title: Differences in cortical serotonergic innervation among humans, chimpanzees, and macaque monkeys: a comparative study.
abstract: In this study, we assess the possibility that the evolution of human intellectual capacities was supported by changes in the supply of serotonin to the frontal cortex. To this end, quantitative comparative analyses were performed among humans, chimpanzees, and macaques. Immunohistochemical methods were used to visualize serotonin transporter-immunoreactive (SERT-ir) axons within the cerebral cortex. Areas 9 and 32 were chosen for evaluation due to their roles in working memory and theory of mind, respectively. Primary motor cortex was also evaluated because it is not associated with higher cognitive functions. The findings revealed that humans do not display a quantitative increase in serotonin innervation. However, the results indicated region- and layer-specific differences among species in serotonergic innervation pattern. Compared with macaques, humans and chimpanzees together displayed a greater density of SERT-ir axons relative to neuron density in layers V/VI. This change was detected in cortical areas 9 and 32, but not in primary motor cortex. Further, morphological specializations, coils of axons, were observed in humans and chimpanzees that were absent in macaques. These features may represent a greater capacity for cortical plasticity exclusive to hominoids. Taken together, these results indicate a significant reorganization of cortical serotonergic transmission in humans and chimpanzees.
authors.affiliation: Department of Anthropology and School of Biomedical Sciences, Kent State University, Kent, OH 44242, USA. mraghant@kent.edu
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Raghanti
authors.forename: Cheryl D
authors.initials: CD
authors.lastname: Stimpson
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Marcinkiewicz
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Erwin
authors.forename: Patrick R
authors.initials: PR
authors.lastname: Hof
authors.forename: Chet C
authors.initials: CC
authors.lastname: Sherwood
mesh_terms: D000328:Adult; D000818:Animals; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D002540:Cerebral Cortex / Q000166:cytology* / Q000502:physiology*; D005260:Female; D000882:Haplorhini; D006801:Humans; D008251:Macaca; D008297:Male; D008875:Middle Aged; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000502:physiology; D002679:Pan troglodytes; D012701:Serotonin / Q000502:physiology*; D013045:Species Specificity
chemical_list: D012701:Serotonin