The distribution of manganese-54 in fetal, young and adult rats

In vivo detection of neuroarchitecture in the rodent brain using manganese-enhanced MRI

Visualizing brain anatomy in vivo could provide insight into normal and pathophysiology. Here it is demonstrated that neuroarchitecture can be detected in the rodent brain using MRI after systemic MnCl2. Administration of MnCl2 leads to rapid T1 enhancement in the choroid plexus and circumventricular organs, which spreads to the CSF space in ventricles and periventricular tissue. After 1 day, there was MRI enhancement throughout the brain with high intensity in the pituitary, olfactory bulb, cortex, basal forebrain, hippocampus, basal ganglia, hypothalamus, amygdala, and cerebellum. Contrast obtained enabled visualization of specific features of neuroarchitecture. The arrowhead structure of the dentate gyrus as well as the CA1-CA3 region of the hippocampus and layers in cortex, cerebellum, as well as the olfactory bulb could be readily observed. Preliminary assignments of olfactory bulb layers, cortical layers in frontal and somatosensory cortex, and cerebellum were made. Systemic MnCl2 leads to MRI visualization of neuroarchitecture nondestructively.

Manganese ion enhances T1-weighted MRI during brain activation: an approach to direct imaging of brain function

Present techniques for functional MRI rely on detecting changes in hemodynamics that result as a consequence of brain activation. It would be useful if MRI techniques could be developed that enable imaging of a parameter directly related to neuronal activity. Influx of calcium into neurons is necessary for release of neurotransmitters. Divalent manganese ions (Mn2+) can enter cells through voltage-gated calcium channels and Mn2+ is paramagnetic. Mn2+ accumulation in brain due to activation should alter relaxation times offering an approach to sensitize MRI to calcium influx in the brain. To test this idea, T1-weighted MRI was obtained from the rat brain in the presence of a continuous intravenous infusion of 3.6 mumol/min MnCl2. In the anesthetized rat brain, signal enhancement was detected in regions corresponding to ventricles. Activation of the brain with glutamate led to increase in MRI signal intensity in the brain to 238 +/- 23% of the original. This increase in signal was dependent on the presence of MnCl2 and was not due to changes in blood flow. It was necessary to break the blood brain barrier with mannitol to make Mn2+ accessible to the active sites for efficient detection. Enhancement of MRI signal in the brain was also detected with decreasing anesthesia and with somatosensory stimulation. Due to the slow clearance of Mn2+ from the stimulated region of the brain, MRI enhancement could also be detected after stimulation that occurred on awake, behaving rats outside the magnet. These data indicate that MnCl2 shows potential as a MRI contrast agent that is directly sensitive to brain activation.

Localization in rat brain of the trace metals, zinc and manganese, after intracerebroventricular injection

Autoradiographic studies of rat brain, after 65ZnCl2 or 54MnCl2 injection into the lateral ventricle, revealed that 65Zn and 54Mn were transferred freely through the cerebrospinal and extracellular fluid compartments; both tracers appeared in all the ventricles 1 h after injection. At 6 days after injection, 65Zn was concentrated in the hippocampal formation and hypothalamic nuclei but not in the cerebral cortex and superior colliculus of the ipsilateral hemisphere, with a lower uptake into contralateral hemisphere except for the hypothalamic nuclei. 54Mn was concentrated in some brainstem nuclei, such as the red and pontine reticular nuclei, to about the same extent in both hemispheres. These results suggest that both metals were taken up gradually into brain mainly via the cerebrospinal fluid. Relatively high uptake of 65Zn into the cerebral cortex and superior colliculus after intravenous injection suggests uptake in those regions is through two blood/brain barriers.

Saturable transport of manganese(II) across the rat blood-brain barrier

Unanesthetized adult male rats were infused intravenously with solutions containing 54Mn (II) and one of six concentrations of stable Mn(II). The infusion was timed to produce a near constant [Mn] in plasma for up to 20 min. Plasma was collected serially and on termination of the experiment, samples of CSF, eight brain regions, and choroid plexus (CP) were obtained. Influx of Mn (JMn) was calculated from uptake of 54Mn into tissues and CSF at two different times. Plasma [Mn] was varied 1,000-fold (0.076-78 nmol/ml). Over this plasma concentration range, JMn increased 123 times into CP, 18-120 times into brain, and 706 times into CSF. CP and brain JMn values fit saturation kinetics with Km (nmol/ml) equal to 15 for CP and 0.7-2.1 for brain, and Vmax (10(-2) nmol.g-1.s-1) of 27 for CP and 0.025-0.054 for brain. Brain JMn except at cerebral cortex had a nonsaturable component. CSF JMn varied linearly with plasma [Mn]. These findings suggest that Mn transport into brain and CP is saturable, but transport into CSF is nonsaturable.

Magnetic resonance imaging studies of the brains of anesthetized rats treated with manganese chloride

An understanding of the distribution of manganese ions in the brain is of interest in connection with the development of an understanding of the neurotoxicity of this element. Information about the time dependent biodistribution of manganese ions in the brains of intact rats subsequent to single IP injections of MnCl2 has been obtained from magnetic resonance imaging (MRI) studies. The enhanced MRI contrast is based on the reduction in the spin lattice relaxation time (T1) of water protons which exchange into the coordination sphere of the manganese ions. These studies indicate rapid and significant accumulations of water accessible manganese in the ventricles, the pineal gland, and the pituitary gland. The rapid appearance of high levels of manganese in the ventricular cerebrospinal fluid indicates that manganese readily crosses the filtration barrier of the choroid plexus and is thereafter apparently absorbed by the ependymal surfaces of the ventricles and transported to the subarachnoid space.

Influence of polyaminocarboxylic acids on the removal of manganese-54 from the body organs of sham-operated and partially hepatectomized rats

EDTA, 1,2-cyclohexylenediamine tetra-acetic acid (CDTA), hexamethylene 1,6-diamine N,N,N',N'-tetra-acetic acid (HDTA), diethylene-triamine pentaacetic acid (DTPA) and nitrilotriacetic acid (NTA) were examined for the removal of manganese-54(54Mn) from some organs of sham-operated and partially hepatectomized rats in early manganese (Mn) poisoning. CDTA was found to be most effective in removing 54Mn from the liver of both sham-operated and hepatectomized rats. These chelating agents also lowered the Mn levels in kidney, spleen and brain of poisoned rats. Although a significantly higher accumulation of Mn was observed in hepatectomized rats, there was no significant difference in the efficiency of the chelating agents in removing Mn from the body organs of poisoned animals of both the sham-operated and hepatectomized groups. An attempt has been made to seek a possible correlation between % removal of Mn by various polyaminocarboxylic acids and their corresponding stability constants.