Amygdala projections to the lateral bed nucleus of the stria terminalis in the macaque: comparison with ventral striatal afferents

Abstract

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.

Keywords: amygdalopiriform transition area; anxiety; corticoamygdaloid transition region; dorsomedial shell; extended amygdala; juxtacapsular; oval.

Figure 1

Adjacent sections through the BST processed for AChE (panels A–C), ENK (panels D–F), ST (panels G–I), and NT (panels (J–L). Sections are arranged in rostral to caudal order from left to right. Scale bar = 1mm.

Figure 2

Coronal sections through the rostral to caudal primate amygdala stained using cresyl violet (A–D), with adjacent sections processed for AChE activity (E–H). Scale bar = 2.5 mm. (I) Higher power photomicrograph of the primate CTA, at the level of panel C (boxed area). The asterisk is centered on the CTA, which is situated in the semiannual sulcus (arrowhead) between the tri-laminar PAC and the six-layered entorhinal cortex. Scale bar = 1mm.

Figure 3

(A) Schematics and representative photomicrographs of retrograde injections into the BSTL. Injections were classified as centered mainly in the BSTLcn (light gray; J24FS, J28LY, J29WGA, J28WGA) or the BSTLJ (dark gray; J28FR, J28FS, J29FR). Representative injections sites are shown with adjacent sections processed for AChE to delineate boundaries of the BSTLDcn (case J28WGA) and BSTLJ (case J28LY), respectively. (B) Schematics of injections into subregions of the ventral striatum including the dorsomedial shell (light gray; J24WGA), ventral shell (dark gray; J27FS, J26FS, J27FR), core (black; J13WGA), and the centromedial and ventromedial caudate nucleus (white; J25FS, J24FR). Photomicrographs of several representative injections are shown. Scale bars = 2 mm.

Figure 4

Charts of retrogradely labeled cells through the rostrocaudal amygdala (left to right) following tracer injections in the BSTLcn (case J29WGA) (A) and the BSTLJ (J28FS) (B), arranged in rostrocaudal order. 1 dot represents 1 cell.

Figure 5

Photomicrographs of retrogradely labeled cells in the amygdala following injections in the BSTLcn (A–B, D–E) or BSTLJ (G–H). (A–B) Low and high power photomicrographs of labeled cells in the CeLcn (level shown in C) following injection centered on the BSTLcn. (D–E) Photomicrographs of labeled cells in the medial Bpc/CTA (level shown in F) after the same injection. (G–H) Image of labeled cells in the ABmc resulting from an injection centered on the BSTLJ (level in I). Scale bars = 50 μm.

Figure 6

Charts of retrogradely labeled cells through the rostrocaudal amygdala (left to right) following tracer injections in the dorsomedial shell (J24WGA) (A) and the ventral shell (J27FS) (B). 1 dot represents 1 cell.

Figure 7

Schematic of anterograde injection sites in the amygdala at mid- (A) and caudal (B) levels. Pink= accessory basal nucleus; green= basal nucleus (asterisk denotes inclusion of CTA); blue=lateral nucleus; yellow= central nucleus; orange= medial nucleus; purple = amygdalohippocampal area/ABs. See text for details of placement.

Figure 8

Distribution of anterogradely labeled fibers in the BSTL (A–C) and shell (D) following an injection in the Bmc (J12FR). (C) Darkfield photomicrograph of the boxed area in (B) showing labeled fibers in the BSTLJ, BSTLP and SLEAc, with an absence of fibers in the BSTLcn. Asterisk indicates passing fibers, and dotted oval indicates boundary of the BSTLcn. Scale bar = 2mm.

Figure 9

Distribution of anterogradely labeled fibers in the BSTL (A–C), core and shell (D), following an injection in rostral medial Bpc/CTA (J20LY). (C) Darkfield photomicrograph of the boxed area in (B) showing labeled fibers in the BSTL subdivisions and SLEAc. Asterisks indicate passing fibers and dotted oval indicates boundaries of the BSTLDcn. Scale bar = 2mm.

Figure 10

Distribution of anterogradely labeled fibers in the BSTL (A–C) and shell following an injection in the ABmc (J8LY). (C) Darkfield photomicrograph of the boxed area in (B) showing labeled fibers in the BSTLJ, BSTLP and SLEAc, with an absence of fibers in the BSTLcn. Asterisk indicates passing fibers and dotted oval indicates boundaries of the BSTLDcn. Scale bar = 2mm.

Figure 11

Distribution of anterogradely labeled fibers following injections in the CeM and the CeLcn. (A–D) Anterogradely labeled fibers in the shell (A) and BSTL subdivisions (B–C) following an injection centered in the CeM. (D) Darkfield photomicrograph of the boxed area in (C) showing labeled fibers in the BSTLcn, BSTLP, BSTLJ and SLEAc. (E–H) Distribution of anterogradely labeled fibers in the BSTL subdivisions (E–G) following an injection in the CeLcn (J9FS). (H) Darkfield photomicrograph of the boxed area in (G), showing fibers in the BSTLcn and SLEAc.

Figure 12

Composite charts of retrogradely labeled cells resulting from injections centered on the BSTL and ventral striatal subregions. (A–B) Injections centered in the BSTLcn (green) and BSTLJ (magenta) result in differential distributions of retrogradely labeled cells in amygdala subregions. (C–D) Injections into specific subregions of the ventral striatum also result in differential distributions of labeled cells in the amygdala subregions. Dorsomedial shell (green); ventral shell (magenta); core (light pink); ventromedial caudate nucleus (black). Comparisons across BSTL and ventral striatal cases shows that the distribution following BSTLcn injections is most similar to that following an injection into the dorsomedial shell (green), while injections in the BSTLJ (magenta) result in a pattern of labeled cells that is similar to that of the ventral shell (magenta) and core (light pink).