Centre for Neuroendocrinology, Department of Physiology, University of Otago School of Medical Sciences, Dunedin 9054, New Zealand.
J Neurosci. 2013 Jul 31;33(31):12689-97. doi: 10.1523/JNEUROSCI.0579-13.2013.
Information processing by neurons has been traditionally envisioned to occur in discrete neuronal compartments. Specifically, dendrites receive and integrate synaptic inputs while axons initiate and conduct spikes to distal neuronal targets. We report here in mice, using morphological reconstructions and electrophysiology, that the gonadotropin-releasing hormone (GnRH) neurons that control mammalian fertility do not conform to this stereotype and instead possess a single projection structure that functions simultaneously as an axon and dendrite. Specifically, we show that the GnRH neuron projection to the median eminence to control pituitary hormone secretion possesses a spike initiation site and conducts action potentials while also exhibiting spines and synaptic appositions along its entire length. Classical axonal or dendritic markers are not detectable in the projection process. Activation of ionotropic glutamate and/or GABA receptors along the GnRH neuron projection is capable of depolarizing the membrane potential and initiating action potentials. In addition, focal glutamate application to the projection is able to regulate the width of propagating spikes. These data demonstrate that GnRH neurons elaborate a previously uncharacterized neuronal projection that functions simultaneously as an axon and dendrite. This structure, termed a "dendron," greatly expands the dynamic control of GnRH secretion into the pituitary portal system to regulate fertility.
神经元的信息处理一直被传统地设想发生在离散的神经元隔室中。具体而言，树突接收和整合突触输入，而轴突起始并传导至远端神经元靶标。我们在这里在小鼠中报告，使用形态重建和电生理学，控制哺乳动物生育能力的促性腺激素释放激素 (GnRH) 神经元不符合这种刻板印象，而是具有单一的投射结构，同时作为轴突和树突发挥作用。具体来说，我们表明， GnRH 神经元投射到正中隆起以控制垂体激素分泌，具有起始尖峰的部位并传导动作电位，同时在其整个长度上还表现出棘突和突触贴合。在投射过程中检测不到经典的轴突或树突标记物。沿着 GnRH 神经元投射激活离子型谷氨酸和/或 GABA 受体能够去极化膜电位并起始动作电位。此外，向投射物施加局部谷氨酸能够调节传播尖峰的宽度。这些数据表明，GnRH 神经元精心构建了一种以前未被表征的神经元投射，它同时作为轴突和树突发挥作用。这种结构称为“树突”，极大地扩展了 GnRH 分泌到垂体门脉系统的动态控制，以调节生育能力。
