Evidence for layer-specific differences in auditory corticocollicular neurons

Abstract

Recent data suggest that there may be distinct processing streams emanating from auditory cortical layer 5 and layer 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 Ihmediated 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 layer 5 and layer 6 make it likely that each type plays a distinct role in controlling auditory information processing in the midbrain.

High-throughput mapping of long-range neuronal projection using in situ sequencing

“…We identified no IT subclass restricted to L2/3, and only a small fraction of IT neurons (45 out of 805, 6%) were found in L5 or L6 enriched subclasses (Leaf 43, 19, and 45). Similarly, we identified no PT subclass specific to L5 or L6, in contrast to previous reports of layer-specific PT classes defined by morphological and electrophysiological properties 20 (Supp. Note 7; Supp Fig.…”

Cell-Specific Activity-Dependent Fractionation of Layer 2/3→5B Excitatory Signaling in Mouse Auditory Cortex

“…The skull was exposed to blue light (LED light: peak wavelength ϭ 461.4 nm; FWHM ϭ 19.3 nm; M470L3; Thorlabs) for 10 s; 1 s acoustic stimuli were presented 3 s after initiation of exposure to blue light. During this time the endogenous FA signal (540 nm) was recorded by a CCD camera (Middleton et al, 2011). Two regions of sound-evoked FA activity were consistently observed: The more caudal of the two regions corresponds to the primary auditory cortex (A1) and the more rostral one corresponds to the anterior auditory field (AAF; Fig.…”

“…For morphological reconstructions, the angle of cutting was slightly modified for optimal preservation of dendritic arbors. Dendrites were three-dimensionally traced in stitched image stacks (Neurolucida) and datasets were further analyzed to quantify dendritic length as previously described (Shepherd et al, 2005;Yamawaki et al, 2014).…”

“…1D3; Takahashi et al, 2006). FA signals are generated by mitochondrial flavoproteins due to changes in oxidation state caused by neuronal activity (Shibuki et al, 2003;Middleton et al, 2011). Mirror-reversed tonotopic gradients have been used to identify A1 and the AAFs in many mammalian species including mice (Kaas, 2011;Guo et al, 2012).…”

“…1H ) between the centers of two regions of the FA signals are consistent with localization of mouse A1 using FA, electrophysiological recordings, or optical Ca 2ϩ imaging (Stiebler et al, 1997;Takahashi et al, 2006;Guo et al, 2012;Honma et al, 2013;Issa et al, 2014). After completion of FA-assisted localization of A1, we applied a fluorescent dye to mark the location of A1 (Lefort et al, 2009), enabling us to precisely localize the A1 region of AC in subsequently prepared brain slices (Fig. 1D).…”