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Comparative anatomical and histological study of the corpus striatum in humans and rhesus monkeys

When comparing human to other mammalian brain, it is postulated that the older, „diencephalic brain“ is highly conserved among species, whilst the more „recent“ (neo)cortical brain differs in a significant extent. Although of telencephalic origin, the basal ganglia are also often considered conserved, as they represent a universal cortico-thalamo-cortical co-ordination system. Since basal ganglia and the cortex are tightly interconnected, even the slightest evolutionary driven changes in the cortex would affect the basal ganglia by means of the subtle microarchitectural changes. Therefore, our objective was to try to identify those hypothesized changes. Our aim was to compare distinctive regions of the corpus striatum in human specimens with the corresponding regions in rhesus monkey (Maccaca mulatta) regvrding the brain metvbolism and number of neurons. We chose the striatum becvuse it represents the main input nucleus to the basal ganglia system. We microscopically compared the striatum of macaca mulatta (n=6) and homo sapiens (n=3), using specimens provided by Mikula et al., with no co-morbidities that would interfere with the structure of the region of interest. The coronal slices were stained immunohistochemically using cytochrome oxidase primary antibodies. Specimens were photographed in a high resolution format and analysed digitally using the Cell Profiler Analyst software. Our results revealed a statistically significant lesser neuronal count per area unit in distinctive striatal regions in macaques compared to analogous regions in humans: medial putamen (p=0, 001) and dorsolateral caudate (p=0, 002). No significant differences regarding the neuronal count were observed in the ventral putamen, ventromedial caudate and dorsolateral putamen, except for the discrete striosomal islets in the putaminal convexity, whose dorsal half was significantly hyperneuronal in macaques (p=0, 001), whereas its ventral half's neural count was slightly greater in human specimens with a somehow weaker statistical significance (p=0, 004). These findings suggest that significant microarchitectural differences may exist between the striatum of close primate relatives, humans and rhesus monkeys. Hyperneuronal areas in humans compared to macaques are actually somatotropic regions implicated in forelimb movement and prefrontal loop of the basal ganglia. Discrete dorsal portion of putaminal convexity in macaques that is hyperneuronal compared to humans is actually the region responsible for hindlimb movement.

corpus striatum; basal ganglia; rhesus monkey; anatomy; Cell Profiler

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