title: Evidence for layer-specific differences in auditory corticocollicular neurons.
abstract: Recent data suggest that there may be distinct processing streams emanating from auditory cortical layers 5 and 6 that influence the auditory midbrain. To determine whether these projections have different physiological properties, we injected rhodamine-tagged latex tracer beads into the inferior colliculus of >30-day-old mice to label these corticofugal cells. Whole-cell recordings were performed on 62 labeled cells to determine their basic electrophysiological properties and cells were filled with biocytin to determine their morphological characteristics. Layer 5 auditory corticocollicular cells have prominent I(h)-mediated sag and rebound currents, have relatively sluggish time constants, and can generate calcium-dependent rhythmic bursts. In contrast, layer 6 auditory corticocollicular cells are non-bursting, do not demonstrate sag or rebound currents and have short time constants. Quantitative analysis of morphology showed that layer 6 cells are smaller, have a horizontal orientation, and have very long dendrites (>500 μm) that branch profusely both near the soma distally near the pia. Layer 5 corticocollicular cells are large pyramidal cells with a long apical dendrite with most branching near the pial surface. The marked differences in physiological properties and dendritic arborization between neurons in layers 5 and 6 make it likely that each type plays a distinct role in controlling auditory information processing in the midbrain.
authors.affiliation: Neuroscience Program, University of Illinois at Urbana-Champaign, United States.
authors.forename: B J
authors.initials: BJ
authors.lastname: Slater
authors.forename: A M
authors.initials: AM
authors.lastname: Willis
authors.forename: D A
authors.initials: DA
authors.lastname: Llano
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001303:Auditory Cortex / Q000166:cytology* / Q000502:physiology; D001306:Auditory Pathways / Q000502:physiology*; D001369:Axons / Q000502:physiology; D048430:Cell Shape / Q000502:physiology; D003712:Dendrites / Q000502:physiology*; D007245:Inferior Colliculi / Q000166:cytology* / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009474:Neurons / Q000166:cytology* / Q000502:physiology; D018408:Patch-Clamp Techniques