Boguslaw Tomanek

The aging hippocampus: a multi-level analysis in the rat.

In the current experiment we conducted a multi-level analysis of age-related characteristics in the hippocampus of young adult (3 months), middle-aged (12 months), and old (24 months) Fisher 344xBrown Norway hybrid (FBNF1) rats. We examined the relationships between aging, hippocampus, and memory using a combination of behavioral, non-invasive magnetic resonance imaging and spectroscopy, and postmortem neuroanatomical measures in the same rats. Aging was associated with functional deficits on hippocampus-dependent memory tasks, accompanied by structural alterations observed both in vivo (magnetic resonance imaging-hippocampal volume) and postmortem (dentate gyrus neuronal density and neurogenesis). Neuronal metabolic integrity, assessed by levels of N-acetylaspartate with magnetic resonance spectroscopy, was however, preserved. Further, our results suggest that neurogenesis (doublecortin) seems to be related to both performance deficits on hippocampus-dependent tasks and hippocampal volume reduction. The observed pattern of age-related alterations closely resembles that previously reported in humans and suggests FBNF1 rats to be a useful model of normal human aging.

Pilot study of dermal and subcutaneous fat structures by MRI in individuals who differ in gender, BMI, and cellulite grading

Background/aims: Puckered, dimply skin on the thighs, hips, and buttocks is known as cellulite. The cause of cellulite is not known, although there are a number of different hypotheses. In this study, we use magnetic resonance (MR) micro‐imaging to study cellulite skin. To the best of our knowledge, this is the first reported MR study of cellulite.

Adipose-derived stem cells are an effective cell candidate for treatment of heart failure: an MR imaging study of rat hearts

This study assessed the potential therapeutic efficacy of adipose-derived stem cells (ASCs) on infarcted hearts. Myocardial infarction was induced in rat hearts by occlusion of the left anterior descending artery (LAD). One week after LAD occlusion, the rats were divided into three groups and subjected to transplantation of ASCs or transplantation of cell culture medium (CCM) or remained untreated. During a 1-mo recovery period, magnetic resonance imaging showed that the ASC-treated hearts had a significantly greater left ventricular (LV) ejection fraction and LV wall thickening than did the CCM-treated and untreated hearts. The capillary density in infarct border zone was significantly higher in the ASC-treated hearts than in the CCM-treated and untreated hearts. However, only 0.5% of the ASCs recovered from the ASC-treated hearts were stained positive for cardiac-specific fibril proteins. It was also found that ASCs under a normal culture condition secreted three cardiac protective growth factors: vascular endothelial growth factor, hepatocyte growth factor, and insulin-like growth factor-1. Results of this study suggest that ASCs were able to improve cardiac function of infarcted rat hearts. Paracrine effect may be the mechanism underlying the improved cardiac function and increased capillary density.

NaDyF4 Nanoparticles as T2 Contrast Agents for Ultrahigh Field Magnetic Resonance Imaging.

A major limitation of the commonly used clinical MRI contrast agents (CAs) suitable at lower magnetic field strengths (<3.0 T) is their inefficiency at higher fields (>7 T), where next-generation MRI scanners are going. We present dysprosium nanoparticles (β-NaDyF4 NPs) as T2 CAs suitable at ultrahigh fields (9.4 T). These NPs effectively enhance T2 contrast at 9.4 T, which is 10-fold higher than the clinically used T2 CA (Resovist). Evaluation of the relaxivities at 3 and 9.4 T show that the T2 contrast enhances with an increase in NP size and field strength. Specifically, the transverse relaxivity (r2) values at 9.4 T were ∼64 times higher per NP (20.3 nm) and ∼6 times higher per Dy(3+) ion compared to that at 3 T, which is attributed to the Curie spin relaxation mechanism. These results and confirming phantom MR images demonstrate their effectiveness as T2 CAs in ultrahigh field MRIs.

Noninvasive assessment of the injured human spinal cord by means of functional magnetic resonance imaging

Study design: A magnetic resonance imaging technique that enables indirect detection of neuronal activity has been developed for the spinal cord. In the present study, this method, spinal functional magnetic resonance imaging (fMRI), is applied to the first study of the injured spinal cord, with the goal of better clinical assessment of the entire cord.Objectives: The objectives of this project are: (1) to investigate the neuronal activity that can be detected in the spinal cord caudal to a chronic injury by means of spinal fMRI, and (2) to develop spinal fMRI as a clinical diagnostic tool.Setting: Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada.Methods: fMRI of the spinal cord was carried out in 27 volunteers with cervical or thoracic spinal cord injuries (SCIs). Of these volunteers, 18 had complete injuries, and nine had incomplete injuries. Spinal fMRI was carried out in a 1.5 T clinical MR system, using established methods. Thermal stimulation at 10°C was applied to the fourth lumbar dermatome on each leg, and images were obtained of the entire lumbar spinal cord.Results: Areas of neuronal activity were consistently observed in the lumbar spinal cord in response to the thermal stimulation, even when the subjects had no awareness of the sensation. The pattern of activity was notably different compared with noninjured subjects. In general, subjects with complete SCI showed absent or diminished dorsal gray matter activity, but had enhanced ventral activity, particularly contralateral to the stimulation.Conclusions: Spinal fMRI is able to provide a noninvasive assessment of the injured spinal cord that does not depend on the patients perception of the stimulus being applied. This work was carried out on a standard clinical MRI system without modification, and so is readily applicable in most MR units.Sponsorship: This work was funded by a grant from the Canadian Institutes of Health Research (CIHR).

Mapping of neuronal function in the healthy and injured human spinal cord with spinal fMRI.

Functional magnetic resonance imaging of the human spinal cord is carried out with a graded thermal stimulus in order to establish the relationship between signal changes and neural activity. Studies of the lumbar spinal cord in 15 healthy subjects with 10 degrees C stimulation of the skin overlying the calf demonstrate a pattern of activity that matches the neuronal anatomy of the spinal cord. This pattern shows primarily dorsal horn activity, with expected components of motor reflex activity as well. Moreover, a later response shifting to noxious cold over time is also demonstrated with a shift to more dorsal horn activity. Signal intensity changes detected at different degrees of thermal stimulation have a biphasic nature, with much larger signal changes below 15 degrees C as the stimulus becomes noxious, and agree well with electrophysiological results reported in the literature. These findings demonstrate a strong correspondence between Spinal fMRI results and neural activity in the human spinal cord. Spinal fMRI is also applied to studies of the injured spinal cord, below the site of injury. Results consistently demonstrate activity in the spinal cord even when the subjects cannot feel the stimulus being applied. Signal intensity changes demonstrate the same stimulus-response pattern as that in noninjured subjects, but the areas of activity in the spinal gray matter are notably altered. In subjects with complete injuries, activity is absent ipsilateral to the thermal stimulation, but appears to be enhanced on the contralateral side. These findings demonstrate the reliability of Spinal fMRI and its clinical potential.

Extravascular proton-density changes as a non-BOLD component of contrast in fMRI of the human spinal cord.

The fractional signal intensity change (ΔS/S) observed during activation in T2‐weighted fMRI of the spinal cord has previously been shown to depend linearly on the echo time (TE) but to have a positive value of roughly 2.5% extrapolated to zero TE. In this study we investigated the origin of this finding by measuring the ΔS/S in spinal fMRI with very short TEs. Our results demonstrate that the ΔS/S does not approach zero, but has a value as high as 3.3% at TE = 11 ms. At TEs > 33 ms we observed the linear relationship between ΔS/S and TE as in previous studies. These data demonstrate that there is a non‐BOLD contribution to signal changes observed in spinal fMRI. We hypothesize that this contribution is a local proton density increase due to increased water exudation from capillaries with increased blood flow during neuronal activation, and term this effect “signal enhancement by extravascular protons” (SEEP). Magn Reson Med 48:122–127, 2002.

Correspondence of AQP4 expression and hypoxic‐ischaemic brain oedema monitored by magnetic resonance imaging in the immature and juvenile rat

Whether the water channel protein AQP4 is involved in the very early cell swelling and brain oedema observed with cerebral hypoxia–ischaemia (HI) and whether this response depends on the maturity of brain were investigated by comparing regional changes in AQP4 protein expression and signal intensity on magnetic resonance (MR) images in immature and juvenile brains. Maps of T2 and the apparent diffusion coefficient (ADC) of water were acquired in 1‐ and 4‐week‐old rats at times prior to HI, within the last 5 min of HI and 1 h or 24 h afterwards. AQP4 expression assessed with Western blotting was not significantly reduced until 24 h post‐HI irrespective of age. However, AQP4 immunostaining was decreased at the end of HI and at 1 h or 24 h after HI in the hemisphere ipsilateral to the occlusion with changes being similar in both age groups and coinciding well with regional reductions in ADC. IgG immunostaining to assess blood–brain barrier integrity and T2 were unchanged at early time points in 4‐week old rats despite decreases in AQP4 immunostaining. Thus, at early time points there were decreases in AQP4 detected with immunostaining but not Western blotting methods. However, the good correlation between alterations in ADC and AQP4 immunostaining suggests that changes in the AQP4 are involved in some of the early changes in brain water distribution observed in hypoxia‐ischemia, and supports the speculation that AQP4 is involved in the transport of water across the perivascular membranes into the vascular lumen.

MR molecular imaging of early endothelial activation in focal ischemia.

Focal ischemia followed by reperfusion initiates a harmful P‐ and E‐selectin–mediated recruitment of leukocytes in brain microvasculature. In this study, we tested whether a novel magnetic resonance (MR) contrast agent (Gd‐DTPA‐sLex A), which is designed to bind to activated endothelium could be detected by MR imaging (MRI) in a focal stroke mouse model. MRIs (9.4T) of the brain were acquired 24 hours after transient middle cerebral artery occlusion. T1 maps were acquired repeatedly before and up to 1.5 hours after the intravenous injection of either Gd‐DTPA or Gd‐DTPA‐sLex A. Analysis of images included a pixel‐by‐pixel subtraction of T1 maps from the precontrast T1 maps and quantification of T1 within the ischemic area. After injection of Gd‐DTPA‐sLex A, T1 decreased compared with precontrast levels, and an interhemispheric difference between the pre–post contrast T1 developed within the stroke lesion at a mean time of 52 minutes after injection (p < 0.05). Animals injected with Gd‐DTPA did not exhibit changes in T1 signal intensity between regions of the ipsilateral and contralateral hemispheres, indicating that the reductions in T1 observed with Gd‐DTPA‐sLex A were unrelated to blood–brain barrier breakdown. Fluorescent‐labeled sLex A administered intravenously was observed to bind to the endothelium of injured but not control brain. The study suggests that the contrast agent Gd‐DTPA‐sLex A can be used to visualize early endothelial activation after transient focal ischemia in vivo with MRI. Ann Neurol 2004;56:116–120

Functional magnetic resonance imaging of tonic pain and vasopressor effects in rats.

In functional magnetic resonance imaging (fMRI) studies, an elevation in blood pressure (BP) in individuals with a poor autoregulatory response may increase cerebral blood flow, potentially enhancing the blood oxygenation level dependent response. To investigate the role of BP changes, the cerebral activation to either tonic pain or the infusion of the vasopressor norepinephrine was correlated with the accompanying BP changes in alpha-chloralose anesthetized rats. Immediately after formalin (2%) injection into the forepaw, fMRI detected an activation that was correlated with the BP increase and additional activations that were independent of blood pressure changes 5-40 minutes later. The activation detected with the administration of the vasopressor norepinephrine, which does not cross the blood-brain barrier was correlated to both the amount and rate of increase in BP. The response ranged from being sparse, localized within cortex or widespread during modest, moderate or severe elevations in BP, respectively. The cerebral circulatory effects of hypertension should be considered as contributing to changes in cerebral blood oxygenation in fMRI studies involving increases in BP.