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The lateral bed nucleus of the stria terminalis (BSTL) is involved in mediating anxiety-related behaviors to sustained aversive stimuli. The BSTL forms part of the central extended amygdala, a continuum composed of the BSTL, the amygdala central nucleus, and cell columns running between the two. The central subdivision (BSTLcn) and the juxtacapsular subdivision (BSTLJ) are two BSTL regions that lie above the anterior commissure, near the ventral striatum. The amygdala, a heterogeneous structure that encodes emotional salience, projects to both the BSTL and ventral striatum. We placed small injections of retrograde tracers into the BSTL, focusing on the BSTLcn and BSTLJ, and analyzed the distribution of labeled cells in amygdala subregions. We compared this to the pattern of labeled cells following injections into the ventral striatum. All retrograde results were confirmed by anterograde studies. We found that the BSTLcn receives stronger amygdala inputs relative to the BSTLJ. Furthermore, the BSTLcn is defined by inputs from the corticoamygdaloid transition area and central nucleus, while the BSTLJ receives inputs mainly from the magnocellular accessory basal and basal nucleus. In the ventral striatum, the dorsomedial shell receives inputs that are similar, but not identical, to inputs to the BSTLcn. In contrast, amygdala projections to the ventral shell/core are similar to projections to the BSTLJ. These findings indicate that the BSTLcn and BSTLJ receive distinct amygdala afferent inputs and that the dorsomedial shell is a transition zone with the BSTLcn, while the ventral shell/core are transition zones with the BSTLJ., (© 2013 Wiley Periodicals, Inc.)

The ventral striatum mediates goal-directed behaviors based, in part, on inputs from the amygdala. However, striatal areas caudal to the ventral striatum also receive inputs from the amygdala. In primates, the amygdala projects to the central ventral putamen, lateral amygdalostriatal area, and caudal ventral putamen, suggesting that these regions are also "limbic-related." The anterior insula, which integrates sensory and amygdaloid inputs, projects to the classic ventral striatum. We used retrograde and anterograde tract tracing techniques to determine the extent to which specific subdivisions of the insula influence the caudal ventral striatum in the primate. The anterior (agranular and rostral dysgranular) insula has significant inputs to caudal ventral striatal regions that receive projections from the amygdala. In contrast, the posterior (granular) insula has sparse projections. Within the agranular insula, the posteromedial agranular (Iapm), lateral agranular (Ial), and posterolateral agranular (Iapl) subdivisions have the strongest inputs. These subdivisions mediate olfactory, gustatory, and visceral information processing (Carmichael and Price JL [1996b] J. Comp. Neurol. 363:642-640). In contrast, the intermediate agranular subdivision (Iai) is relatively devoid of visceral/gustatory inputs and has few inputs. In summary, caudal ventral striatal areas that receive amygdaloid inputs also receive significant innervation by agranular and dysgranular insula subdivisions that are themselves connected with the amygdala. Within this projection, the Ial, Iapm, and Iapl make the strongest contribution, suggesting that highly processed visceral/autonomic information, taste, and olfaction influence behavioral responses mediated by the caudal ventral striatum., ((c) 2005 Wiley-Liss, Inc.)

The ventral striatum mediates goal-directed behavior through limbic afferents. One well-established afferent to the ventral striatum is the amygdaloid complex, which projects throughout the shell and core of the nucleus accumbens, the rostral ventromedial caudate nucleus, and rostral ventromedial putamen. However, striatal regions caudal to the anterior commissure also receive inputs from the amygdala. These caudal areas contain histochemical and cytoarchitectural features that resemble the shell and core, based on our recent studies. Specifically, there is a calcium binding protein (CaBP)-poor region in the lateral amygdalostriatal area that resembles the "shell." To examine the idea that the caudal ventral striatum is part of the "classic" ventral striatum, we placed small injections of retrograde tracers throughout the caudal ventral striatum/amygdalostriatal area and charted the distribution of specific amygdaloid inputs. Amygdaloid inputs to the CaBP-poor zone in the lateral amygdalostriatal area arise from the basal nucleus, the magnocellular subdivision of the accessory basal nucleus, the periamygdaloid cortex, and the medial subdivision of the central nucleus, resembling that of the shell of the ventral striatum found in our previous studies. There are also amygdaloid inputs to CaBP-positive areas outside the shell, which originate mainly in the basal nucleus. Taken together, the "limbic-related" striatum forms a continuum from the rostral ventral striatum through the caudal ventral striatum/lateral amygdalostriatal area based on histochemical and cellular similarities, as well as inputs from the amygdala.