Pathways from auditory cortex to the cochlear nucleus in guinea pigs.
The inferior colliculus (IC) and superior olivary complex (SOC) are important sources of descending pathways to the cochlear nucleus. The IC and SOC are also targets of direct projections from the auditory cortex but it is not known if cortical axons contact the cells that project to the cochlear nucleus. Multi-labeling techniques were used to address this question in guinea pigs. A fluorescent anterograde tracer was injected into temporal cortex to label corticofugal axons. Different fluorescent tracers were injected into one or both cochlear nuclei to label olivary and collicular cells. The brain was subsequently processed for fluorescence microscopy and the IC and SOC were examined for apparent contacts between cortical axons and retrogradely labeled cells. The results suggest that cortical axons contact cochlear nucleus-projecting cells in both IC and SOC. In both regions, contacts were more numerous on the side ipsilateral to the injected cortex. In the IC, the contacted cells projected ipsilaterally or contralaterally to the CN. In the SOC, the contacted cells projected ipsilaterally, contralaterally or bilaterally to the CN. We conclude that auditory cortex is in a position to modulate descending pathways from both the IC and SOC to the cochlear nucleus.
Schofield
Brett R
BR
Department of Neurobiology, Northeastern Ohio Universities College of Medicine, 4209 State Route 44, P.O. Box 95, Rootstown, OH 44272, USA. bschofie@neoucom.edu
Coomes
Diana L
DL
D000818:Animals; D001303:Auditory Cortex / Q000033:anatomy & histology* / Q000502:physiology; D001306:Auditory Pathways / Q000033:anatomy & histology / Q000502:physiology; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D017626:Cochlear Nucleus / Q000033:anatomy & histology* / Q000502:physiology; D004525:Efferent Pathways / Q000033:anatomy & histology* / Q000502:physiology; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D007245:Inferior Colliculi / Q000033:anatomy & histology* / Q000502:physiology; D008856:Microscopy, Fluorescence; D009476:Neurons, Efferent / Q000502:physiology; D009847:Olivary Nucleus / Q000033:anatomy & histology* / Q000502:physiology
D005456:Fluorescent Dyes