Differential Pattern of Interhemispheric Connections Between Homotopic Layer V Regions in the Forelimb Representation in Rat Barrel Field Cortex.
Layer V neurons in forelimb and shoulder representations in rat first somatosensory cortex (SI) project to the contralateral SI. However, few studies have addressed whether projections from specific subregions of the forelimb representation, namely forepaw, wrist, or forearm, terminate at homotopic sites in the contralateral SI. Neuroanatomical retrograde (cholera toxin B subunit [CT-B]) or anterograde (biodextran amine [BDA]) tracers were injected into physiologically identified sites in layer V in specific forelimb and/or shoulder representations in SI to examine the projection to contralateral SI in young adult rats (N = 17). Injection and target sites were flattened and cut in a tangential plane to relate labeling to the body map or cut along a coronal plane to relate labeling to cortical layers. Results indicate that layer V neurons project to cortical laminae II-VI in contralateral SI, with the densest labeling in layer V followed by layer III. In contrast, layer V neurons send sparse projections to layer IV. Furthermore, layer V neurons in wrist, forearm, and shoulder project to homotopic sites in contralateral layer V, while neurons in the forepaw representation project largely to sites in perigranular and dysgranular cortex adjacent to their homotopic territory. Our results provide evidence for a differential pattern of interhemispheric projections from forelimb and shoulder representations to the opposite SI and a detailed description of areal and laminar projection patterns of layer V neurons in the SI forelimb and shoulder cortices.
Department of Biomedical Engineering, Herff College of Engineering, University of Memphis, Memphis, Tennessee.
Tina M
TM
Decosta-Fortune
Department of Biomedical Engineering, Herff College of Engineering, University of Memphis, Memphis, Tennessee.|Department of Anatomy and Neurobiology, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee.
Cheng X
CX
Li
Department of Biomedical Engineering, Herff College of Engineering, University of Memphis, Memphis, Tennessee.
Amy L
AL
de Jongh Curry
Department of Biomedical Engineering, Herff College of Engineering, University of Memphis, Memphis, Tennessee.|Department of Anatomy and Neurobiology, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee.
Robert S
RS
Waters
D000818:Animals; D002540:Cerebral Cortex / Q000166:cytology / Q000502:physiology*; D005260:Female; D005552:Forelimb / Q000166:cytology / Q000502:physiology*; D008297:Male; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D017966:Pyramidal Cells / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012782:Shoulder / Q000502:physiology*; D013003:Somatosensory Cortex / Q000166:cytology / Q000502:physiology*
barrel cortex; callosal projections; corticocortical connections; forepaw barrel subfield; somatosensory cortex