Differences in intrinsic properties and local network connectivity of identified layer 5 and layer 6 adult mouse auditory corticothalamic neurons support a dual corticothalamic projection hypothesis.
Intrinsic properties, morphology, and local network circuitry of identified layer 5 and layer 6 auditory corticothalamic neurons were compared. We injected fluorescent microspheres into the mouse auditory thalamus to prelabel corticothalamic neurons, then recorded and filled labeled layer 5 or layer 6 auditory cortical neurons in vitro. We observed low-threshold bursting in adult, but not juvenile, layer 5 corticothalamic neurons that was voltage and time dependent with nonlinear input-output properties, whereas adult layer 6 corticothalamic neurons demonstrated a regular spiking. Layer 5 corticothalamic neurons had larger somata, thicker apical dendrites and were more likely to have a layer 1 apical dendrite than layer 6 neurons. Using laser photostimulation, identified layer 5 corticothalamic neurons received excitatory input from a wide area of layers 2/3, 4, and 5 with widespread gamma-aminobutyric acidergic input from layer 2/3 and lower layer 5, whereas layer 6 corticothalamic neurons from the same cortical column received circumscribed excitatory input and discrete patches of inhibition derived from layer 6 of adjacent columns. These data demonstrate that layer 5 and layer 6 corticothalamic neurons receive unique sets of inputs and process them in different manners, supporting the hypothesis that layer-specific corticothalamic projections play distinct roles in information processing.
Department of Neurology, University of Chicago, Chicago, IL 60637, USA. a.daniel.llano@gmail.com
Daniel A
DA
Llano
S Murray
SM
Sherman
D000818:Animals; D001303:Auditory Cortex / Q000166:cytology / Q000502:physiology*; D005260:Female; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008953:Models, Anatomic; D008959:Models, Neurological; D009415:Nerve Net / Q000166:cytology* / Q000502:physiology*; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D011984:Sensory Receptor Cells / Q000166:cytology* / Q000502:physiology*; D013788:Thalamus / Q000166:cytology* / Q000502:physiology*