Immunocytochemical detection of calretinin in the claustrum and endopiriform nucleus of the chinchilla

Differential distribution of inhibitory neuron types in subregions of claustrum and dorsal endopiriform nucleus of the short-tailed fruit bat

Few brain regions have such wide-ranging inputs and outputs as the claustrum does, and fewer have posed equivalent challenges in defining their structural boundaries. We studied the distributions of three calcium-binding proteins-calretinin, parvalbumin, and calbindin-in the claustrum and dorsal endopiriform nucleus of the fruit bat, Carollia perspicillata. The proportionately large sizes of claustrum and dorsal endopiriform nucleus in Carollia brain afford unique access to these structures' intrinsic anatomy. Latexin immunoreactivity permits a separation of claustrum into core and shell subregions and an equivalent separation of dorsal endopiriform nucleus. Using latexin labeling, we found that the claustral shell in Carollia brain can be further subdivided into at least four distinct subregions. Calretinin and parvalbumin immunoreactivity reinforced the boundaries of the claustral core and its shell subregions with diametrically opposite distribution patterns. Calretinin, parvalbumin, and calbindin all colocalized with GAD67, indicating that these proteins label inhibitory neurons in both claustrum and dorsal endopiriform nucleus. Calretinin, however, also colocalized with latexin in a subset of neurons. Confocal microscopy revealed appositions that suggest synaptic contacts between cells labeled for each of the three calcium-binding proteins and latexin-immunoreactive somata in claustrum and dorsal endopiriform nucleus. Our results indicate significant subregional differences in the intrinsic inhibitory connectivity within and between claustrum and dorsal endopiriform nucleus. We conclude that the claustrum is structurally more complex than previously appreciated and that claustral and dorsal endopiriform nucleus subregions are differentially modulated by multiple inhibitory systems. These findings can also account for the excitability differences between claustrum and dorsal endopiriform nucleus described previously.

Claustrum circuit components for top-down input processing and cortical broadcast

Anterior cingulate cortex (ACC) input to the claustrum is required for top-down cognitive control of action. By virtue of its widespread cortical connectivity, the claustrum is anatomically situated to process and broadcast top-down signals from ACC to downstream cortices. To gain a deeper understanding of claustrum processing mechanisms, it is first critical to identify the projection neuron subtypes within claustrum, the intrinsic and extrinsic components regulating their firing, and the differential innervation of cortex by projection neuron subtypes. To this end, we used whole-cell patch-clamp electrophysiology in adult mouse brain slices to distinguish two spiny projection neuron subtypes in claustrum, referred to as type I and II neurons, and three aspiny interneuron subtypes, referred to as type III, IV, and V neurons. In response to optogenetic ACC afferent stimulation, type II neurons preferentially burst fire relative to type I neurons. This burst firing is calcium-dependent and is optimized by voltage-gated potassium channels. Finally, we find that visual cortices, parietal association cortex, and ACC receive input from type I and II neurons in differing proportions. These data reveal the diversity of claustrum neurons and mechanisms by which claustrum processes ACC command for spatiotemporal coordination of the cerebral cortex.