Abstract
The striatum is a major component of the basal ganglia and is associated with motor and cognitive functions. Striatal pathologies have been linked to several disorders, including Huntington’s, Tourette’s syndrome, obsessive–compulsive disorders, and schizophrenia. For the study of these striatal pathologies different animal models have been used, including rodents and non-human primates. Rodents lack on morphological complexity (for example, the lack of well defined caudate and putamen nuclei), which makes it difficult to translate data to the human paradigm. Primates, and especially higher primates, are the closest model to humans, but there are ever-increasing restrictions to the use of these animals for research. In our search for a non-primate animal model with a striatum that anatomically (and perhaps functionally) can resemble that of humans, we turned our attention to the tree shrew. Evolutionary genetic studies have provided strong data supporting that the tree shrews (Scadentia) are one of the closest groups to primates, although their brain anatomy has only been studied in detail for specific brain areas. Morphologically, the tree shrew striatum resembles the primate striatum with the presence of an internal capsule separating the caudate and putamen, but little is known about its neurochemical composition. Here we analyzed the expression of calcium-binding proteins, the presence and distribution of the striosome and matrix compartments (by the use of calbindin, tyrosine hydroxylase, and acetylcholinesterase immunohistochemistry), and the GABAergic system by immunohistochemistry against glutamic acid decarboxylase and Golgi impregnation. In summary, our results show that when compared to primates, the tree shrew dorsal striatum presents striking similarities in the distribution of most of the markers studied, while presenting some marked divergences when compared to the rodent striatum.
Highlights
The mammalian striatum is a major component of the basal ganglia and contains its major receptive nuclei, the caudate, and the putamen
Western-blot experiments showed that the antibodies produced bands that were located at the same level in the gel for both rat striatum and tree shrew brain protein extracts
We found a great variability in the total number of tyrosine hydroxylase (TH)-ir cells between the two animals used for neuronal counts [animal #1 had 175 TH immunoreactivity (TH-ir) cells/series which yields a total of 1050 TH-ir cells for the whole dorsal striatum; animal #2 had 291 TH-ir cells/series which yields a total of 1746 TH-ir cells]
Summary
The mammalian striatum is a major component of the basal ganglia and contains its major receptive nuclei, the caudate, and the putamen These nuclei are the target of several areas of the mammalian brain including the cortex, mesencephalon, and thalamus (Kawaguchi et al, 1995; Joel and Weiner, 2000). Even when there is no complete segregation of the target areas, the caudate and putamen present two distinguishable types of compartments with their own specific properties These compartments are known as the striosomes (patch) and matrix, which receive preferentially different inputs and contain cells that express different markers (Graybiel and Ragsdale, 1983; Donoghue and Herkenham, 1986; Bolam et al, 1988; Ragsdale and Graybiel, 1988; Gerfen, 1989; Hirsch et al, 1989; Graybiel, 1990; Kubota and Kawaguchi, 1993; Holt et al, 1997). Ventral to the caudate and putamen is an area of the striatum known as the “ventral striatum.” Different nuclei have been suggested to be part of the ventral striatum (Heimer and Wilson, 1975; Heimer et al, 1982; Haber and McFarland, 1999; Fudge and Haber, 2002), of which the most prominent is the accumbens nucleus
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