Projection to the inferior colliculus from the basal nucleus of the amygdala.

Projection to the inferior colliculus from the basal nucleus of the amygdala.

Marsh Robert A; Fuzessery Zoltan M; Grose Carol D; Wenstrup Jeffrey J

The Journal of neuroscience : the official journal of the Society for Neuroscience

2002

2002-12

This report describes a projection from the amygdala, a forebrain center mediating emotional expression, to the inferior colliculus (IC), the midbrain integration center of the ascending auditory system. In the IC of mustached bats (Pteronotus parnellii) and pallid bats (Antrozous pallidus), we placed deposits of retrograde tracers at physiologically defined sites and then searched for retrogradely labeled somata in the forebrain. Labeling was most sensitive in experiments using cholera toxin B-subunit as tracer. We consistently observed retrograde labeling in a single amygdalar subdivision, the magnocellular subdivision of the basal nucleus (Bmg). The Bmg is distinctive across mammals, containing the largest cells in the amygdala and the most intense acetylcholinesterase staining. Labeled amygdalar cells occurred ipsilateral and contralateral to IC deposits, but ipsilateral labeling was greater, averaging 72%. Amygdalar labeling was observed after tracer deposits throughout the IC, including its central nucleus (ICC). In comparison, labeling in the auditory cortex (layer V) was heavily ipsilateral (averaging 92%). Cortical labeling depended on the location of IC deposits: dorsomedial deposits resulted in the most labeled cells, whereas ventrolateral deposits labeled few or no cortical cells. Cortical labeling occurred after several deposits in the ICC. Across experiments, the average number of labeled cells in the amygdala was similar to that in the auditory cortex, indicating that the amygdalocollicular projection is significant. The results demonstrate a direct, widespread projection from the basal amygdala to the IC. They also suggest the presence of a rapid thalamoamygdalocollicular feedback circuit that may impose emotional content onto processing of sensory stimuli at a relatively low level of an ascending sensory pathway.

Animals; Acoustic Stimulation/methods; Species Specificity; Action Potentials/physiology; Amygdala/*cytology/physiology; Dextrans; Rhodamines; Fluorescent Dyes; *Stilbamidines; Auditory Cortex/cytology; Auditory Pathways/*cytology/physiology; Axonal Transport/physiology; Brain Stem/cytology; Chiroptera/*anatomy & histology/physiology; Cholera Toxin/pharmacokinetics; Inferior Colliculi/*cytology/physiology; Neurons/cytology/physiology; Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; Electrodes; Implanted

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10449–10460

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