MEMRI Detects Neuronal Loss in MPTP-Intoxicated Mice.
Aditya N Bade1, Katherine Olson1, Charles Schutt1, Jingdong Dong2, R Lee Mosley1, Howard E Gendelman1, Michael D Boska1,3, and Yutong Liu1,3

1Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Omaha, NE, United States, 2Second Affiliated Hospital, Dalian Medical University, Dalian, China, People's Republic of, 3Department of Radiology, University of Nebraska Medical Center, Omaha, Omaha, NE, United States

Synopsis

This study showed that neuronal loss in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injected mice as confirmed by immunohistology caused signal change in manganese-enhanced MRI (MEMRI). Both gliosis and neuronal loss occur in the progress of neurodegenerative diseases. Previous studies have shown that MEMRI signal is associated with he gliosis in rodents. With the findings in this study, it is demonstrated the combined pathologic effects of neuronal damage and gliosis determine MEMRI results. The study suggested that MEMRI is an in vivo imaging tool to study the progress of neurodegenerative disease in rodents.

Introduction

MEMRI in normal animals provides novel information relevant to anatomical, integrative, and functional assessments of neural connectivity. Significant works have focused on the use of MEMRI for studies of pathobiology of neurodegenerative diseases. However, the cellular mechanisms underlying the MEMRI signal changes caused by neuropathology are still controversial. We have demonstrated that neurons stimulated by astrocytic activation represent a significant cellular response to induce MEMRI signal enhancement in brain inflammation1. With this in mind, MEMRI was successfully used to detect HIV-1 infection induced inflammation in humanized mice2. The goal of this study was to delineate cellular mechanisms of MEMRI signals as neuronal injury progresses. Neuronal injury was generated by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injection in mice as a model of Parkinson’s disease. Neuronal loss and gliosis in this mouse model is well-characterized3,4.

Materials and Methods

MPTP (18 mg/kg x 4 doses at 2 hrs/dose, n = 6) or PBS (10 ml/kg, n = 5) was injected into mice via i.p. route. MnCl2 (60 mg/kg) was injected i.p. 4 hours after MPTP/PBS. The 2nd MnCl2 injection was carried out 24 hours after MPTP/PBS. MRI was performed 48 hours after MPTP/PBS on a 7T/21 cm MRI scanner (Bruker, Billerica, MA). Mice were scanned using T1-wt MRI (3D FLASH, TR = 20 ms, flip angle = 20o). The T1-wt images were then registered to a MEMRI-based rat brain atlas and compared by t-tests for regional MRI signal enhancement between PBS controls and MPTP injected mice. After MRI, animals were euthanized and brains recovered for immunohistological validation. Thirty μm frozen sections were labeled with rabbit polyclonal antibody for tyrosine hydroxylase (TH+). Images were captured with 10× objective using Nuance EX multispectral imaging system fixed to a Nikon Eclipse E800.

Results

Fig 1 shows the averaged MEMRI enhancement in MPTP mice (Fig 1A) and PBS controls (Fig 1B). Signal intensities of substantia nigra (SN) and hypothalamus (HY) were lower in MPTP mice compared to controls (P<0.05, Fig 2A). In addition, signal intensities of motorsensory cortex (MS-Ctx), and striatum (STR) were higher in MPTP mice compared to controls (P<0.05, Fig 2B). Dopaminergic (DA) neuron loss was observed in MPTP mice (Fig 3).

Discussion

After MPTP intoxication, significant DA neuron loss occurs within the SN and striatum and the rate of neurodegeneration reaches maximum at 2 days post-injection3. Gliosis is also significant by day 24. Our previous study2 demonstrated MEMRI enhancement correlates with astrocyte activation. In another study3, we determined that, gliosis and neuronal damage occur simultaneously, but offset the effects of neuronal activation and astrocyte activation. The combined pathologic effects determine MEMRI results. This study indicated at 2 days after MPTP injection, the effect of neuronal loss outweighed gliosis producing decreased MEMRI signal intensity within the SN and HY. Immunohistological analysis confirmed the neuronal loss in SN. The signal enhancement on MS-Ctx and STR suggested elevated glial activation. We are working on immunohistology to confirm the finding. These results confirm the ability of MEMRI to detect frank neurodegeneration and areas of neuroinflammation, which is proven by our previous studies1,2 , as well as documenting the effects of MPTP on HY, an unexpected finding.

Acknowledgements

This study is partially supported by K25 MH08985, NIH R01 NS070190

References

1. Bade et al, Improved visualization of neuronal injury following glial activation by manganese enhanced MRI, J Neuroimmune Pharmacol. 2013.

2. Bade et al, Manganese-Enhanced Magnetic Resonance Imaging Reflects Brain Pathology during Progressive HIV-1 Infection of Humanized Mice, Mol Neurobiol. 2015.

3. Jackson-Lewis et al, Time course and morphology of dopaminergic neuronal death caused by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, Neurodegeneration. 1995.

4. Francis et al, Neuroglial responses to the dopaminergic neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mouse striatum, Neurotoxicol Teratol. 1995

Figures

Figure 1. Averaged MEMRI enhancement in MPTP injected mice (A) and PBS controls (B).

Figure 2. Pixels showing significant MEMRI enhancement decrease (A) and increase (B) superposed on MEMRI images.

Figure 3. TH+ neurons in PBS and MPTP treated mice



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
1240