Miner Leeann H, Schroeter Sally, Blakely Randy D, Sesack Susan R
Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
J Comp Neurol. 2003 Nov 24;466(4):478-94. doi: 10.1002/cne.10898.
The prefrontal cortex (PFC) is a likely site of action for the therapeutic efficacy of antidepressants that inhibit norepinephrine (NE) reuptake. Moreover, drugs that block the NE transporter (NET) increase extracellular levels of both NE and dopamine (DA), an interaction that may contribute to their therapeutic properties. To examine the subcellular localization of NET and to investigate the spatial relationships between presumed NE and DA axons within the rat prelimbic PFC, we combined immunogold-silver localization of NET with immunoperoxidase staining for the catecholamine synthetic enzyme tyrosine hydroxylase (TH). An additional aim was to quantify the proportion of profiles dually labeled for NET and TH to test the common observation that TH immunolabeling is relatively selective for DA axons. NET-immunoreactive (NET-ir) axonal profiles were typically unmyelinated and occasionally were observed to form symmetric axodendritic synapses. The majority of immunogold NET labeling was unexpectedly observed in the cytoplasm rather than on the plasma membrane. Furthermore, in tissue dually labeled for both NET and TH, only 8-10% of profiles contained both markers. Unlike observations for singly labeled profiles, gold-silver particles for NET in dually labeled axons were localized primarily to the plasmalemma. A systematic survey of terminals labeled only for TH revealed that they were typically separated by at least 1.2 mum from NET-ir varicosities, and the two profile types were not seen to contact common targets. These results suggest that, in the rat PFC, NE axons (1) contain predominantly cytoplasmic NET, (2) infrequently contain TH immunolabeling, and (3) may interact with probable DA afferents by means of extrasynaptic mechanisms.
前额叶皮质（PFC）可能是抑制去甲肾上腺素（NE）再摄取的抗抑郁药发挥治疗作用的部位。此外，阻断NE转运体（NET）的药物会增加NE和多巴胺（DA）的细胞外水平，这种相互作用可能有助于其治疗特性。为了研究NET的亚细胞定位，并探究大鼠前边缘PFC中假定的NE和DA轴突之间的空间关系，我们将NET的免疫金银定位与儿茶酚胺合成酶酪氨酸羟化酶（TH）的免疫过氧化物酶染色相结合。另一个目的是量化NET和TH双重标记的轮廓比例，以验证TH免疫标记对DA轴突相对具有选择性这一普遍观察结果。NET免疫反应性（NET-ir）轴突轮廓通常无髓鞘，偶尔可观察到形成对称的轴树突触。出乎意料的是，大多数免疫金标记的NET出现在细胞质中，而非质膜上。此外，在NET和TH双重标记的组织中，只有8%-10%的轮廓同时含有这两种标记物。与单标记轮廓的观察结果不同，双重标记轴突中NET的金银颗粒主要定位于质膜。对仅标记TH的终末进行系统调查发现，它们通常与NET-ir膨体至少相隔1.2μm，且未观察到这两种轮廓类型接触共同靶点。这些结果表明，在大鼠PFC中，NE轴突（1）主要含有细胞质NET，（2）很少含有TH免疫标记，（3）可能通过突触外机制与可能的DA传入纤维相互作用。
