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Neurochemical Insights of Human Origins: A comparative analysis of dopaminergic axon innervation of the ventral striatum among primates

Hirter, Kristen Nicole
http://rave.ohiolink.edu/etdc/view?acc_num=kent156400567097679

Abstract Details

2019, MA, Kent State University, College of Arts and Sciences / Department of Anthropology.
What does it mean to be human? Some factors that come to mind are our intelligence, our ability to form and use language, and our complex emotional drives such as altruism and empathy. In anthropology, it has always been difficult to reconcile the evolution of these complex social behaviors through classical natural selection. Most studies on human brain evolution have focused on the cerebral cortex, the most expanded region in the brain compared to other species. However, the emergence of our lineage occurred much before any notable brain expansion in the fossil record. This suggests that the initial neurochemical changes that supported prosocial behavior and social monogamy, two factors crucial to the success of our clade, reside in an evolutionary older region of the brain. Now, new investigations focusing on the neurochemical profile of a region called the striatum are underway. Traditionally thought to only regulate motor control, the striatum is now known to play a large role in cognition, learning and memory, as well as modulate social behavior through relative neurotransmitter activity in the dorsal and ventral regions. A unique human neurochemical profile in the dorsal striatum suggests elevated dopamine and reduced acetylcholine in this area may have initiated prosocial behavior in early hominids that eventually gave way to the evolution of complex social traits in modern humans. To investigate the ventral striatum, we compared dopaminergic innervation in the region among 7 different species. The ventral striatum, mainly comprised of the nucleus accumbens, is heavily involved in the mesolimbic dopaminergic reward pathway and mediates reward salience and social behavior. It sends the majority of its projections to the ventral pallidum, which has also been included in the current study. The ventral pallidum mediates motor function in response to rewarding stimuli and is necessary for assigning the proper valence to reward. Our study sample included left hemisphere brain sections containing the ventral striatum and ventral pallidum from 42 individuals of the following species: Homo sapiens, Pan troglodytes, Pan paniscus, Macaca mulatta, Macaca nemestrina, Cebus apella, and Saguinus oedipus. We used immunohistochemical methods to stain for tyrosine hydroxylase (TH) and quantified TH-immunoreactive axon density using a stereological approach. We expected humans to have the greatest amount of innervation, and our results support this hypothesis. While the ultimate goal of this study is to determine uniquely human characteristics of the ventral striatum, we also expected differences among nonhuman primate species. Our predictions of S. oedipus and P. paniscus possessing increased dopaminergic innervation in the ventral striatum were not supported with our results, suggesting that affiliative and pair-bonding behavior is mediated by different mechanisms in nonhuman primate species. The implications of our findings our discussed in a larger evolutionary framework, and support the hypothesis that selection for a prosocial neurochemistry in the striatum of the earliest hominids facilitated the emergence of our species from the last common ancestor (LCA) we shared with the Pan clade.
Mary Ann Raghanti (Advisor)
Anthony Tosi (Committee Member)
Owen Lovejoy (Committee Member)
49 p.
Neurobiology
anthropology; human evolution; neurobiology; dopamine; striatum

Recommended Citations

Citations

  • Hirter, K. N. (2019). Neurochemical Insights of Human Origins: A comparative analysis of dopaminergic axon innervation of the ventral striatum among primates [Master's thesis, Kent State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=kent156400567097679

    APA Style (7th edition)

  • Hirter, Kristen. Neurochemical Insights of Human Origins: A comparative analysis of dopaminergic axon innervation of the ventral striatum among primates. 2019. Kent State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=kent156400567097679.

    MLA Style (8th edition)

  • Hirter, Kristen. "Neurochemical Insights of Human Origins: A comparative analysis of dopaminergic axon innervation of the ventral striatum among primates." Master's thesis, Kent State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=kent156400567097679

    Chicago Manual of Style (17th edition)

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This open access ETD is published by Kent State University and OhioLINK.