Massari V J, Shirahata M, Johnson T A, Lauenstein J M, Gatti P J
Dept. of Pharmacology, Howard University, College of Medicine, Washington, DC 20059, USA.
Brain Res. 1998 Mar 2;785(2):329-40. doi: 10.1016/s0006-8993(97)01335-8.
Physiological and light microscopic evidence suggest that substance P (SP) may be a neurotransmitter contained in first-order sensory baroreceptor afferents; however, ultrastructural support for this hypothesis is lacking. We have traced the central projections of the carotid sinus nerve (CSN) in the cat by utilizing the transganglionic transport of horseradish peroxidase (HRP). The dorsolateral subnucleus of the nucleus tractus solitarius (dlNTS) was processed for the histochemical visualization of transganglionically labeled CSN afferents and for the immunocytochemical visualization of SP by dual labeling light and electron microscopic methods. Either HRP or SP was readily identified in single-labeled unmyelinated axons, myelinated axons, and nerve terminals in the dlNTS. SP immunoreactivity was also identified in unmyelinated axons, myelinated axons, and nerve terminals in the dlNTS, which were simultaneously identified as CSN primary afferents. However, only 15% of CSN terminals in the dlNTS were immunoreactive for SP. Therefore, while the ultrastructural data support the hypothesis that SP immunoreactive first-order neurons are involved in the origination of the baroreceptor reflex, they suggest that only a modest part of the total sensory input conveyed from the carotid sinus baroreceptors to the dlNTS is mediated by SP immunoreactive CSN terminals. Five types of axo-axonic synapses were observed in the dlNTS. SP immunoreactive CSN afferents were very rarely involved in these synapses. Furthermore, SP terminals were never observed to form the presynaptic element in an axo-axonic synapse with a CSN afferent. Therefore, SP does not appear to be involved in the modulation of the baroreceptor reflex in the dlNTS.
生理学和光学显微镜证据表明，P物质（SP）可能是一级感觉压力感受器传入神经中所含的一种神经递质；然而，这一假说缺乏超微结构方面的支持。我们通过利用辣根过氧化物酶（HRP）的跨神经节运输，追踪了猫的颈动脉窦神经（CSN）的中枢投射。采用双标记光镜和电镜方法，对孤束核背外侧亚核（dlNTS）进行处理，以对经跨神经节标记的CSN传入神经进行组织化学可视化，并对SP进行免疫细胞化学可视化。在dlNTS中，无论是HRP还是SP都很容易在单标记的无髓轴突、有髓轴突和神经终末中被识别出来。在dlNTS的无髓轴突、有髓轴突和神经终末中也鉴定出了SP免疫反应性，这些结构同时被鉴定为CSN初级传入神经。然而，dlNTS中只有15%的CSN终末对SP呈免疫反应性。因此，虽然超微结构数据支持SP免疫反应性一级神经元参与压力感受器反射起源的假说，但它们表明，从颈动脉窦压力感受器传导至dlNTS的全部感觉输入中，只有一小部分是由SP免疫反应性CSN终末介导的。在dlNTS中观察到了五种轴-轴突触类型。SP免疫反应性CSN传入神经很少参与这些突触。此外，从未观察到SP终末在与CSN传入神经形成的轴-轴突触中构成突触前成分。因此，SP似乎不参与dlNTS中压力感受器反射的调制。
