Moos F C, Rossi K, Richard P
CNRS-UPR9055 Biologie des Neurones Endocrines, Centre de Pharmacologie-Endocrinologie, Montpellier, France.
Neuroscience. 1997 Apr;77(4):993-1002. doi: 10.1016/s0306-4522(96)00536-2.
The control of suckling-induced bursting activity of oxytocin neurons and of phasic activity of vasopressin neurons by N-methyl-D-aspartate receptors was investigated in anaesthetized lactating rats. Receptor antagonist or agonist was applied in the vicinity of supraoptic neurons recorded extracellularly. The basal activity of oxytocin neurons was tonically decreased and increased by sustained application of the antagonist and agonist respectively. These effects occurred independently of the effectiveness of suckling to trigger the bursting pattern. When drugs were applied during an ongoing series of milk-ejection-related bursts, these changes were accompanied by parallel modifications in burst amplitude, but burst periodicity was unaffected. In rats failing to milk-eject, antagonist or agonist application did not facilitate the occurrence of bursts. Simultaneous recordings from oxytocin neurons in the contralateral supraoptic nucleus showed that neither their basal nor their bursting activity were affected, indicating the absence of cross-talk between nuclei during such application. The excitatory effect of N-methyl-D-aspartate differed from that induced in the same neurons by i.c.v. injection of oxytocin, which enhanced basal level of activity and burst amplitude, but also increased burst frequency. Furthermore, the distribution of interspike intervals indicated that N-methyl-D-aspartate, but not oxytocin, induced a regularization of the spike pattern. For vasopressin neurons, application of the receptor antagonist inhibited phasic activity by decreasing burst duration and increasing silences. Conversely, N-methyl-D-aspartate enhanced phasic activity, increasing both the duration of the active phases and the frequency of spikes during active phases. When applied to silent vasopressin neurons, N-methyl-D-aspartate induced a regular phasic activity. These results provide evidence that functional N-methyl-D-aspartate receptors regulate the excitability of both oxytocin and vasopressin neurons in lactating rats. These receptors play a paramount role in maintaining a certain level of basal activity which will favour appropriate discharge patterns, tonic for oxytocin neurons and phasic for vasopressin neurons. For oxytocin neurons, this sustained control by ambient glutamate influences the amplitude of bursts, but N-methyl-D-aspartate receptors are probably not involved in the generation of the bursting pattern.
在麻醉的泌乳大鼠中，研究了 N-甲基-D-天冬氨酸受体对催产素神经元的吸吮诱导爆发活动以及加压素神经元的相位活动的控制。将受体拮抗剂或激动剂应用于细胞外记录的视上核神经元附近。持续应用拮抗剂和激动剂分别使催产素神经元的基础活动呈紧张性降低和增加。这些效应的出现与吸吮触发爆发模式的有效性无关。当在一系列正在进行的与喷乳相关的爆发期间应用药物时，这些变化伴随着爆发幅度的平行改变，但爆发周期不受影响。在未能喷乳的大鼠中，应用拮抗剂或激动剂并未促进爆发的发生。对侧视上核中催产素神经元的同步记录表明，其基础活动和爆发活动均未受到影响，这表明在此类应用过程中核间不存在串扰。N-甲基-D-天冬氨酸的兴奋作用与脑室内注射催产素在相同神经元中诱导的作用不同，脑室内注射催产素可提高基础活动水平和爆发幅度，但也增加爆发频率。此外，峰间期的分布表明，N-甲基-D-天冬氨酸而非催产素诱导了放电模式的规则化。对于加压素神经元，应用受体拮抗剂通过缩短爆发持续时间和增加静息期来抑制相位活动。相反，N-甲基-D-天冬氨酸增强相位活动，增加活动期的持续时间和活动期内的放电频率。当应用于静息的加压素神经元时，N-甲基-D-天冬氨酸诱导出规则的相位活动。这些结果提供了证据，表明功能性 N-甲基-D-天冬氨酸受体调节泌乳大鼠中催产素和加压素神经元的兴奋性。这些受体在维持一定水平的基础活动中起着至关重要的作用，这将有利于适当的放电模式，催产素神经元为紧张性放电，加压素神经元为相位性放电。对于催产素神经元，周围谷氨酸的这种持续控制影响爆发幅度，但 N-甲基-D-天冬氨酸受体可能不参与爆发模式的产生。
