Abstract
Day-active tree shrews have a well-developed internal capsule (ic) that clearly separates the caudate nucleus (Cd) and putamen (Pu). The striatum consists of the Cd, ic, Pu, and accumbens nucleus (Acb). Here, we characterized the cytoarchitecture of the striatum and the whole-brain inputs to the Cd, Pu, and Acb in tree shrews by using immunohistochemistry and the retrograde tracer Fluoro-Gold (FG). Our data show the distribution patterns of parvalbumin (PV), nitric oxide synthase (NOS), calretinin (CR), and tyrosine hydroxylase (TH) immunoreactivity in the striatum of tree shrews, which were different from those observed in rats. The Cd and Pu mainly received inputs from the thalamus, motor cortex, somatosensory cortex, subthalamic nucleus, substantia nigra, and other cortical and subcortical regions, whereas the Acb primarily received inputs from the anterior olfactory nucleus, claustrum, infralimbic cortex, thalamus, raphe nucleus, parabrachial nucleus, ventral tegmental area, and so on. The Cd, Pu, and Acb received inputs from different neuronal populations in the ipsilateral (60, 67, and 63 brain regions, respectively) and contralateral (23, 20, and 36 brain regions, respectively) brain hemispheres. Overall, we demonstrate that there are species differences between tree shrews and rats in the density of PV, NOS, CR, and TH immunoreactivity in the striatum. Additionally, we mapped for the first time the distribution of whole-brain input neurons projecting to the striatum of tree shrews with FG injected into the Cd, Pu, and Acb. The similarities and differences in their brain-wide input patterns may provide new insights into the diverse functions of the striatal subregions.
Highlights
The striatum is composed of the ventral and dorsal striatum (Ni et al, 2018)
The present study found that PV, NOS, CR, and TH had a wide distribution within the striatum of tree shrews and rats
The distribution of PVir neurons and fibers in the striatum has been investigated previously (Rice et al, 2011; Ni et al, 2018), our study revealed that the density of PV-ir neurons was different in the distinct subregions of the tree shrew striatum and similar in the various parts of the rat striatum
Summary
The ventral striatum contains the accumbens nucleus (Acb). The dorsal striatum is subdivided into the caudate nucleus (Cd), internal capsule (ic), and putamen (Pu) (Provost et al, 2015). A welldeveloped ic clearly separates the Cd and Pu in primates and humans, whereas the underdeveloped ic is scattered in most regions of the rostral and middle parts of the dorsal striatum in rodents (Ni et al, 2018). The Cd is important in many functions, such as motor response (Kesner and Gilbert, 2006), motor skill learning (Choi et al, 2020), and psychiatric illnesses (Vostrikov and Uranova, 2020). The Pu seems to participate in Afferent Inputs to Striatum motor learning (Liebrand et al, 2020), auditory responses (Salisbury et al, 2021), cocaine addiction (Ersche et al, 2021), and psychiatric disorders (Kolomeets and Uranova, 2020). The Acb is involved in motor control (Sawada et al, 2015), reward processing (Muench et al, 2018), motivation (Baumgartner et al, 2021), addiction (Crofton et al, 2021), mental disorders (Terrillion et al, 2017), and social defeat stress (Yin et al, 2021)
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