Afferents to different layers of the dorsolateral isocortex in rats

Abstract

Fluorescent somatopetal tracers were used to infiltrate, by diffusion rather than injections, the dorsolateral cortex of one hemisphere in rats. In different animals the tracers penetrated into the cortex to different depths. We found several interesting features of the commissural system: first, there were no areas without commissural neurons. At least a few labelled cell bodies were present in a single-cell layer also in "acallosal" cortical areas. Secondly, there is a considerable variety of laminar distribution patterns of labelled perikarya in different areas. Thirdly, some cortical fields, which cytoarchitecturally appear uniform, can be subdivided according to different distributions of cell bodies with commissural projections. Fourthly, when only supragranular layers were infiltrated, labelled cell bodies were present mainly in the supragranular layers of the contralateral cortex. Infiltration of the first layer alone did not label any neurons in the contralateral cortex but did label neurons in layer VIb ipsilaterally. In the subcortex, the labelled perikarya were found in the structures already known to project directly to the cortex. In rats with the tracer restricted mainly to the supragranular layers, a conspicuously reduced labelling was found in the basal forebrain and the thalamus. In the thalami of those animals, labelled neurons were found only in paralamellar nuclei. The high sensitivity of the tracer used, together with infiltration of the entire dorsolateral cortex, allows us to conclude that probably all sources of innervation of the isocortex in rats have been seen.

Visual Sequences Drive Experience-Dependent Plasticity in Mouse Anterior Cingulate Cortex

“…V2M showed more labeling than V1 (Figure 1C; t (3) = 5.976, p = 0.0094, paired t test), confirming a larger input projection to ACC from V2M than from V1 (Wang et al, 2012). As expected, we also detected CTB in mediodorsal (MD) and anteromedial (AM) thalamus, two well-established sources of non-visual input to ACC (Delevich et al, 2015;Divac et al, 1993;Shibata and Kato, 1993;Figure S1B). Anterograde labeling of V2M and V1 projections with AAV5-CaMKII-GFP confirmed that both regions target ACC with direct, monosynaptic projections (Figures 1D and 1E).…”

Histochemical study of acute and chronic intraperitoneal nicotine effects on several glycolytic and Krebs cycle dehydrogenase activities in the frontoparietal cortex and subcortical nuclei of the rat brain

“…There existed several mismatches among dehydrogenase maps of the tested activities, the cortical cytoarchitecture, and the laminar patterns described in studies on local glucose utilization (basal and post‐sensorial stimulation) and on nicotine receptor localization. Layers II and III contain a large quantity of synapses between layer III and layer V pyramidal apical dendrites, and the ascending afferent cortical fibers, collateral pyramidal axons and cortical non‐pyramidal axonal endings; and layers IV and V also possess a very high number of synaptic connections on granular neuronal dendrites and basal layer V pyramidal neurons (Valverde, 1986; Divac et al, 1987, 1995; Fabri and Burton, 1991). All of these neuronal connections were in parallel with high presynaptic and postsynaptic mitochondrial content, which could be part of the morphofunctional basis of the nicotine effect that we describe.…”

Cortical Layer VII and Persistent Subplate Cells in Mammalian Brains

“…These deep layer VI cells participate in long distance corticocortical connections in guinea pigs, as do layer VII cells in rats and prairie voles [Divac et al, 1987[Divac et al, , 1995Vandevelde et al, 1996;Reep and Kirkpatrick, 1999]. Furthermore, as in rats and prairie voles, the majority of corticocortical axons in guinea pigs travel in the deep gray matter rather than in the white matter [Vandevelde et al, 1996;Reep and Kirkpatrick, 1999].…”

“…Neurons of layer VII participate in local and long-distance ipsilateral corticocortical connections in rats, and apparently do not send projections to subcortical regions [Divac et al, 1987[Divac et al, , 1995Reep et al, 1987Reep et al, , 1990Reep et al, , 1994Reep and Goodwin, 1988;Valverde et al, 1989;Vandevelde et al, 1996;Clancy and Cauller, 1999]. This contrasts with the neurons of layer VI that project to the thalamus and have sparse corticocortical connections [Divac et al, 1987;Reep et al, 1990Reep et al, , 1994Staiger et al, 1996].…”

“…This raises the possibility that in some cortical areas in some taxa, subplate survivors are present in the gray matter, but blend in rather inconspicuously with the deep portion of layer VI rather than forming a separate layer VII. This cryptic population of subplate survivors might also participate in long distance cortical connections, as do layer VII neurons in rats and prairie voles [Divac et al, 1987[Divac et al, , 1995Vandevelde et al, 1996;Reep and Kirkpatrick, 1999].…”