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

Manganese‐enhanced MRI (MEMRI) is an increasingly used imaging method in animal research, which enables improved T₁‐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 · 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 × 60/48, 6 × 30/48 and 8 × 30/24, respectively). Both the 6 × 30/48 and the 8 × 30/24 protocols showed attenuated effects on animals' well‐being as compared to the 3 × 60/48 scheme. Best MEMRI signal contrast was observed for the 8 × 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. Copyright © 2010 John Wiley & Sons, Ltd.