Pyramidal and nonpyramidal callosal cells in the striate cortex of the adult rat

Abstract

The aim of this study has been to determine the neuronal types (pyramidal and nonpyramidal) within the rat's visual cortex, which project through the corpus callosum. To this end, the morphology and laminar distribution of callosal cells have been investigated by combining Diamidino Yellow retrograde tracing with intracellular injection of Lucifer Yellow in slightly fixed tissue slices. The visual callosal projection arises from pyramidal cells of diverse morphology in layers II to VIb, as well as from several modified pyramids located mainly in layers II, IV (star pyramids) and VIb (horizontal or inverted pyramids and related forms of spiny stellate cells). Our results indicate that in rats, as in other mammals, several types of nonpyramidal neurons also contribute to the contralateral projection. Bitufted cells in layers II-III and V were found to project contralaterally. Moreover, a spine-free layer V cell and a sparsely spiny multipolar neuron of layer IV were also labeled. In both stellate cells, partial axonal labeling reveals that these callosal cells display a local axonal arborization. Finally, our results of retrograde transport with Diamidino Yellow and with another sensitive retrograde tracer, the beta subunit of the cholera toxin, demonstrate for the first time that the two main neuronal types of layer I participate in the callosal projection. In layer I, several small horizontal cells of the inner half of layer I and a large subpial cell displaying long radiating dendrites were also injected. The latter cell may correspond to the Cajal-Retzius cell of the adult rat. In spite of the important differences in the organization of the visual system between rodents and cats, the callosal projection in both mammals is composed of a large variety of pyramidal cells and several nonpyramidal neurons. This high morphological diversity suggests that the callosal projection is much more physiologically complex than the extracortical efferents of the visual cortex, resembling other cortico-cortical connections. The roles that the different callosal cells may play in the processing of visual information are discussed in relation to the known functions of the corpus callosum.

Cytoarchitecture of the mouse neocortex revealed by the low-molecular-weight neurofilament protein subunit

“…Similar results were also found in marmoset monkeys (Baldauf 2005;Bourne et al 2005). The non-pyramidal neuronal population that contains NFPs Brain Struct Funct (2011) 216:183-199 195 includes most likely star pyramids (Peters and Kara 1985;Cipolloni and Pandya 1991;Martínez-García et al 1994; Van der Gucht et al 2007). Previous studies on carnivores and primates located SMI-32 exclusively in a subset of pyramidal neurons known to be a class of long association projection neurons (Hof et al , 1996cNimchinsky et al 1996; Van der Gucht et al 2001.…”

Morphology and Physiology of Cortical Neurons in Layer I

“…Recent findings suggest that they are important developmentally (Ogawa et al, 1995); however, their fate in the adult cortex has not been resolved. Only a few authors have reported on CR cells in the adult brain (Condé et al, 1994;Martínez-García et al, 1994). Indeed, we have identified CR cells only in relatively young animals (7-to 9-d-old).…”

“…Martínez-García et al (1994) found that some cells in the inner half of layer I project to the contralateral visual cortex. Therefore, it may be that some of the cells we classify as cells with descending axons provide input to distant regions in addition to the collateral inputs seen in deeper cortical layers.…”

Low-frequency hippocampal–cortical activity drives brain-wide resting-state functional MRI connectivity

“…Our fMRI results and LFP latency analyses suggest that lowfrequency activity propagates downstream from ipsilateral dDG/ dHP to ipsilateral VC via the ipsilateral lateral EC (LEC) (5), before reaching contralateral VC through the corpus callosum (40,56) to finally terminate in the LGN and SC via corticothalamic and corticocollicular descending projections. The medial EC (MEC) may not actively participate in our observed responses because dHP is functionally coupled with LEC, not MEC, to establish functional gradients along the dorsoventral hippocampal axis (8).…”