Identification of Mouse Claustral Neuron Types Based on Their Intrinsic Electrical Properties

Abstract

Although its dense connections with other brain areas suggests that the claustrum is involved in higher-order brain functions, little is known about the properties of claustrum neurons. Using whole-cell patch clamp recordings in acute brain slices of mice, we characterized the intrinsic electrical properties of more than 300 claustral neurons and used unsupervised clustering of these properties to define distinct cell types. Differences in intrinsic properties permitted separation of interneurons (INs) from projection neurons (PNs). Five subtypes of PNs could be further identified by differences in their adaptation of action potential (AP) frequency and amplitude, as well as their AP firing variability. Injection of retrogradely transported fluorescent beads revealed that PN subtypes differed in their projection targets: one projected solely to subcortical areas while three out of the remaining four targeted cortical areas. INs expressing parvalbumin (PV), somatostatin (SST), or vasoactive intestinal peptide (VIP) formed a heterogenous group. PV-INs were readily distinguishable from VIP-INs and SST-INs, while the latter two were clustered together. To distinguish IN subtypes, an artificial neural network was trained to distinguish the properties of PV-INs, SST-INs, and VIP-INs, as independently identified through their expression of marker proteins. A user-friendly, machine-learning tool that uses intrinsic electrical properties to distinguish these eight different types of claustral cells was developed to facilitate implementation of our classification scheme. Systematic classification of claustrum neurons lays the foundation for future determinations of claustrum circuit function, which will advance our understanding of the role of the claustrum in brain function.

Topographic gradients define the projection patterns of the claustrum core and shell in mice

“…However, the density of PV cell bodies and neuropil labeling decreases drastically in both the dorsal and ventral axes implying that claustrocortical neurons projecting to ALM, MOp, ENTm, and ENTl may receive less prominent PV‐mediated inhibition. The presence of other interneurons containing calretinin, vasoactive intestinal polypeptide (VIP), NPY, SST, and cholecystokinin have been shown to exist in the claustrum (Graf, Nair, Wong, Tang, & Augustine, 2020; Kowiański et al, 2008; Real et al, 2003). Calretinin neurons show a similar spatial distribution to what we describe here for SST (Druga, Salaj, Barinka, Edelstein, & Kubová, 2015).…”

A functional logic for neurotransmitter co-release in the cholinergic forebrain pathway

“…To isolate cholinergic responses, recordings were performed in the presence of a glutamate receptor blocker (kynurenic acid, KYN; 1 µM) and GABA receptor blocker (Gabazine, GBZ; 10 µM). The claustrum consists of multiple types of projection neurons and interneurons 16 . A trained classifier was applied to whole-cell patch clamp measurements of intrinsic electrical properties to identify neurons that project to cortical or non-cortical targets, as well as to identify the three known types of local interneurons 16 .…”

“…Below we briefly describe this model. We first generate synaptic weight matrices W with N = 300 neurons (with excitatory and inhibitory neurons in the ratio 9:1 as empirically determined 36 ) as detailed in Hennequin et al, 2014 31 .…”

Topographic gradients define the projection patterns of the claustrum core and shell in mice

“…However, with the NPY-GFP mouse used here, there was dense neuropil and cell body labeling that outlined the claustrum core and shell (Figures 12 and 13). A recent study showed that the intrinsic electrical properties of PV, SST, and VIP interneurons in the claustrum were distinct from each other (Graf et al, 2020), similar to cortex. However, to the best of our knowledge, no study has tested or compared the connectivity of SST, NPY, or VIP cells with different claustrocortical connections.…”

“…However, the density of PV cell bodies and neuropil labelling decreases drastically in both the dorsal and ventral axes implying that claustrocortical neurons projecting to ALM, MOp, ENTm, and ENTl may receive less prominent PV-mediated inhibition. The presence of other interneurons containing calretinin, vasoactive intestinal polypeptide (VIP), NPY, SST, and cholecystokinin have been shown to exist in the claustrum (Graf et al, 2020;Kowiański et al, 2008;Real et al, 2003).…”