Characterization of claustral neurons by comparative gene expression profiling and dye-injection analyses

Abstract

The identity of the claustrum as a part of cerebral cortex, and in particular of the adjacent insular cortex, has been investigated by connectivity features and patterns of gene expression. In the present paper, we mapped the cortical and claustral expression of several cortical genes in rodent and macaque monkey brains (nurr1, latexin, cux2, and netrinG2) to further assess shared features between cortex and claustrum. In mice, these genes were densely expressed in the claustrum, but very sparsely in the cortex and not present in the striatum. To test whether the cortical vs. claustral cell types can be distinguished by co-expression of these genes, we performed a panel of double ISH in mouse and macaque brain. NetrinG2 and nurr1 genes were co-expressed across entire cortex and claustrum, but cux2 and nurr1 were co-expressed only in the insular cortex and claustrum. Latexin was expressed, in the macaque, only in the claustrum. The nurr1+ claustral neurons expressed VGluT1, a marker for cortical glutamatergic cells and send cortical projections. Taken together, our data suggest a partial commonality between claustral neurons and a subtype of cortical neurons in the monkey brain. Moreover, in the embryonic (E110) macaque brain, many nurr1+ neurons were scattered in the white matter between the claustrum and the insular cortex, possibly representing their migratory history. In a second set of experiments, we injected Lucifer Yellow intracellularly in mouse and rat slices to investigate whether dendrites of insular and claustral neurons can cross the border of the two brain regions. Dendrites of claustral neurons did not invade the overlying insular territory. In summary, gene expression profile of the claustrum is similar to that of the neocortex, in both rodent and macaque brains, but with modifications in density of expression and cellular co-localization of specific genes.

Frontal cortical control of posterior sensory and association cortices through the claustrum

“…Although claustrum projection neurons are glutamatergic (Brand 1981; Braak and Braak 1982; Hur and Zaborszky 2005; Watakabe et al 2014; Kim et al 2016), the downstream impact of claustrum activity on cortical layers in rodents is unclear. As such, we injected AAV-ChR2 into claustrum (Fig.…”

Anterior Cingulate Cortex Input to the Claustrum Is Required for Top-Down Action Control

“…We also detect small excitatory postsynaptic potentials in response to stimulation of sensorimotor afferents, suggesting the relevant dendritic areas are present. Moreover, claustrum dendrites extend radially in all directions (Watakabe et al, 2014), which prevents systematic truncation of particular portions of dendrite. It is possible that the claustrum may serve to propagate processed top-down input to cortical areas lower in the cortical hierarchy, such as visual cortex and parietal association cortex (PtA).…”

Interhemispheric connections between the infralimbic and entorhinal cortices: The endopiriform nucleus has limbic connections that parallel the sensory and motor connections of the claustrum

“…Some evidence, however, suggests that the claustrum and endopiriform nucleus represent two adjacent components of a single brain structure. Many peptides and gene expression profiles are continuous throughout both the claustrum and endopiriform nucleus, and these patterns are distinguishable from the overlying insular cortex (Kowiański et al, , ; Johnson et al, ; Watakabe et al, , ). Based on these observations and other data, some investigators consider the claustrum and endopiriform nucleus to be claustroamygdaloid derivatives of a common embryonic field in the pallium (Molnár and Butler, ; Reblet et al, ).…”