Fractionated manganese injections: Effects on MRI contrast enhancement and physiological measures in C57BL/6 mice

Max Planck Institute of Psychiatry, Munich, Germany.
NMR in Biomedicine (Impact Factor: 3.04). 10/2010; 23(8):913-21. DOI: 10.1002/nbm.1508
Source: PubMed


Manganese-enhanced MRI (MEMRI) is an increasingly used imaging method in animal research, which enables improved T(1)-weighted tissue contrast. Furthermore accumulation of manganese in activated neurons allows visualization of neuronal activity. However, at higher concentrations manganese (Mn2+) exhibits toxic side effects that interfere with the animals' behaviour and well-being. Therefore, when optimizing MEMRI protocols, a compromise has to be found between minimizing side effects and intensifying image contrast. Recently, a low concentrated fractionated Mn2+ application scheme has been proposed as a promising alternative. In this study, we investigated effects of different fractionated Mn2+ dosing schemes on vegetative, behavioural and endocrine markers, and MEMRI signal contrast in C57BL/6N mice. Measurements of the animals' well-being included telemetric monitoring of body temperature and locomotion, control of weight and observation of behavioural parameters during the time course of the injection protocols. Corticosterone levels after Mn2+ application served as endocrine marker of the stress response. We compared three MnCl2  x 4H2O application protocols: 3 times 60 mg/kg with an inter-injection interval of 48 h, six times 30 mg/kg with an inter-injection interval of 48 h, and 8 times 30 mg/kg with an inter-injection interval of 24 h (referred to as 3 x 60/48, 6 x 30/48 and 8 x 30/24, respectively). Both the 6 x 30/48 and the 8 x 30/24 protocols showed attenuated effects on animals' well-being as compared to the 3 x 60/48 scheme. Best MEMRI signal contrast was observed for the 8 x 30/24 protocol. Together, these results argue for a fractionated application scheme such as 30 mg/kg every 24 h for 8 days to provide sufficient MEMRI signal contrast while minimizing toxic side effects and distress.

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    • "In vivo MEMRI was performed essentially as described before (Grünecker et al., 2010, 2012). Briefly, minimum 2 weeks after the last testing animals received intraperitoneal injections of 30 mg/kg MnCl2 (Sigma, Germany) every 24 h over the course of 8 consecutive days. "
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    • "The Mn 2+ administration protocol was selected to provide sufficient enhancement of brain tissue signal, i.e., 30%–50%, with minimum effect on animal well-being. This criterion was based on reports on fractionated MEMRI in rats (Bock et al. 2008; Inui-Yamamoto et al. 2010), mice (Grünecker et al. 2010), and on our own pilot studies. A stock solution of 10 mM MnCl 2 (Sigma) in DDW was prepared. "
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