Kalló Imre, Molnár Csilla S, Szöke Sarolta, Fekete Csaba, Hrabovszky Erik, Liposits Zsolt
Laboratory of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences Budapest, Hungary ; Faculty of Information Technology and Bionics, Pázmány Péter Catholic University Budapest, Hungary.
Laboratory of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences Budapest, Hungary.
Front Neuroanat. 2015 Sep 4;9:112. doi: 10.3389/fnana.2015.00112. eCollection 2015.
The ventral tegmental area (VTA) is a main regulator of reward and integrates a wide scale of hormonal and neuronal information. Feeding-, energy expenditure-, stress, adaptation- and reproduction-related hypothalamic signals are processed in the VTA and influence the reward processes. However, the neuroanatomical origin and chemical phenotype of neurons mediating these signals to the VTA have not been fully characterized. In this study we have systematically mapped hypothalamic neurons that project to the VTA using the retrograde tracer Choleratoxin B subunit (CTB) and analyzed their putative gamma-aminobutyric acid (GABA) and/or glutamate character with in situ hybridization in male rats. 23.93 ± 3.91% of hypothalamic neurons projecting to the VTA was found in preoptic and 76.27 ± 4.88% in anterior, tuberal and mammillary hypothalamic regions. Nearly half of the retrogradely-labeled neurons in the preoptic, and more than one third in the anterior, tuberal and mammillary hypothalamus appeared in medially located regions. The analyses of vesicular glutamate transporter 2 (VGLUT2) and glutamate decarboxylase 65 (GAD65) mRNA expression revealed both amino acid markers in different subsets of retrogradely-labeled hypothalamic neurons, typically with the predominance of the glutamatergic marker VGLUT2. About one tenth of CTB-IR neurons were GAD65-positive even in hypothalamic nuclei expressing primarily VGLUT2. Some regions were populated mostly by GAD65 mRNA-containing retrogradely-labeled neurons. These included the perifornical part of the lateral hypothalamus where 58.63 ± 19.04% of CTB-IR neurons were GABAergic. These results indicate that both the medial and lateral nuclear compartments of the hypothalamus provide substantial input to the VTA. Furthermore, colocalization studies revealed that these projections not only use glutamate but also GABA for neurotransmission. These GABAergic afferents may underlie important inhibitory mechanism to fine-tune the reward value of specific signals in the VTA.
腹侧被盖区(VTA)是奖赏的主要调节者,整合了广泛的激素和神经元信息。与进食、能量消耗、应激、适应和繁殖相关的下丘脑信号在VTA中被处理,并影响奖赏过程。然而,介导这些信号至VTA的神经元的神经解剖学起源和化学表型尚未完全明确。在本研究中,我们使用逆行示踪剂霍乱毒素B亚基(CTB)系统地绘制了投射至VTA的下丘脑神经元图谱,并在雄性大鼠中通过原位杂交分析了它们假定的γ-氨基丁酸(GABA)和/或谷氨酸特性。发现投射至VTA的下丘脑神经元中,23.93±3.91%位于视前区,76.27±4.88%位于下丘脑前部、结节部和乳头体区。视前区近一半的逆行标记神经元以及下丘脑前部、结节部和乳头体区超过三分之一的逆行标记神经元出现在内侧区域。对囊泡谷氨酸转运体2(VGLUT2)和谷氨酸脱羧酶65(GAD65)mRNA表达的分析显示,在逆行标记的下丘脑神经元的不同亚群中均有这两种氨基酸标记物,通常以谷氨酸能标记物VGLUT2占主导。即使在主要表达VGLUT2的下丘脑核团中,约十分之一的CTB免疫反应性(CTB-IR)神经元也是GAD65阳性。一些区域主要由含有GAD65 mRNA的逆行标记神经元组成。这些区域包括下丘脑外侧区的穹窿周部分,其中58.63±19.04%的CTB-IR神经元是GABA能的。这些结果表明,下丘脑的内侧和外侧核区都为VTA提供了大量输入。此外,共定位研究表明,这些投射不仅使用谷氨酸,还使用GABA进行神经传递。这些GABA能传入纤维可能构成重要的抑制机制,以微调VTA中特定信号的奖赏值。