Jakab R L, Leranth C
Department of Obstetrics and Gynecology Yale University, School of Medicine, New Haven, CT 06510.
Exp Brain Res. 1993;92(3):420-30. doi: 10.1007/BF00229030.
In the lateral septal area (LSA), both inhibitory and excitatory dopamine (DA) actions, as well as hypothalamic and midbrain DA efferents, have been described. Some neurons of the hypothalamic and midbrain DA systems contain somatostatin (SOM) or neurotensin (NT), and, in the LSA, the distribution of fibers containing these peptides overlaps with DA fibers. These data prompted us to test for the presence of SOM and NT in LSA dopaminergic axon terminals of hypothalamic and midbrain origins. To verify the origins of SOM and NT innervation of the LSA, the retrograde tracer horseradish peroxidase conjugated with wheat germ agglutinin (HRP-WGA) was injected into the LSA, and alternate brain sections were immunostained for SOM, NT, or tyrosine hydroxylase (TH) in group 1 rats. Numerous retrogradely labeled neurons were found immunopositive for SOM in the periventricular and basolateral hypothalamus, many HRP-WGA labeled cells contained NT immunoreactivity in the ventral tegmental area, and TH-immunoreactive retrogradely labeled neurons were observed in both brain areas. In a new approach, the presence of these peptides in dopaminergic boutons was assessed by combining peptide immunocytochemistry with acute 6-hydroxydopamine (6-OHDA) induced lesioning of DA cell groups. These groups of rats were treated with desipramine to protect the noradrenergic fibers, and 45 min later 1 microgram 6-OHDA (in 0.5 microliter saline) was unilaterally injected into the periventricular hypothalamus (group 2) or the ventral tegmental area (group 3). After 48 h the rats were killed and alternate septal sections of both groups were immunostained for TH, SOM, or NT. On the operated side of the LSA in both groups, electron microscopy revealed numerous axon terminals that were immunopositive for TH and contained autophagous cytolysosomes, an early sign of catecholamine fiber degeneration induced by 6-OHDA. In group 2, phagosome-containing boutons were found immunopositive for SOM, but not for NT; vice versa, in group 3, only NT-positive degenerated boutons were detected. SOM- and NT-positive degenerated axon terminals in both groups formed synaptic contacts with LSA neurons, in particular with somatospiny cells. On the contralateral side of the LSA, all of the axon terminals were intact. It has been shown that SOM exerts an inhibitory action, whereas NT has an excitatory effect on limbic area neurons. Thus, the results implicate that the differential peptide content of dopamine fibers marks their functional differences. It appears that LSA neurons receive double innervation from an inhibitory "somatostatinergic" DA system of the hypothalamus, and from an excitatory "neurotensinergic" DA system of the midbrain.
在外侧隔区（LSA），已描述了多巴胺（DA）的抑制性和兴奋性作用，以及下丘脑和中脑的DA传出纤维。下丘脑和中脑DA系统的一些神经元含有生长抑素（SOM）或神经降压素（NT），并且在LSA中，含有这些肽的纤维分布与DA纤维重叠。这些数据促使我们检测下丘脑和中脑起源的LSA多巴胺能轴突终末中SOM和NT的存在。为了验证LSA中SOM和NT神经支配的起源，将与小麦胚凝集素结合的逆行示踪剂辣根过氧化物酶（HRP-WGA）注入LSA，并对第1组大鼠的交替脑切片进行SOM、NT或酪氨酸羟化酶（TH）免疫染色。在室周和基底外侧下丘脑发现许多逆行标记的神经元对SOM呈免疫阳性，在腹侧被盖区许多HRP-WGA标记的细胞含有NT免疫反应性，并且在两个脑区均观察到TH免疫反应性逆行标记的神经元。在一种新方法中，通过将肽免疫细胞化学与急性6-羟基多巴胺（6-OHDA）诱导的DA细胞群损伤相结合，评估这些肽在多巴胺能突触小体中的存在。这些组的大鼠用去甲丙咪嗪治疗以保护去甲肾上腺素能纤维，45分钟后将1微克6-OHDA（溶于0.5微升盐水中）单侧注入室周下丘脑（第2组）或腹侧被盖区（第3组）。48小时后处死大鼠，对两组的交替隔区切片进行TH、SOM或NT免疫染色。在两组LSA的手术侧，电子显微镜显示大量轴突终末对TH呈免疫阳性，并含有自噬性溶酶体，这是6-OHDA诱导的儿茶酚胺纤维变性的早期迹象。在第2组中，发现含有吞噬体的突触小体对SOM呈免疫阳性，但对NT不呈免疫阳性；反之，在第3组中，仅检测到NT阳性的变性突触小体。两组中SOM和NT阳性的变性轴突终末与LSA神经元形成突触联系，特别是与躯体棘状细胞形成突触联系。在LSA的对侧，所有轴突终末均完整无损。已表明SOM发挥抑制作用，而NT对边缘区神经元具有兴奋作用。因此，结果表明多巴胺纤维中不同的肽含量标志着它们的功能差异。似乎LSA神经元接受来自下丘脑抑制性“生长抑素能”DA系统和中脑兴奋性“神经降压素能”DA系统的双重神经支配。
