located specifically on vasopressin neurons to regulate their phasic activity by an auto-inhibitory action. Since vasopressin release from the dendrites of vasopressin neurons is increased and prolonged after various forms of stimulation, it is proposed that this mechanism will act to limit excitation of vasopressin neurons, and hence secretion from the neurohypophysis. In addition, combined in vivo retrodialysis/ single cell recording allows controlled introduction of neuroactive substances into the extracellular fluid in the immediate vicinity of recorded neurons. This is shown to provide a novel approach to study neurotransmitter actions on supraoptic neurons in vivo.
为了研究内源性血管加压素对大鼠脑视上核内血管加压素神经元电活动的作用，我们开发了一种将神经活性药物直接注入神经元树突细胞外环境的新技术方法。在体内对单个神经元进行细胞外记录时，使用微透析探针将药物控制性地局部注入视上核的树突区域。在乌拉坦麻醉的大鼠经咽暴露视上核后，通过放置在视上核表面的U形微透析探针，给药血管加压素或选择性V1受体拮抗剂10至30分钟。通过微透析给药（逆向透析）血管加压素可降低血管加压素神经元的放电频率，从而抑制其活性，有时甚至使其完全停止活动。V1受体拮抗剂的逆向透析部分逆转了血管加压素的作用，随后再次给药血管加压素对降低这些神经元的活性无效，这表明内源性血管加压素具有受体介导的作用。此外，在V1受体拮抗剂逆向透析后，血管加压素神经元活动期的持续时间和活动期的平均频率增加，这表明内源性血管加压素具有生理作用。血管加压素和拮抗剂均未改变持续放电的催产素神经元的活性。因此，视上核内释放的血管加压素可能通过特异性位于血管加压素神经元上的V1受体，通过自身抑制作用调节其相位活动。由于在各种形式的刺激后，血管加压素神经元树突释放的血管加压素增加且持续时间延长，因此推测该机制将限制血管加压素神经元的兴奋，从而限制神经垂体的分泌。此外，体内联合逆向透析/单细胞记录可将神经活性物质控制性地引入记录神经元紧邻的细胞外液中。这被证明为研究体内神经递质对视上核神经元的作用提供了一种新方法。
