Activity-induced manganese-dependent functional MRI of the rat visual cortex following intranasal manganese chloride...

Manganese-enhanced MRI (MEMRI) of the brain requires delivery of manganese into the target brain regions. It was previously shown that, following intranasal application, ongoing olfactory stimulation facilitates manganese transport along the olfactory nerve into the olfactory bulb, so bypassing the blood-brain barrier (BBB). We report on experiments to evaluate whether visual stimulation can permit manganese transport onwards from the olfactory bulb to the visual cortex. Rats in intact olfactory bulb group were reserved intact olfactory bulb, while those in olfactory bulbectomy group received bilateral bulbectomy. After intranasal MnCl(2) administration, olfactory and visual stimulations were performed on all the animals for a consecutive 20 h. The visual cortex was then examined using MEMRI. Enhanced imaging on T1WI was noted in the visual cortex of the intact olfactory bulb group. Image subtraction revealed that the signal intensity in the visual cortex of the intact olfactory bulb group was significantly higher than that of olfactory bulbectomy group. Volume of interest (VOI) analysis also showed that normalized intensities in the visual cortex of the intact olfactory bulb group were significantly higher as compared with those of the olfactory bulbectomy group. Inductively coupled plasma mass spectrometry (ICP-MS) confirmed that the manganese content in the visual cortex of the intact olfactory bulb group was increased in comparison with that of the olfactory bulbectomy group. These findings indicate that activity-induced manganese-dependent functional MRI (AIM fMRI) of the rat visual cortex can be performed following intranasal administration of manganese and demonstrate that manganese can migrate from the olfactory bulb to the visual cortex.