Evidence for ape and human specializations in geniculostriate projections from VGLUT2 immunohistochemistry.
Vesicular glutamate transporters (VGLUTs) reuptake glutamate into synaptic vesicles at excitatory synapses. 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, and an orangutan), Old World monkeys (rhesus macaques and vervets), and New World monkeys (squirrel monkeys). The New 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. Labeling was also present in layers 2/3 and 6, although labeling of layer 6 was weaker in hominids and possibly more individually variable than in Old 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 projections 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.
Division of Neuropharmacology and Neurologic Diseases, Yerkes National Primate Research Center, Emory University, Atlanta, GA 30329 USA.
Katherine L
KL
Bryant
Carolyn
C
Suwyn
Katherine M
KM
Reding
John F
JF
Smiley
Troy A
TA
Hackett
Todd M
TM
Preuss
D000344:Afferent Pathways / Q000737:chemistry* / Q000502:physiology; D000368:Aged; D000818:Animals; D005075:Biological Evolution; D015415:Biomarkers; D005260:Female; D005829:Geniculate Bodies / Q000033:anatomy & histology* / Q000737:chemistry; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D009419:Nerve Tissue Proteins / Q000032:analysis*; D010802:Phylogeny; D011323:Primates / Q000033:anatomy & histology* / Q000145:classification / Q000378:metabolism; D013045:Species Specificity; D050599:Vesicular Glutamate Transport Protein 2 / Q000032:analysis*; D014793:Visual Cortex / Q000033:anatomy & histology* / Q000737:chemistry
D015415:Biomarkers; D009419:Nerve Tissue Proteins; C493476:SLC17A6 protein, human; D050599:Vesicular Glutamate Transport Protein 2