In vivo 3D MRI staining of mouse brain after subcutaneous application of MnCl₂

Abstract

Follow-up T 1 -weighted 3D gradient-echo MRI (2.35 T) of murine brain in vivo (N ‫؍‬ 5) at 120 m isotropic resolution revealed spatially distinct signal increases 6 -48 hr after subcutaneous application of MnCl 2 (20 mg/kg). The effects result from a shortening of the water proton T 1 relaxation time due to the presence of unchelated paramagnetic Mn 2؉ ions, which access the brain by systemic circulation and crossing of the blood-brain barrier (BBB Progress in neurogenetics has renewed interest in imaging neuroscience because 1) it can improve our understanding of the structure and function of the central nervous system in the context of genetic information, and 2) it can be used to evaluate novel therapeutic interventions in active animals. In either case, gene technology has led to the use of an increasing number of mutant mice, which requires the use of in vivo assessments such as, for example, those offered by noninvasive MRI techniques. Several in vivo MRI studies of mouse brain have demonstrated potential for providing detailed morphologic insights (1-6). Nevertheless, the anatomic information obtainable is limited and a considerable number of abnormalities may still have to be verified by other methods because of their microscopic size, sparse distribution, and/or poor MRI detectability caused by subtle alterations of MR properties. Therefore, additional means of achieving soft-tissue contrast enhancement or MRI staining (7) by exogenous compounds are highly desirable.Because common MRI contrast agents consist of chelated paramagnetic ions, their systemic application does not lead to a penetration of the blood-brain barrier (BBB). Such contrast agents are safe for human studies and can be used clinically to detect disturbances of the BBB. The situation differs for free divalent metal ions, which exhibit variable degrees of neurotoxicity. In particular, high-resolution autoradiography has demonstrated that manganese accumulates in the olfactory bulb, olfactory nuclei, inferior colliculi, amygdala, thalamus, hippocampal formation, and cerebellum (8 -12). Upon bolus injection, Mn 2ϩ enters the brain across the capillary endothelium (13-15) and leads to biologic halflives of 51-74 days (9). In conjunction with its well-known capabilities as a paramagnetic MRI contrast agent that effectively reduces the T 1 relaxation time of accessible water protons (16), these data suggest that Mn 2ϩ is a good candidate for MRI staining of animal brain after systemic administration.Previous MRI studies of manganese in animal brain addressed its regional distribution and cerebral toxicity during an acute phase 3-22 hr after Mn 2ϩ exposure in rat brain (17) or in response to chronic poisoning (of several months duration) in rabbits and monkeys (18,19). In contrast to the autoradiography results, however, the MRI studies failed to report any signal enhancement in structures such as the olfactory bulb or hippocampal formation. Most likely, however, this observation can be ascribed to the limited spatial resolution available and ...

Manganese‐enhanced magnetic resonance imaging (MEMRI): methodological and practical considerations

“…2,[15][16][17] In these studies, either a subcutaneous injection of a low dose (20 mg/kg) 17 or intraperitoneal, intravenous or subcutaneous injection of high doses (175 mg/kg) were used. 2,15 We have recently performed a study to address the contrast in the brain as a function of administered dose of MnCl 2 .…”

“…The third use of MEMRI has been as a whole-brain contrast agent after systemic administration. 2,[15][16][17] It has been demonstrated in mice and rats that an intraperitoneal, intravenous or subcutaneous injection of MnCl 2 leads to unique MRI contrast of the brain. 1,2,[15][16][17] Taken together, MEMRI is proving useful as a new molecular imaging method to visualize functional neural circuits and anatomy in the brain in vivo.…”

Current status of functional MRI on small animals: application to physiology, pathophysiology, and cognition

“…The precise transporter(s) for Mn 2þ into astrocytes is unknown; however, it has been suggested that transferrin receptor and/or bivalent metal transporter proteins may be important. As a consequence, areas of high astrocyte density, which display higher influx rates of Mn 2þ , could account for the differential neuroanatomical contrast resulting from systemic Mn 2þ injections (73,75). However, this correlation did not always seem valid (76).…”

New developments in magnetic resonance imaging of the brain

“…Preliminary analysis of high-resolution images of the rat and mouse indicate that a number of features of neuroarchitecture can be detected, including cortical and olfactory bulb layers, the granule cells of the dentate gyrus and CA formation of the hippocampus, and the three cell layers of the cerebellum. 52,53 The molecular mechanism for why Mn 2ϩ accumulates specifically in a manner that gives such useful contrast is not clear; however, it may be reporting on cell density. If so, Mn 2ϩ will be useful for characterizing a number of pathological conditions that are known to cause changes in cell numbers in specific areas of the brain.…”