Topographic organization of neurons in the acoustic thalamus that project to the amygdala

TLDR

Posterior thalamic projections to the amygdala are implicated in processing the emotional significance of acoustic stimuli. The study aimed to identify which amygdalar nuclei receive inputs from posterior thalamic regions that themselves receive inferior colliculus afferents. Rats were examined with anterograde and retrograde axonal transport methods to map posterior thalamic projections to the amygdala and striatum. WGA‑HRP injections into posterior thalamic nuclei (MGM, PIN, POM) produced anterograde labeling of the lateral, central, medial, and basomedial amygdalar nuclei, the amygdalostriatal transition area, and posterior caudate putamen, while retrograde tracing showed that AL and AST receive inputs from MGM, PIN, and SG (and LP), whereas ACE, AM, and ABM receive inputs only from POM, demonstrating that AL and AST are linked to thalamic regions that receive inferior colliculus afferents.

Abstract

Projections from the posterior thalamus to the amygdala have been implicated in the processing of the emotional significance of acoustic stimuli. The aim of the present studies was to determine which areas of the amygdala receive afferents from posterior thalamic structures that, in turn, receive afferents (presumably acoustic afferents) from the inferior colliculus. Projections from the posterior thalamus to the amygdala and striatum were examined in rats using anterograde and retrograde axonal transport techniques. Following injections of WGA-HRP into the posterior thalamic areas [including the medial division of the medial geniculate body, the posterior intralaminar nucleus (PIN) and the medial posterior complex (POM)], anterograde transport was seen in the lateral (AL), central (ACE), medial (AM), and basomedial (ABM) nuclei of the amygdala and in the amygdalostriatal transition area (AST) and posterior caudate putamen (CPU). Injection of WGA-HRP into each anterogradely labeled area produced retrograde transport to the posterior thalamus, but the pattern of transport varied with the site of the injection. Injections in AL and AST produced retrograde transport to neurons in the medial division of the medial geniculate body (MGM), PIN, suprageniculate nucleus (SG) and, to a lesser extent, the lateral posterior nucleus (LP). Injections of the ACE, AM, and ABM, in contrast, only labeled cells in POM. While the MGM, PIN, and SG each receive afferents from the inferior colliculus, POM does not. AL and AST, therefore, receive inputs from thalamic areas that, in turn, receive inputs from the inferior colliculus.