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Abstract

To date neuroanatomical connections have been mainly examined by means of degeneration methods and tracing techniques. Such studies require fixed processed tissue for the data analysis, and therefore they cannot be applied on the live animal. In the present study, we examined the neuronal connections in-vivo, particularly the output connections of striatum using MRI visible contrast agent (MnCl2) that is transported anterogradely through the axon, and subsequently trans-synaptically. MnCl2 (0.8 M) was injected into the caudate nucleus, and putamen in two rhesus monkeys. After the injection, the axonal transport of MnCl2 was continuously monitored for 24 hr or 45 hr using a 4.7T Biospec (Bruker, Inc) NMR scanner. We found a clear signal enhancement in the external and internal segments of the globus pallidus (Gpe and Gpi, respectively), and the substantia nigra, 24h after MnCl2 injection into the head of the caudate nucleus or putamen. Consistent with the previous anatomical studies, the spatial distribution of MnCl2 signal in globus pallidus, was different between caudate and putamen injections, with the former resulting in tracer accumulation in the dorsomedial, and the latter in the ventrolateral portion of the Gpe and Gpi. These findings were also confirmed histologically after WGA-HRP injection into the same region of the caudate or putamen, where the MnCl2 was injected. In addition, we found a strong signal increase in the thalamus and the cortical areas, particularly prefrontal and ventral inferotemporal areas, 45h after striatal injection. In conclusion, the tracer can be used to visualize neural networks with MRI.