Zagon A, Terenzi M G, Roberts M H
Department of Physiology, University of Wales, College of Cardiff, U.K.
Neuroscience. 1995 Mar;65(1):253-72. doi: 10.1016/0306-4522(94)00468-k.
The anterior pretectal nucleus has recently been implicated in the descending modulation of nociception. Electrical stimulation of the nucleus was found to reduce the nociceptive responses of deep dorsal horn neurons and to inhibit spinally integrated withdrawal reflexes. It is believed that at least part of the descending inhibitory effects of the anterior pretectal nucleus are mediated by reticulospinal cells of the ventrolateral medulla. The purpose of the present study was to trace the direct medullary projections of the anterior pretectal nucleus, to describe their topographical organization and to reveal the chemical nature of some of their putative target cells. The connections were studied using anterograde tract-tracing with Phaseolus vulgaris leucoagglutinin. Direct projections from the anterior pretectal nucleus to the ipsilateral rostral ventral medulla were found in all cases. A dense innervation of the dorsal inferior olive, the gigantocellular reticular nucleus pars ventralis and pars alpha and the ventral pontine reticular nucleus was found from all aspects of the anterior pretectal nucleus. Descending labelled terminals were also observed in the gigantocellular reticular nucleus proper and, laterally, in the lateral paragigantocellular nucleus and in the region of the A5 noradrenergic cell group. A relatively lower density of labelled terminals was noted in the medullary raphe nuclei and in the rostroventrolateral reticular nucleus. Following tract-tracer injections into five distinct subregions of the anterior pretectal nucleus, the topographical organization of the projection was examined and the relatively highest density and most widespread projection was found to originate from the caudoventral part of the anterior pretectal nucleus. A combined tract-tracing and immunolabelling study revealed that some of the descending, labelled terminals were in close proximity of tyrosine hydroxylase-immunoreactive dendrites in the C1 and A5 cell groups. Some labelled fibres were also noted among the serotonin-immunoreactive cells in the lateral extension of the B3 cell population. The existence of direct projections to the ventral medulla and pons correlates well with physiological data which showed that the descending, antinociceptive effects of the anterior pretectal nucleus are relayed via the rostral ventrolateral medulla. The data are also in keeping with pharmacological studies that suggested the role of catecholaminergic cells in the mediation of these descending effects. It is proposed that the rostral ventral medullary projections provide a path through which antinociceptive effects of the anterior pretectal nucleus are mediated to the spinal cord.
前顶盖前核最近被认为与伤害性感受的下行调制有关。研究发现，电刺激该核可降低背角深层神经元的伤害性反应，并抑制脊髓整合的退缩反射。据信，前顶盖前核的下行抑制作用至少部分是由延髓腹外侧的网状脊髓细胞介导的。本研究的目的是追踪前顶盖前核的直接延髓投射，描述其拓扑结构，并揭示其一些假定靶细胞的化学性质。使用菜豆白细胞凝集素进行顺行束路追踪研究连接情况。在所有病例中均发现了从前顶盖前核到同侧延髓吻侧腹侧的直接投射。从前顶盖前核的各个方面都发现了对下橄榄背侧、巨细胞网状核腹侧部和α部以及脑桥腹侧网状核的密集神经支配。在巨细胞网状核本身以及外侧的外侧旁巨细胞核和A5去甲肾上腺素能细胞群区域也观察到了下行标记终末。在延髓中缝核和吻侧腹外侧网状核中发现标记终末的密度相对较低。在前顶盖前核的五个不同亚区域注射束路示踪剂后，检查了投射的拓扑结构，发现投射密度相对最高且分布最广的区域来自前顶盖前核的尾腹侧部分。一项联合束路追踪和免疫标记研究表明，一些下行标记终末与C1和A5细胞群中酪氨酸羟化酶免疫反应性树突紧密相邻。在B3细胞群外侧延伸部分的5-羟色胺免疫反应性细胞之间也注意到一些标记纤维。存在到延髓腹侧和脑桥的直接投射与生理学数据很好地相关，生理学数据表明前顶盖前核的下行抗伤害感受作用是通过延髓吻侧腹侧中继的。这些数据也与药理学研究一致，药理学研究表明儿茶酚胺能细胞在这些下行作用的介导中起作用。有人提出，延髓吻侧腹侧投射提供了一条通路，通过该通路前顶盖前核的抗伤害感受作用被介导至脊髓。
