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Serotonergic innervation of the human amygdala and evolutionary implications
Author(s) -
Lew Caroline H.,
Hanson Kari L.,
Groeniger Kimberly M.,
Greiner Demi,
Cuevas Deion,
HrvojMihic Branka,
Schumann Cynthia M.,
Semendeferi Katerina
Publication year - 2019
Publication title -
american journal of physical anthropology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.146
H-Index - 119
eISSN - 1096-8644
pISSN - 0002-9483
DOI - 10.1002/ajpa.23896
Subject(s) - amygdala , serotonergic , neuroscience , extended amygdala , axon , basal ganglia , serotonin transporter , biology , serotonin , psychology , anatomy , central nervous system , stria terminalis , biochemistry , receptor
Objectives The serotonergic system is involved in the regulation of socio‐emotional behavior and heavily innervates the amygdala, a key structure of social brain circuitry. We quantified serotonergic axon density of the four major nuclei of the amygdala in humans, and examined our results in light of previously published data sets in chimpanzees and bonobos. Materials and methods Formalin‐fixed postmortem tissue sections of the amygdala from six humans were stained for serotonin transporter (SERT) utilizing immunohistochemistry. SERT‐immunoreactive (ir) axon fiber density in the lateral, basal, accessory basal, and central nuclei of the amygdala was quantified using unbiased stereology. Nonparametric statistical analyses were employed to examine differences in SERT‐ir axon density between amygdaloid nuclei within humans, as well as differences between humans and previously published data in chimpanzees and bonobos. Results Humans displayed a unique pattern of serotonergic innervation of the amygdala, and SERT‐ir axon density was significantly greater in the central nucleus compared to the lateral nucleus. SERT‐ir axon density was significantly greater in humans compared to chimpanzees in the basal, accessory basal, and central nuclei. SERT‐ir axon density was greater in humans compared to bonobos in the accessory basal and central nuclei. Conclusions The human pattern of SERT‐ir axon distribution in the amygdala complements the redistribution of neurons in the amygdala in human evolution. The present findings suggest that differential serotonergic modulation of cognitive and autonomic pathways in the amygdala in humans, bonobos, and chimpanzees may contribute to species‐level differences in social behavior.