Anatomical mapping of GFAP-immunoreactive astrocytes in the whole brain of tree shrew

Astrocytes are associated with varying brain size between rodents and primates. Tree shrews (Tupaia belangeri) possess a close evolutionary relationship with primates. Yet, the anatomical distribution of astrocytes in the tree shrew brain is less clear. Here, we examined the distribution and morphology of astrocytes in the whole brain of tree shrews using glial fibrillary acidic protein (GFAP) immunofluorescence. GFAP-immunoreactive (-ir) astrocytes were present in the telencephalon, diencephalon, mesencephalon, metencephalon and myelencephalon of tree shrews. Laminar distribution of GFAP-ir astrocytes was observed in the main olfactory bulb and hippocampus. Density of GFAP-ir astrocytes was significantly different in the main olfactory bulb, accessory olfactory bulb, olfactory tubercle, cortex, hippocampus, cortical amygdaloid nucleus, hypothalamus, thalamus, superior colliculus, interpeduncular nucleus, median raphe nucleus, and parabrachial nucleus between tree shrews and mice. Compared to mice, GFAP-ir astrocytes from tree shrews exhibited higher density with more morphological complexity in the posterior hypothalamic nucleus, dorsomedial hypothalamic nucleus, ventromedial hypothalamic nucleus and periaqueductal gray, while displayed lower density with more morphological complexity in the hippocampus and substantia nigra. In the paraventricular hypothalamic nucleus and lateral hypothalamic area, GFAP-ir astrocytes revealed similar density with anatomical location-dependent differences in morphological complexity between tree shrews and mice. The present study provides the first comprehensive mapping of GFAP-ir astrocytes in the whole brain of tree shrews and demonstrates species differences in the distribution and morphology of this glial cell, providing an anatomical basis for the participation of astrocytes in numerous physiological and behavioral processes.