Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, Columbia, SC 29208, USA.
Neuroscience. 2012 Mar 15;205:112-24. doi: 10.1016/j.neuroscience.2011.12.036. Epub 2012 Jan 5.
The projections of the infralimbic area (IL) of the medial prefrontal cortex to the intercalated nuclei (ICNs) of the amygdala are thought to form a critical component of the forebrain circuitry for fear extinction. Despite the importance of these projections, there have been no focussed anatomical studies that have investigated the extent of IL inputs to different portions of the ICN complex. The present investigation used anterograde tract tracing in the rat to study the projections of the ventromedial PFC, including the IL, to the ICNs and surrounding amygdalar regions. Immunohistochemistry for the μ-opioid receptor (MOR) was used to identify the ICNs. At rostral levels of the amygdala there was a very dense projection to a far lateral portion of the capsular subdivision of the central nucleus (CLC) located between the main and medial ICNs, but only very light projections to these ICNs and the lateral ICNs. This distinct portion of the CLC receiving strong IL inputs was termed the capsular infralimbic target zone (CITZ), and was MOR-negative. Likewise, at more caudal levels of the amygdala, IL projections to the medial, lateral, and dorsal ICNs were light to moderate compared with projections to adjacent portions of the basolateral amygdala and amygdalostriatal transitional area. These findings suggest that the putative role of the IL-to-ICN connection in fear inhibition may be mediated by light to moderate projections from the IL to the medial ICN, and that the CITZ may be an equally important amygdalar target for this function.
脑岛皮质下区（ICN）的内侧前额叶皮质的投射被认为是恐惧消退的大脑前回路的关键组成部分。尽管这些投射非常重要，但目前还没有专门的解剖学研究来调查 IL 输入到 ICN 复合体不同部位的程度。本研究采用逆行追踪在大鼠中研究了腹侧前额叶皮质（包括 IL）向 ICN 和周围杏仁核区域的投射。使用 μ 阿片受体（MOR）免疫组织化学来识别 ICN。在杏仁核的前侧水平，有一个非常密集的投射到中央核（CLC）的胶囊亚区的一个非常外侧的部分，位于主要和内侧 ICN 之间，但对这些 ICN 和外侧 ICN 的投射非常轻。这个接收强烈 IL 输入的 CLC 明显部分被称为胶囊内 IL 目标区（CITZ），并且是 MOR 阴性的。同样，在杏仁核的更后侧水平，IL 对内侧、外侧和背侧 ICN 的投射与对相邻的外侧杏仁核和杏仁核纹状体过渡区的投射相比，是轻到中度的。这些发现表明，IL 到 ICN 的连接在恐惧抑制中的潜在作用可能是由 IL 到内侧 ICN 的轻到中度投射介导的，而 CITZ 可能是该功能的一个同样重要的杏仁核靶区。
