Foster E F, Mehta R P, Bottjer S W
Department of Biology, University of Southern California, Los Angeles 90089-2520, USA.
J Comp Neurol. 1997 Jun 9;382(3):364-81. doi: 10.1002/cne.903820305.
The medial magnocellular nucleus of the anterior neostriatum (mMAN) is a small cortical nucleus which was previously identified as a component of the neural circuitry controlling vocal behavior in songbirds based on its efferent connection to the High Vocal Center (HVC), a major song control nucleus (Nottebohm et al. [1982] J. Comp. Neurol. 207:344-357; Bottjer et al. [1989] J. Comp. Neurol. 279:312-326). We have conducted tract tracing experiments (using wheat-germ agglutinin-horseradish peroxidase (WGA-HRP), the carbocyanine dye DiI, and biocytin) to determine the complete pattern of afferent and efferent connections of mMAN in adult male zebra finches. We confirmed the existence of an efferent projection from mMAN to HVC and discovered a novel projection to the region medial to caudal HVC called paraHVC (pHVC). Injections of retrograde tracers into mMAN showed that afferent input to mMAN originates from the dorsomedial nucleus of the posterior thalamus (DMP). Injections of DiI into DMP produced anterograde label over mMAN, thus confirming the DMP-to-mMAN projection. Interestingly, this anterograde label extended beyond the region of mMAN defined by HVC-projecting neurons into the immediately surrounding cortex. This extended terminal field of DMP efferents indicates that mMAN encompasses a core population of projection neurons surrounded by a shell of non-HVC-projecting neurons, both of which receive input from the dorsal thalamus. Analysis of retrograde DiI label resulting from DMP injections revealed two major sources of afferent input to DMP originating in regions of the archistriatum and hypothalamus. Inputs to DMP were distributed throughout the dorsal archistriatum and included the area that receives a projection from the parvicellular shell region of the lateral magnocellular nucleus of the anterior neostriatum, a song control nucleus, as well as the dorsal portion of the robust nucleus of the archistriatum, the motor-cortical output of the song control system. The projections from song control regions of the archistriatum to DMP may feed information back into telencephalic song control circuitry via the DMP-->mMAN-->HVC/pHVC pathway. The other source of afferent input to DMP is located in the external cellular stratum of the lateral hypothalamus (SCE). This newly delineated SCE-->DMP-->mMAN-->HVC/pHVC pathway is the first report of a hypothalamic brain region neuroanatomically integrated with song control circuitry. Because hypothalamic brain regions are important for homeostasis and regulating behavior, the trans-synaptic circuitry of mMAN may help to integrate information about the bird's internal state, such as sexual maturation, with song learning and production.
新纹状体前部内侧大细胞核（mMAN）是一个小的皮质核团，基于其与高级发声中枢（HVC，一个主要的发声控制核团）的传出连接，它先前被确定为控制鸣禽发声行为的神经回路的一个组成部分（诺特博姆等人[1982年]《比较神经学杂志》207:344 - 357；博捷尔等人[1989年]《比较神经学杂志》279:312 - 326）。我们进行了示踪实验（使用小麦胚芽凝集素 - 辣根过氧化物酶（WGA - HRP）、羰花青染料DiI和生物素）来确定成年雄性斑胸草雀中mMAN传入和传出连接的完整模式。我们证实了从mMAN到HVC存在传出投射，并发现了一个到HVC尾侧内侧区域称为副HVC（pHVC）的新投射。向mMAN注射逆行示踪剂表明，mMAN的传入输入起源于丘脑后部背内侧核（DMP）。向DMP注射DiI在mMAN上产生顺行标记，从而证实了从DMP到mMAN的投射。有趣的是，这种顺行标记延伸到了由投射到HVC的神经元所定义的mMAN区域之外，进入了紧邻的周围皮质区域。DMP传出纤维的这种延伸的终末场表明，mMAN包含一群核心的投射神经元，其周围是一层不投射到HVC的神经元，两者都从背侧丘脑接收输入。对DMP注射产生的逆行DiI标记的分析揭示了起源于古纹状体和下丘脑区域的DMP传入输入的两个主要来源。DMP的输入分布在整个背侧古纹状体，包括接受来自新纹状体前部外侧大细胞核小细胞壳区域（一个发声控制核团）投射的区域，以及古纹状体粗壮核的背侧部分，即发声控制系统的运动皮质输出。从古纹状体的发声控制区域到DMP的投射可能通过DMP→mMAN→HVC/pHVC通路将信息反馈到端脑发声控制回路中。DMP的另一个传入输入来源位于下丘脑外侧的细胞外层（SCE）。这条新描绘的SCE→DMP→mMAN→HVC/pHVC通路是下丘脑脑区在神经解剖学上与发声控制回路整合的首次报道。由于下丘脑脑区对体内平衡和调节行为很重要，mMAN的跨突触回路可能有助于整合有关鸟类内部状态（如性成熟）的信息与发声学习和发声产生。
