The callosal projection in cat visual cortex as revealed by a combination of retrograde tracing and intracellular injection

Abstract

The neuronal composition of callosally projecting cells in cat visual cortex was determined with a combination of retrograde labelling and intracellular injection. Fluorescent tracers were stereotaxically injected into the proximity of the area 17/18 border, corresponding to the representation of the visual vertical meridian. In fixed slice preparations of homotopic regions of the contralateral hemisphere retrogradely labelled cells were filled with Lucifer Yellow. Of more than a hundred injected cells a morphological variety of pyramidal cells, located in cortical layers II-IV and VI, constituted the prevalent cell class in the contralateral projection. A minor proportion of spiny stellate cells was encountered in layer IV. Despite the presence of a contralaterally projecting smooth stellate cell, presumed to be a basket cell, it is concluded that the efferents to contralateral visual cortex predominantly arise from pyramidal and spiny stellate cells. Thus, in agreement with findings from anterograde degeneration studies, the interhemispheric pathway most likely conveys a direct excitatory input to postsynaptic target cells.

Cells in Auditory Cortex that Project to the Cochlear Nucleus in Guinea Pigs

“…7). It was of particular interest to determine whether the labeled pyramidal cells possess terminal dendritic tufts in layer I, because the presence of a tuft distinguishes two major classes of layer V pyramidal cells in many cortical areas (McCormick et al 1985;Agmon and Connors 1989;Chagnac-Amitai et al 1990;Kasper et al 1994;Hefti and Smith 2000). Whereas only a minority of cells was labeled sufficiently to distinguish pyramidal types, dendritic tufts in layer I were labeled in numerous cases (Fig.…”

“…Correlated physiological and morphological studies have separated pyramidal cells into two major types (McCormick et al 1985;Mitani et al 1985;Agmon and Connors 1989;Chagnac-Amitai et al 1990;Larkman and Mason 1990;Ojima et al 1992;Kasper et al 1994;Smith 2000, 2003). In the most common terminology, these types are named according to their characteristic responses to current injection: regular spiking (RS) and intrinsically bursting (IB).…”

“…In the most common terminology, these types are named according to their characteristic responses to current injection: regular spiking (RS) and intrinsically bursting (IB). The two types have different dendritic morphologies and membrane properties, receive different patterns of thalamic inputs, different patterns of inhibitory inputs, and have different patterns of local axonal projections (McCormick et al 1985;Mitani et al 1985;Agmon and Connors 1989;Chagnac-Amitai et al 1990;Ojima et al 1992;Wang and McCormick 1993;Kasper et al 1994;Hefti and Smith 2000). IB cells have an apical dendrite with a prominent tuft in layer I.…”

“…In contrast, RS cells lack a prominent layer I dendritic tuft. Nontufted cells are often associated with corticocortical and corticostriatal projections (e.g., Hallman et al 1988;Hü bener and Bolz 1988;Buhl and Singer 1989;Hü bener et al 1990;Ojima et al 1992;Winer and Prieto 2001). The many differences imply that tufted and nontufted cells play distinct functional roles.…”

“…It remains to be determined whether these cells correspond to IB and RS physiological classes, but this seems likely given the presence of such a correlation in a variety of many labeled cells with small cell bodies, which have been associated with nontufted morphology and RS physiology (e.g., Chagnac-Amitai et al 1990;Ojima et al 1992;Hefti and Smith 2000;Winer and Prieto 2001). Additional experiments, perhaps with retrograde Btagging^of AC-CN cells followed by intracellular labeling in a fixed slice (e.g., Hallman et al 1988), could clarify the dendritic morphology of the cells with small somas and demonstrate whether nontufted cells project to the CN.…”