Functional properties, topological organization and sexual dimorphism of claustrum neurons projecting to anterior cingulate cortex

Objective: To define the physiological properties of neurons projecting from the claustrum to the anterior cingulate cortex (ACC).Design: To identify the claustrum in live slices, we used a transgenic mouse line that expresses yellow fluorescent protein (YFP)-tagged Volvox channelrhodopsin-1 at high levels within the claustrum. Claustrum cells projecting to the ACC were identified by retrograde labelling. Whole-cell patch-clamp recordings from labelled claustrum neurons were used to characterize the intrinsic electrical properties of these neurons. Cells were classified according to their intrinsic electrical properties, based on a previous classification scheme.Results: Labelled neurons were found in the claustrum but not the insular cortex. Four types of ACC-projecting neurons were identified based on action potential adaptation and waveform: strongly adapting (SA) cell types 2, 3 and 4, and moderately adapting (MA) cell type 2. Labelled cells were predominantly SA4 in the anterior (44%) and posterior (63%) claustrum, while MA2 predominated (77%) in the central claustrum. The male anterior claustrum showed a bias toward SA3 cells (53%) while the female anterior claustrum showed a bias toward SA3 cells (76%).Conclusions: There is ipsilateral dominance for ACC-projecting claustrum neurons, with the intrinsic properties of these neurons varying along the anterior–posterior axis. Sexual dimorphism was observed in ACC-projecting claustrum cells. Our results are consistent with the hypothesis that the claustrum serves as a link between the insular cortex and the ACC.