Periodic Organization of a Major Subtype of Pyramidal Neurons in Neocortical Layer V

Abstract

A major question in neocortical research is the extent to which neuronal organization is stereotyped. Previous studies have revealed functional clustering and neuronal interactions among cortical neurons located within tens of micrometers in the tangential orientation (orientation parallel to the pial surface). In the tangential orientation at this scale, however, it is unknown whether the distribution of neuronal subtypes is random or has any stereotypy. We found that the tangential arrangement of subcerebral projection neurons, which are a major pyramidal neuron subtype in mouse layer V, was not random but significantly periodic. This periodicity, which was observed in multiple cortical areas, had a typical wavelength of 30 m. Under specific visual stimulation, neurons in single repeating units exhibited strongly correlated c-Fos expression. Therefore, subcerebral projection neurons have a periodic arrangement, and neuronal activity leading to c-Fos expression is similar among neurons in the same repeating units. These results suggest that the neocortex has a periodic functional micro-organization composed of a major neuronal subtype in layer V.

Mixed functional microarchitectures for orientation selectivity in the mouse primary visual cortex

“…These results indicate that similarly tuned cells tend to cluster along the vertical direction (∼60 μm within 100 μm length) of a minicolumn. Our results may suggest that functional minicolumns are vertically short units restricted in a single layer21. However, due to the very posterior location of V1, minicolumns are not perfectly straight, but slightly curved.…”

The polycomb component Ring1B regulates the timed termination of subcerebral projection neuron production during mouse neocortical development

“…To this end, we performed retrograde labeling of neurons that extend their axonal terminals into the pons by injecting Alexa Fluor 555-conjugated cholera toxin B subunit (CTB555) into the pons. When CTB555 was injected into the pons at P1, a part of layer V CTIP2 ++ neurons were labeled in a retrograde manner in the S1 area of control mice at P2 as previously described, both in control and in Ring1B-deficient mice (Maruoka et al, 2011) (Fig. 3H-O).…”

Neuronal subtype specification in establishing mammalian neocortical circuits

“…Although layer V neurons are mostly subcerebral projection neurons (SCPNs), it is notable that approximately 20% of neocortical CPNs localize in layer V, and these neurons are similar to layers II/III CPNs in their molecular expression and connectivity (Molyneaux et al, 2009). Notably, layer V contains large pyramidal neurons that are disposed in radial clusters; these neurons express specific subsets of genes such as Ctip2 and Id2, and are segregated from CPNs that occupy the same layer (Kwan et al, 2012;Maruoka et al, 2011). These observations imply that projection neurons of common molecular profiles are further organized into microdomains within the same layer.…”