Pediatric Cardiology Fellowship Standards for Training in Exercise Medicine and Curriculum Outline.

Over the past 2 decades, fundamentals of exercise medicine, including clinical exercise testing, assessment and promotion of physical activity, exercise prescription, and supervised exercise training/rehabilitation programming have demonstrated considerable clinical value in the management of children and adolescents with congenital and acquired heart disease. Although the principles of exercise medicine have become an integral component in pediatric cardiology, there are no standardized training recommendations for exercise physiology during pediatric cardiology fellowship at this time. Thus, the Pediatric Cardiology Exercise Medicine Curriculum Committee (PCEMCC) was formed to establish core and advanced exercise physiology training recommendations for pediatric cardiology trainees. The PCEMCC includes a diverse group of pediatric cardiologists, exercise physiologists, and fellowship program directors. The expert consensus training recommendations are by no means a mandate and are summarized herein, including suggestions for achieving the minimum knowledge and training needed for general pediatric cardiology practice.

Cardiopulmonary Exercise Performance in the Pediatric and Young Adult Population Before and During the COVID-19 Pandemic.

Physical activity (PA) decreased and sedentary behavior (SB) increased in the pediatric population during the Coronavirus Disease 2019 (COVID-19) pandemic. We examined the effects of PA and SB on cardiopulmonary exercise performance in children, adolescents and young adults both with and without underling cardiac disease, and hypothesized that there will be a change in aerobic and physical working capacity during the pandemic. This was a single-center retrospective longitudinal cohort study in patients age 6-22 years who underwent serial maximal cardiopulmonary exercise stress testing before and during the COVID-19 pandemic. Metabolic variables were obtained; PA and SB data were extracted from clinic notes. A total of 122 patients (60% male) underwent serial exercise testing with a median age of 14 years at the first CPET. Predicted peak aerobic capacity significantly decreased among both females and males during the pandemic, even after adjusting for changes in somatic growth. There was no significant change in physical working capacity during the pandemic. Patients who were more aerobically fit experienced a greater decrease in aerobic capacity during the pandemic compared to those less fit. In conclusion, cardiopulmonary exercise performance, notably aerobic activity, decreased during the COVID-19 pandemic in children, adolescents and young adults compared to pre-pandemic values. This decline was most notable in those with the highest pre-pandemic aerobic capacity values and was independent of somatic growth or changes in BMI. This study has public health implications and demonstrates the importance of PA on overall cardiovascular health.

Change in knee osteoarthritis cartilage detected by delayed gadolinium enhanced magnetic resonance imaging following treatment with collagen hydrolysate: a pilot randomized controlled trial.

OBJECTIVE: To determine whether either of two magnetic resonance imaging approaches - delayed gadolinium enhanced magnetic resonance imaging of cartilage (dGEMRIC), or T2 mapping - can detect short-term changes in knee hyaline cartilage among individuals taking a formulation of collagen hydrolysate. DESIGN: Single center, prospective, randomized, placebo-controlled, double-blind, pilot trial of collagen hydrolysate for mild knee osteoarthritis (OA). Participants were allowed to continue the prior analgesic use. The primary outcome was change in dGEMRIC T1 relaxation time in the cartilage regions of interest at the 24-week timepoint. Secondary endpoints included the change in dGEMRIC T1 relaxation time between baseline and 48 weeks, the change in T2 relaxation time at 0, 24 and 48 weeks, the symptom and functional measures obtained at each of the visits, and overall analgesic use. RESULTS: Among a sample of 30 randomized subjects the dGEMRIC score increased in the medial and lateral tibial regions of interest (median increase of 29 and 41 ms respectively) in participants assigned to collagen hydrolysate but decreased (median decline 37 and 36 ms respectively) in the placebo arm with the changes between the two groups at 24 weeks reaching significance. No other significant changes between the two groups were seen in the other four regions, or in any of the T2 values or in the clinical outcomes. CONCLUSIONS: These preliminary results suggest that the dGEMRIC technique may be able to detect change in proteoglycan content in knee cartilage among individuals taking collagen hydrolysate after 24 weeks.

The influence of mechanical Circulatory support on post-transplant outcomes in pediatric patients: A multicenter study from the International Society for Heart and Lung Transplantation (ISHLT) Registry.

BACKGROUND: Mechanical circulatory support (MCS) is increasingly being used as a bridge to transplant in pediatric patients. We compare outcomes in pediatric patients bridged to transplant with MCS from an international cohort. METHODS: This retrospective cohort study of heart-transplant patients reported to the International Society for Heart and Lung Transplantation (ISHLT) registry from 2005-2017 includes 5,095 patients <18 years. Pretransplant MCS exposure and anatomic diagnosis were derived. Outcomes included mortality, renal failure, and stroke. RESULTS: 26% of patients received MCS prior to transplant: 240 (4.7%) on extracorporeal membrane oxygenation (ECMO), 1,030 (20.2%) on ventricular assist device (VAD), and 54 (1%) both. 29% of patients were <1 year, and 43.8% had congenital heart disease (CHD). After adjusting for clinical characteristics, compared to no-MCS and VAD, ECMO had higher mortality during their transplant hospitalization [OR 3.97 & 2.55; 95% CI 2.43-6.49 & 1.42-4.60] while VAD mortality was similar [OR 1.55; CI 0.99-2.45]. Outcomes of ECMO+VAD were similar to ECMO alone, including increased mortality during transplant hospitalization compared to no-MCS [OR 4.74; CI 1.81-12.36]. Patients with CHD on ECMO had increased 1 year, and 10 year mortality [HR 2.36; CI 1.65-3.39], [HR 1.82; CI 1.33-2.49]; there was no difference in survival in dilated cardiomyopathy (DCM) patients based on pretransplant MCS status. CONCLUSION: Survival in CHD and DCM is similar in patients with no MCS or VAD prior to transplant, while pretransplant ECMO use is strongly associated with mortality after transplant particularly in children with CHD. In children with DCM, long term survival was equivalent regardless of MCS status.

"Why aren't we there yet?" Re-examining standard paradigms in imaging of OA: summary of the 2nd annual workshop on imaging based measures of osteoarthritis.

OBJECTIVE: This white paper constitutes an overview of presentations and discussions from the 2nd annual osteoarthritis (OA) imaging workshop. DESIGN: This workshop brought together the communities of basic OA researchers, orthopedists and rheumatologists, imaging scientists, instrument manufacturers, and pharmaceutical and regulatory representatives to try to identify those factors that have limited imaging [focusing mostly on magnetic resonance imaging (MRI)] from making larger inroads into understanding and treating OA ("why aren't we there yet"), and to delineate future directions for success. RESULTS: The meeting was successful in raising awareness and questions about how we may proceed in this process. There was a general consensus that a change in direction is needed for OA imaging research to succeed in yielding a better understanding of OA and development of preventive and therapeutic procedures. CONCLUSIONS: Our current paradigms are limiting the potential for MRI, by limiting how trials are designed and interpreted. Many basic questions remain in biology, pathophysiology, pain, and biomechanics; these questions need to be identified and specific imaging protocols need to be developed to address them. The OA research communities need to work alongside the regulatory, pharmaceutical, and MRI industries to support the new ideas and engage in the positive reinforcement of resources to further the new studies.

Lithium ion inhibits nerve growth factor-induced neurite outgrowth and phosphorylation of nerve growth factor-modulated microtubule-associated proteins.

LiCl (2.5-20 mM) reversibly suppressed nerve growth factor (NGF)-induced neurite outgrowth by cultured rat PC 12 pheochromocytoma cells. Similar concentrations of LiCl also reversibly blocked NGF-dependent regeneration of neurites by PC12 cells that had been primed by long-term pre-exposure to NGF and by cultured newborn mouse sympathetic neurons. In contrast, transcription-dependent responses of PC12 cells to NGF such as priming and induction of the NGF-inducible large external glycoprotein, occurred despite the presence of Li+. SDS PAGE analysis of total cellular phosphoproteins (labeled by 2-h exposure to 32P-orthophosphate) from neurite-bearing primed PC12 cells revealed that Li+ reversibly inhibited the phosphorylation of a band of Mr 64,000 that was barely detectable in NGF-untreated PC12 cells. However, Li+ did not appear to affect the labeling of other phosphoproteins in either NGF-primed or untreated PC12 cultures, nor did it affect the rapid increase in phosphorylation of several proteins that occurs when NGF is first added to unprimed cultures. Several criteria indicated that the NGF-inducible phosphoprotein of Mr 64,000 is a microtubule-associated protein (MAP). Of the NGF-inducible phosphorylated MAPs that have been detected in PC12 cells (Mr 64,000, 72,000, 80,000, and 320,000), several (Mr 64,000, 72,000, and 80,000) were found to be substantially less phosphorylated in the presence of Li+. Neither a phorbol ester tumor promotor nor permeant cAMP analogs reversed the inhibitory effects of Li+ on neurite outgrowth or on phosphorylation of the component of Mr 64,000. Microtubules are a major and required constituent of neurites, and MAPs may regulate the assembly and stability of neuritic microtubules. The observation that Li+ selectively inhibits NGF-induced neurite outgrowth and MAP phosphorylation suggests a possible causal relationship between these two events.

Precision of 3.0 Tesla quantitative magnetic resonance imaging of cartilage morphology in a multicentre clinical trial.

OBJECTIVE: Quantitative MRI (qMRI) of cartilage morphology is a promising tool for disease-modifying osteoarthritis drug (DMOAD) development. Recent studies at single sites have indicated that measurements at 3.0 Tesla (T) are more reproducible (precise) than those at 1.5 T. Precision errors and stability in multicentre studies with imaging equipment from various vendors have, however, not yet been evaluated. METHODS: A total of 158 female participants (97 Kellgren and Lawrence grade (KLG) 0, 31 KLG 2 and 30 KLG 3) were imaged at 7 clinical centres using Siemens Magnetom Trio and GE Signa Excite magnets. Double oblique coronal acquisitions were obtained at baseline and at 3 months, using water excitation spoiled gradient echo sequences (1.0x0.31x0.31 mm3 resolution). Segmentation of femorotibial cartilage morphology was performed using proprietary software (Chondrometrics GmbH, Ainring, Germany). RESULTS: The precision error (root mean square coefficient of variation (RMS CV)%) for cartilage thickness/volume measurements ranged from 2.1%/2.4% (medial tibia) to 2.9%/3.3% (lateral weight-bearing femoral condyle) across all participants. No significant differences in precision errors were observed between KLGs, imaging sites, or scanner manufacturers/types. Mean differences between baseline and 3 months ranged from <0.1% (non-significant) in the medial to 0.94% (p<0.01) in the lateral femorotibial compartment, and were 0.33% (p<0.02) for the total femorotibial subchondral bone area. CONCLUSIONS: qMRI performed at 3.0 T provides highly reproducible measurements of cartilage morphology in multicentre clinical trials with equipment from different vendors. The technology thus appears sufficiently robust to be recommended for large-scale multicentre trials.

Oncogene N-ras mediates selective inhibition of c-fos induction by nerve growth factor and basic fibroblast growth factor in a PC12 cell line.

A cell line was generated from U7 cells (a subline of PC12 rat pheochromocytoma cells) that contains a stably integrated transforming mouse N-ras (Lys-61) gene under the control of the long terminal repeat from mouse mammary tumor virus. Such cells, designated UR61, undergo neuronal differentiation upon exposure to nanomolar concentrations of dexamethasone, as a consequence of expression of the activated N-ras gene (I. Guerrero, A. Pellicer, and D.E. Burstein, Biochem, Biophys. Res. Commun. 150:1185-1192, 1988). Exposure of UR61 cells to either nerve growth factor (NGF) or basic fibroblast growth factor (bFGF) results in a marked induction of c-fos RNA, with kinetics paralleling those of NGF- or bFGF-induced expression of c-fos RNA in PC12 cells. Dexamethasone-induced expression of activated N-ras p21 results in blocking of c-fos RNA induction by NGF or bFGF in a time-dependent manner. Activated N-ras p21-mediated inhibition of c-fos RNA induction in UR61 cells is selective for NGF and bFGF and is not due to selective degradation of c-fos RNA. Normal and transforming N-ras can trans activate the chloramphenicol acetyltransferase gene linked to mouse c-fos regulatory sequences when transient expression assays are performed. Our observations suggest that N-ras p21 selectively interacts with pathways involved in induction of c-fos expression which initiate at the receptors for NGF and bFGF.

Regulation of protein kinase C activity in neuronal differentiation induced by the N-ras oncogene in PC-12 cells.

Expression of the N-ras oncogene under the control of the glucocorticoid-responsive promoter in the pheochromocytoma cell line UR61, a subline of PC-12 cells, has been used to investigate the differentiation process to neuronal cells triggered by ras oncogenes (I. Guerrero, A. Pellicer, and D. E. Burstein, Biochem. Biophys. Res. Commun. 150:1185-1192, 1988). Using ras-inducible cell lines, we observed that expression of the oncogenic N-ras p21 protein interferes with the ability of phorbol esters to induce downregulation of protein kinase C. This effect was associated with the appearance of immunologically detectable protein kinase C as well as the activity of the enzyme as analyzed either by binding of [3H]phorbol-12,13-dibutyrate in intact cells or by in vitro kinase activity. These results indicate a relationship between ras p21 and protein kinase C in neuronal differentiation in this model system. Comparison to the murine fibroblast system suggests that this relationship may be functional.

Immunohistochemical localization of basic fibroblast growth factor in astrocytomas.

Because of the prominent neovascularization observed in the growth of brain tumors, we studied the occurrence of basic fibroblast growth factor (bFGF), a potent angiogenic factor in astrocytomas, the most aggressive of which often have marked vascular hyperplasia. Using immunohistochemical methods, we examined 21 examples of such tumors, 7 glioblastomas multiforme, 7 anaplastic astrocytomas, and 7 low grade astrocytomas. Using polyclonal and affinity-purified rabbit antisera to human bFGF, we detected immunoreactive bFGF in all cases of glioblastoma multiforme. bFGF was present in both endothelial cells and neoplastic astrocytes. In 4 of 7 anaplastic astrocytomas, the tumor astrocytes had bFGF immunoreactivity and, in 5 of 7 cases, endothelial cells were also immunopositive. In glioblastomas multiforme and anaplastic astrocytomas, capillaries adjacent to tumor showed bFGF immunoreactivity, whereas capillaries distant from the tumors were not immunostained. In low grade astrocytomas, astrocytic cells were weakly immunoreactive in 2 of 7 cases, and in only 1 of the 7 cases capillaries were immunostained. In each grade, reactive astroglial cells showed variable bFGF immunoreactivity. The immunostaining was not seen with the flow-through fraction obtained after affinity purification of the bFGF antiserum with pure recombinant bFGF. These results suggest a possible role for bFGF in tumor growth and in angiogenesis in astrocytomas.

Prevention of diabetes in BB/Wor rat by single transfusion of spleen cells. Parameters that affect degree of protection.

Previous studies have shown that multiple transfusions of spleen cells from histocompatible nondiabetic donors prevent autoimmune diabetes mellitus in diabetes-prone (DP) BioBreeding/Worcester (BB/Wor) rats. In this study, a single transfusion of greater than or equal to 50 x 10(6) cells from either diabetes-resistant (DR) BB/Wor or Wistar-Furth (WF) rats substantially reduced the incidence of diabetes when given to DP rats 27 or 46 days old but not 61 days old. Transfusion and protection were associated with the appearance of RT6+ donor lymph node cells in recipient rats. In vivo depletion of RT6+ T-lymphocytes in 150-day-old protected animals did not produce diabetes. DR BB/Wor and WF spleen cells were equally efficacious when given either intraperitoneally or intravenously. Mitogen-activated spleen cells were relatively less effective than untreated cells. We conclude that BB rat diabetes can be prevented by one transfusion of spleen cells from histocompatible DR and WF donors, and that the protective effect is dependent on recipient age and cell dose. The effect may be mediated by a population of RT6+ T-lymphocytes that, during a critical developmental period, regulate the expression of autoimmunity in these animals.

Parvovirus B19-associated hemophagocytic syndrome.

Parvovirus B19 is a recently described pathogen, associated with an increasing spectrum of clinical manifestations. We present the first reported case, to our knowledge, of parvovirus B19-associated hemophagocytic syndrome, in which the diagnosis of parvovirus infection was documented by the presence of B19-specific IgM and IgG antibodies. Pancytopenia resolved immediately following splenectomy and the patient recovered completely.

Changes in efferent and afferent connectivity in rats with induced cerebrocortical microgyria.

Freezing injury to the cortical plate at postnatal day (P) 1 initiates a cascade of events that ultimately result in a focal neocortical malformation resembling human 4-layered microgyria. This malformation has been associated with widespread changes in neocortical and thalamic architecture and physiology. It was hypothesized that at least some of these alterations could result from connectional reorganization following early injury. The current experiment was designed to delineate the efferent and afferent connections between the cerebral hemispheres and between the cortex and thalamus of rats with induced cerebrocortical microgyria. Microgyria were induced in the parietal cortex of rats by freezing injury on postnatal day 1. In adulthood, injections of biotinylated dextran amine were made either in the microgyric cortex, in homologous regions of the opposite hemisphere, or in ipsilateral ventrobasal complex of the thalamus. Appropriately directed connections to homotopic areas were seen in some but not all microgyric rats. In addition, heterotopic projections to frontal and secondary sensorimotor cortices were noted. Projections from homotopic regions in the hemisphere opposite to the malformation terminated most often in the medial portions of the microgyrus or avoided it entirely. There were almost no thalamocortical or corticothalamic projections between the ventrobasal complex and the microgyrus itself, although a dense plexus of thalamocortical fibers was often noted at the border between the malformed and normal cortex. These connectional changes may help explain disturbances in architecture, physiology, and behavior associated with these focal malformations.

Posttransplantation plasmacytic proliferations related to Kaposi's sarcoma-associated herpesvirus.

Kaposi's sarcoma-associated herpesvirus (KSHV), which was originally detected in Kaposi's sarcoma, also has been found in primary effusion lymphomas (PELs) and some cases of multicentric Castleman's disease. We describe two transplant recipients who developed Kaposi's sarcoma and a spectrum of non-neoplastic lymphoproliferative disorders that show pronounced plasmacytic and plasmacytoid features. The first patient had recurrent pleural effusions and Castleman's disease-like changes in lymph nodes. The second patient had systemic lymphadenopathy and hepatosplenomegaly secondary to diffuse infiltration by polyclonal plasma cells and plasmacytoid B lymphocytes that clinically mimicked Epstein-Barr virus (EBV)-associated posttransplant lymphoproliferative disease. In both cases, KSHV DNA was detected by polymerase chain reaction and Southern blotting, and KSHV vIL-6 protein expression was identified in affected tissues by immunohistochemical localization. In contrast, no evidence of KSHV coinfection was detected in any of 31 EBV-related posttransplant lymphoproliferative disorders or 112 non-PEL lymphomas tested. The pathologic findings in these two patients were not representative of malignancy by morphologic, immunophenotypic, or molecular criteria. This study underscores the marked propensity for hematolymphoid proliferations associated with KSHV infections to show plasmacytic features. Additionally, this study describes use of an antibody reactive against KSHV vIL-6 that can readily detect a subpopulation of KSHV-infected hematopoietic cells.

Synaptophysin: a sensitive and specific marker for ganglion cells in central nervous system neoplasms.

Synaptophysin, a 38-kilodalton glycoprotein found in synaptic vesicle membranes, has been shown to be a sensitive marker of neuroendocrine differentiation in non-central nervous system (CNS) tumors. We analyzed the patterns of synaptophysin immunoreactivity in CNS neoplasms in comparison with various normal CNS sites in biopsies. Normal gray matter structures all showed a diffuse punctate granular pattern of neuropil staining without staining of neuronal cell bodies. In contrast, neoplastic ganglion cells in 18 of 18 gangliogliomas/gangliocytomas showed intense immunoreactivity outlining the borders of the cell bodies. Focal staining was also seen in five of 16 primitive neuroectodermal tumors and in one of three central neurocytomas, but these tumors had a finely granular neuropil pattern of immunoreactivity more like that of normal gray matter than like that of the gangliogliomas. All 35 examples of pure gliomas of various types showed no immunoreactivity. Our data highlight synaptophysin as a sensitive and specific marker of both neuronal lineage and neoplastic character in gangliogliomas.

Synaptophysin: a sensitive and specific marker for ganglion cells in central nervous system neoplasms.

Synaptophysin, a 38-kilodalton glycoprotein found in synaptic vesicle membranes, has been shown to be a sensitive marker of neuroendocrine differentiation in non-central nervous system (CNS) tumors. We analyzed the patterns of synaptophysin immunoreactivity in CNS neoplasms in comparison with various normal CNS sites in biopsies. Normal gray matter structures all showed a diffuse punctate granular pattern of neuropil staining without staining of neuronal cell bodies. In contrast, neoplastic ganglion cells in 18 of 18 gangliogliomas/gangliocytomas showed intense immunoreactivity outlinging the borders of the cell bodies. Focal staining was also seen in five of 16 primitive neuroectodermal tumors and in one of three central neurocytomas, but these tumors had a finely granular neuropil pattern of immunoreactivity more like that of normal gray matter than like that of the gangliogliomas. All 35 examples of pure gliomas of various types showed no immunoreactivity. Our data highlight synaptophysin as a sensitive and specific marker of both neuronal lineage and neoplastic character in gangliogliomas.

MRI techniques in early stages of cartilage disease.

Cartilage degenerative diseases affect millions of people. Our understanding of these diseases and our ability to establish efficacious treatment strategies have been confounded by the difficulty of nondestructively evaluating the state of cartilage. Imaging strategies that allow visualization of cartilage integrity would revolutionize the field by allowing us to visualize early stages of degeneration and thus to evaluate predisposing factors for cartilage disease and changes resulting from interventions (eg, therapies) in culture studies, tissue-engineered systems, animal models, and in vivo in humans. Here we briefly review current state-of-the-art MRI strategies relevant to understanding and following treatment in early cartilage degeneration. We review MRI as applied to the assessment of the whole joint, of cartilage as a whole (as an organ), of cartilage tissue, and of cartilage molecular composition and structure. Each of these levels is amenable to assessment by MRI and offers different information that, in the long run, will serve as an important element of cartilage imaging.

Magnetic resonance imaging of relative glycosaminoglycan distribution in patients with autologous chondrocyte transplants.

RATIONALE AND OBJECTIVES: Autologous chondrocyte transplantation (ACT) is a potential treatment for full-thickness chondral lesions in the knee. Delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) has recently been developed as a sensitive and specific measure of cartilage glycosaminoglycans (GAGs). Under the conditions of dGEMRIC, T1 is directly related to the GAG concentration. Our aim for this study was to demonstrate the potential of dGEMRIC to evaluate ACT implants. METHODS: Eleven ACT implants were studied 2 to 24 months postoperatively by dGEMRIC. T1 values from three regions of interest were obtained to examine GAG content (1) in the implant, (2) in native cartilage adjacent to the implant, and (3) in native cartilage further removed from the implant (as "control"). RESULTS: One implant failed and therefore was not included. Four of the implants were studied between 2 and 6 months postoperatively and showed low T1 (GAG), less than 80% of the control native cartilage. Five of the six implants studied between 12 and 24 months postoperativley showed T1 (GAG) comparable to (>80%) of control. One 18-month graft showed low T1 comparable to the surrounding native cartilage, with normal GAG seen in cartilage far from the graft site. The GAG index (T1 values of the graft normalized to control) from the group of implants 6 months or less was 59% +/- 5% of control, whereas those at 12 to 24 months were 91% +/- 18% of control. The two groups were statistically different with a P value of 0.005. CONCLUSIONS: The GAG level in grafts that were implanted for less than 12 months appeared to be lower than that in the remote cartilage. At 12 months or greater, the grafts in this study had GAG levels that were comparable to both the adjacent and remote cartilage. This preliminary study of ACT implants has shown that it is feasible to apply the dGEMRIC technique in patients with ACT as a way to obtain information related to the composition of grafts. These results provide motivation and the pilot data with which to design further clinical studies.

MRI visualization of focal induced neocortical malformations of the rat.

In an attempt to determine whether small focal malformations of the neocortex can be visualized in vivo, focal microgyria were induced in the neocortex of otherwise normal rats by freezing injury to the developing cortical plate, and in adulthood the malformation was visualized using MRI. Induced microgyria of varying size were successfully visualized with MRI, and the location and extent of the malformation was confirmed on subsequent histology. This work has potential implications for the field of experimental neuropathology by enhancing the ability to study the behavioral and connectional consequences of these malformations in animals. In addition, this work points toward future research for the in vivo visualization of these small, focal malformations in humans.

In vivo microelectrode track reconstruction using magnetic resonance imaging.

To obtain more precise anatomical information about cortical sites of microelectrode recording and microstimulation experiments in alert animals, we have developed a non-invasive, magnetic resonance imaging (MRI) technique for reconstructing microelectrode tracks. We made microelectrode penetrations in the brains of anesthetized rats and marked sites along them by depositing metal, presumably iron, with anodic monophasic or biphasic current from the tip of a stainless steel microelectrode. The metal deposits were clearly visible in the living animal as approximately 200 microm wide hypointense punctate marks using gradient echo sequences in a 4.7T MRI scanner. We confirmed the MRI findings by comparing them directly to the postmortem histology in which the iron in the deposits could be rendered visible with a Prussian blue reaction. MRI-visible marks could be created using currents as low as 1 microA (anodic) for 5 s, and they remained stable in the brains of living rats for up to nine months. We were able to make marks using either direct current or biphasic current pulses. Biphasic pulses caused less tissue damage and were similar to those used by many laboratories for functional microstimulation studies in the brains of alert monkeys.