Evidence for Ape and Human Specializations in Geniculostriate Projections from VGLUT2 Immunohistochemistry

• Type of Material: Article
• Authors: Katherine L. Bryant, Emory University; Carolyn Suwyn, Emory University; Katherine M. Reding, Emory University; John F. Smiley, Nathan Kline Institute; Troy A. Hackett, Vanderbilt University School of Medicine; Todd M Preuss, Emory University
• Language: English
• Date: 2012
• Publisher: Karger Publishers
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2012, Karger Publishers
• Final Published Version (URL): http://www.karger.com/Article/FullText/341135
• Title of Journal or Parent Work: Brain, Behavior and Evolution
• ISSN: 0006-8977
• Volume: 80
• Issue: 3
• Start Page: 210
• End Page: 221
• Grant/Funding Information: This study was supported by NIH/NIDCD (RO1 DC04318), the James S. McDonnell Foundation (JSMF 21002093), and the Yerkes National Primate Research Center and the Yerkes base grant (National Center for Research Resources P51RR165; Office of Research Infrastructure Programs/OD P51OD11132).
• Keywords: Blobs; Primate; Human; Chimpanzees; Vesicular glutamate transporter; Architectonics; Area 17; Evolution; Primary visual cortex
• Research Categories: Health Sciences, Pathology; Biology, Neuroscience

Abstract

Vesicular glutamate transporters reuptake glutamate into synaptic vesicles at excitatory synapses. Vesicular glutamate transporter 2 (VGLUT2) is localized in the cortical terminals of neuronal somas located in the main sensory nuclei of the thalamus. Thus, immunolabeling of cortex with antibodies to VGLUT2 can reveal geniculostriate terminal distributions in species in which connectivity cannot be studied with tract-tracing techniques, permitting broader comparative studies of cortical specializations. Here, we used VGLUT2 immunohistochemistry to compare the organization of geniculostriate afferents in primary visual cortex in hominid primates (humans, chimpanzees, orangutan), Old World monkeys (rhesus macaques, vervets), and New World monkeys (squirrel monkeys). The New World and Old World monkeys had a broad, dense band of terminal-like labeling in cortical layer 4C, a narrow band of labeling in layer 4A, and additional labeling in layers 2/3 and 6, consistent with results from conventional tract-tracing studies in these species. By contrast, although the hominid primates had a prominent layer 4C band, labeling of layer 4A was sparse or absent. Label was also present in layers 2/3 and 6, although labeling of layer 6 in hominids was weaker and possibly more individually variable than in Old World and New World monkeys. These findings are consistent with previous observations from cytochrome oxidase histochemistry and a very small number of connectivity studies, suggesting that the projection from the parvocellular layers of the lateral geniculate nucleus to layer 4A were strongly reduced or eliminated in humans and apes following their evolutionary divergence from the other anthropoid primates.