The Journal of Neuroscience, December 1, 2002, 22(23):10449-10460
Projection to the Inferior Colliculus from the Basal Nucleus
of the Amygdala
Robert A.
Marsh1,
Zoltan M.
Fuzessery2,
Carol
D.
Grose1, and
Jeffrey J.
Wenstrup1
1 Department of Neurobiology and Pharmacology,
Northeastern Ohio Universities College of Medicine, Rootstown, Ohio
44272, and 2 Department of Zoology and Physiology,
University of Wyoming, Laramie, Wyoming 82071
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.
Key words:
amygdala; auditory pathways; auditory cortex; bat; chiroptera; cholera toxin; emotion; inferior colliculus
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