Calretinin-immunoreactive local circuit neurons in area 17 of the cynomolgus monkey, Macaca fascicularis.
The connections of local circuit neurons immunoreactive for calcium-binding protein calretinin (CR-ir) were studied in area 17 of the macaque monkey visual cortex. Most CR-ir neurons were located in layers 2 and 3A. They were polymorphic and included bitufted, multipolar, pyramid-shaped neurons with smooth dendrites and Cajal-Retzius cells. The majority of CR-ir neurons were gamma-aminobutyric acid (GABA)-immunopositive (approximately 90%), and compromised about 14% of the total GABAergic neuron population. The axons of CR-ir cells had local arbors within layers 1-3, but the major trunks descended to deep layers 5 and 6 where they formed dense terminal fields within narrow columns (100-150 microns). This specific innervation of layers 5 and 6 appeared as a distinct feature of area 17 as it was not seen in the adjacent area 18. CR-ir boutons (n = 168) were GABA-ir (95%) and formed symmetric synapses. In layers 1-3, the majority of postsynaptic targets (n = 64) were GABAergic local circuit neurons [postsynaptic target distribution: GABA-positive dendrites (67%) and somata (14%), and GABA-negative dendrites (13%) and spines (6%)]. In deep layers, the most synapses (80%; n = 187) were formed with pyramidal cells where they provided a basket-type innervation [postsynaptic target distribution: GABA-positive dendrites (19%) and somata (1%), and GABA-negative dendrites (50%), spines (20%) and somata (10%)]. Unlike other GABAergic neurons, which innervate mainly pyramidal neurons, the CR-ir subpopulation only has pyramids as a preferred target in the deep layers (layers 5 and 6); however, in the superficial layers of the area 17, selectively form synapses mainly with other GABAergic cells. Thus, the CR-ir neurons appear to have a dual function of disinhibiting superficial layer neurons and inhibiting pyramidal output neurons in the deep layers.
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Institut für Neuroinformatik University of Zürich/ETH, Switzerland. virga@neuroinf.ethz.ch
D000818:Animals; D001369:Axons / Q000378:metabolism / Q000648:ultrastructure; D064032:Calbindin 2; D064026:Calbindins; D005260:Female; D007150:Immunohistochemistry; D008252:Macaca fascicularis; D008297:Male; D008854:Microscopy, Electron; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure; D010320:Parvalbumins / Q000378:metabolism; D017966:Pyramidal Cells / Q000502:physiology; D064030:S100 Calcium Binding Protein G / Q000378:metabolism*; D014793:Visual Cortex / Q000166:cytology* / Q000378:metabolism* / Q000648:ultrastructure; D014795:Visual Pathways / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D064032:Calbindin 2; D064026:Calbindins; D009419:Nerve Tissue Proteins; D010320:Parvalbumins; D064030:S100 Calcium Binding Protein G; D005680:gamma-Aminobutyric Acid