Oka Y, Matsushima T
Zoological Institute, Faculty of Science, University of Tokyo, Japan.
J Neurosci. 1993 May;13(5):2161-76. doi: 10.1523/JNEUROSCI.13-05-02161.1993.
Modulation of ionic channel properties and synaptic functions by neurotransmitters and hormones is called neuro-modulation and may be the basis for many long-lasting changes in animal behavior, for example, changes in the arousal or motivational states. We have previously shown in a teleost, the dwarf gourami, that the terminal nerve (TN) cells are a major component of the gonadotropin-releasing hormone (GnRH) system and are structurally independent from the preoptic/hypophysial-GnRH system, which projects to the pituitary and facilitates gonadotropin release from the gonadotropes. While GnRH fibers originating from TN cells are distributed widely throughout the brain, they do not project to the pituitary. Thus, TN-GnRH system does not function as a hypophysiotropic hormone but probably as a neuro-modulator, capable of affecting widespread regions of the brain. In the present study, we used a whole-brain in vitro preparation to examine the spontaneous electrical activities of TN-GnRH cells and to determine the morphology of individual cells by intracellular injections of either neurobiotin or biocytin. The recorded cells were clearly identified as GnRH-immunoreactive TN cells by using combined intracellular injection and GnRH immunocytochemistry. Most of the TN cells showed endogenous slow (1-7 Hz), regular beating discharges. The intrinsic nature of this activity was demonstrated by the voltage dependency of the beating frequency, rhythm resetting, and persistence of rhythmicity after synaptic isolation. Only a small number of TN cells showed either irregular or bursting discharge patterns. Anatomical observation of intracellularly labeled cells showed that, regardless of discharge patterns, all the TN cells had multiple axonal branches that project to those areas where we had previously demonstrated dense GnRH-immunoreactive fibers. From the present results, we propose a hypothesis that may be relevant to the peptidergic and monoaminergic neuromodulatory systems in general. The modulator neurons have endogenous rhythmic activities that vary according to the animal's hormonal or environmental conditions, and they regulate the excitability of target neurons in a wide variety of brain regions simultaneously via multiple axonal branches.
神经递质和激素对离子通道特性及突触功能的调节被称为神经调节，它可能是动物行为中许多长期变化的基础，例如觉醒或动机状态的改变。我们之前在一种硬骨鱼——侏儒 Gourami 中发现，终末神经（TN）细胞是促性腺激素释放激素（GnRH）系统的主要组成部分，并且在结构上独立于视前区/垂体 - GnRH 系统，后者投射到垂体并促进促性腺激素从促性腺细胞释放。虽然源自 TN 细胞的 GnRH 纤维广泛分布于整个大脑，但它们并不投射到垂体。因此，TN - GnRH 系统并不作为促垂体激素发挥作用，而可能作为一种神经调节剂，能够影响大脑的广泛区域。在本研究中，我们使用全脑体外制备方法来检测 TN - GnRH 细胞的自发电活动，并通过细胞内注射神经生物素或生物胞素确定单个细胞的形态。通过联合细胞内注射和 GnRH 免疫细胞化学，记录的细胞被明确鉴定为 GnRH 免疫反应性 TN 细胞。大多数 TN 细胞表现出内源性缓慢（1 - 7Hz）、规则的搏动放电。这种活动的内在特性通过搏动频率的电压依赖性、节律重置以及突触隔离后节律性的持续得以证明。只有少数 TN 细胞表现出不规则或爆发性放电模式。对细胞内标记细胞的解剖学观察表明，无论放电模式如何，所有 TN 细胞都有多个轴突分支，这些分支投射到我们之前证明有密集 GnRH 免疫反应性纤维的区域。基于目前的结果，我们提出了一个可能与一般肽能和单胺能神经调节系统相关的假设。调节神经元具有内源性节律活动，其根据动物的激素或环境条件而变化，并且它们通过多个轴突分支同时调节广泛脑区中靶神经元的兴奋性。
