In vivo 3D MRI staining of mouse brain after subcutaneous application of MnCl2.
Magn Reson Med. 2002 Nov;48(5):852-9. PMID: 12418000
Watanabe T, Natt O, Boretius S, Frahm J, Michaelis T.

The objective of this paper was to examine the feasibility of using Mn²⁺ as an MRI contrasting agent without the need to disrupt the Blood Brain Barrier as has been done in other studies.  This would allow visualization of brain structures after systemic application of Mn²⁺, without the need for catheterization of the carotid artery to deliver mannitol solution for disruption of the BBB.

Results:

·         Areas with direct access to systemic circulation (anterior pituitary, choroid plexus) show strong increase (200%) at 6hr point.  Areas behind blood brain barrier (olfactory bulb, hippocampal CA3 region) take longer (24hrs) and show a weaker increase (10-25%)
·         Observed tract-like structures in the olfactory bulb – interpreted as evidence for axoplasmic transport of Mn²⁺
·         Saw bright superficial layers in the cerebellum similar to purkinje cell layers and dark deep layers representative of white matter.
·         Saw an increase in CA3 (input region), but not in CA1 (output region)

Conclusions:

·         MRI enhancement of selective areas is by differential uptake of Mn²⁺ through Ca²⁺ channels during action potentials.  Differences in Mn²⁺ content reflect differences in neuron activity during the time after the MnCl₂ injection
·         Differences may also rely on differential expression of enzymes that utilize Mn²⁺ (e.g. glutamine synthetase contains 8 Mn²⁺ ions and contains ~80% of Mn in the brain, SNR was higher in CA3 which is known to have high expression of manganese superoxide dismutase and lower in CA1 that doesn’t)

Methods:  Mice were given subcutaneous injections of MnCl₂.  After IP anesthesia, MRI was performed at 0, 6, 24, and 48hrs in order to compare the Mn²⁺ enhancement in 13 different regions of the brain.  Evaluation of Mn²⁺ enhancement was done by comparing the Signal to Noise ratio, where SNR=(Signal/StdDev)

-DH