Condés-Lara Miguel, Martínez-Lorenzana Guadalupe, Rojas-Piloni Gerardo, Rodríguez-Jiménez Javier
Departamento de Neurobiología del Desarrollo y Neurofisiología, Instituto de Neurobiología, Universidad Nacional Autónoma de México, Campus UNAM Juriquilla, México.
Brain Res. 2007 Jul 30;1160:20-9. doi: 10.1016/j.brainres.2007.05.031. Epub 2007 May 26.
The paraventricular nucleus (PVN) of the hypothalamus is an interesting structure with diverse functions due to its different neuronal populations, neurotransmitters, and projections to other central nervous system structures. The PVN is a primary source of oxytocin (OT) in the central nervous system. In fact, a direct PVN projection to the spinal cord has been demonstrated by retrograde and anterograde tracers, and more than the 50% of this projection is oxytocinergic. This OT descending projection is proposed to be an endogenous system that controls the nociceptive information arriving at the spinal cord. However, we have no information about the specific organization of the OT descending innervations to the different spinal cord segments. The aim of the present study was to determine whether the projecting PVN neurons arrive at cervical regions and then continue to lumbar regions. That is, we sought to establish if the OT projecting cells have a topic or a diffuse projection in order to obtain histological data to support the endogenous OT diffuse mechanism of analgesia described elsewhere. With this purpose in mind we combined the OT immunohistochemistry technique with retrograde neuronal tracers in the spinal cord. We applied Diamidino Yellow (DY) for the superficial dorsal horn cervical segments and True Blue (TB) for the lumbar segments. Data were collected from eight rats with well-placed injections. We only used the animals in which the tracer deposits were confined to superficial layers I and II of the dorsal horn. A mainly ipsilateral projection was observed, but stained neurons were also observed in the contralateral PVN. A large fraction of the stained PVN cells was doubled labeled but some were single labeled. Combining the retrograde tracer techniques and the OT detection procedure, we observed triple-labeled neurons. The present results demonstrate that PVN neurons send collaterals at least to the superficial cervical and lumbar segments of the dorsal horn of the spinal cord. Moreover, some of these stained cells use OT as a neurotransmitter. These results are of great relevance since they demonstrate that the PVN plays an important role in the somatosensorial system, and they support anatomic evidence of an endogenous mechanism involved in analgesia. Finally, we also describe median raphe nucleus double-labeled cells (DY+TB) signaling diffuse descending projections for this largely studied nucleus that are involved in endogenous analgesia.
下丘脑室旁核（PVN）是一个有趣的结构，因其不同的神经元群体、神经递质以及与其他中枢神经系统结构的投射关系而具有多种功能。PVN是中枢神经系统中催产素（OT）的主要来源。事实上，逆行和顺行示踪剂已证实PVN有直接投射到脊髓的通路，且该投射通路中超过50%是催产素能的。这种OT下行投射被认为是一个内源性系统，可控制到达脊髓的伤害性信息。然而，我们对OT下行神经支配在不同脊髓节段的具体组织情况尚无了解。本研究的目的是确定投射到PVN的神经元是否先到达颈段区域，然后继续延伸至腰段区域。也就是说，我们试图确定OT投射细胞是具有特定的投射模式还是弥散性投射，以便获取组织学数据来支持其他地方所描述的内源性OT弥散性镇痛机制。出于这个目的，我们将OT免疫组织化学技术与脊髓中的逆行神经元示踪剂相结合。我们将双脒基黄（DY）应用于颈段脊髓背角浅层，将真蓝（TB）应用于腰段脊髓。从八只注射部位良好的大鼠收集数据。我们仅使用示踪剂沉积局限于背角浅层I和II层的动物。观察到主要是同侧投射，但在对侧PVN中也观察到了染色神经元。大部分染色的PVN细胞是双重标记的，但也有一些是单一标记的。结合逆行示踪技术和OT检测程序，我们观察到了三重标记的神经元。目前的结果表明，PVN神经元至少向脊髓背角的颈段和腰段浅层发送侧支。此外，这些染色细胞中的一些使用OT作为神经递质。这些结果具有重要意义，因为它们表明PVN在躯体感觉系统中发挥着重要作用，并且支持了参与镇痛的内源性机制的解剖学证据。最后，我们还描述了中缝核的双重标记细胞（DY+TB），它们标记了这个在很大程度上已被研究的、参与内源性镇痛的核团的弥散性下行投射。
