Amide proton transfer-weighted MRI in the clinical setting - correlation with dynamic susceptibility contrast perfusion in the post-treatment imaging of adult glioma patients at 3T.

INTRODUCTION: We investigated the correlation between amide proton transfer-weighted magnetic resonance imaging (APTw MRI) and dynamic susceptibility contrast (DSC) perfusion in order to assess the potential of APTw MRI as an alternative to DSC in adult brain tumor (glioma) imaging. METHODS: After Ethical Committee approval, forty adult patients, treated for histopathologically confirmed glioma (World Health Organization (WHO) grade II-IV), were prospectively imaged at 3 Tesla (3 T) with DSC perfusion and a commercially available three-dimensional (3D) APTw sequence. Two consultant neuroradiologists independently performed region of interest (ROI) measurements on relative cerebral blood volume (rCBV) and APTw maps, co-registered with anatomical images. The correlation APTw MRI-DSC perfusion was assessed using Spearman's rank-order test. Inter-observer agreement was evaluated by the intraclass correlation coefficient (ICC) and Bland-Altman (BA) plots. RESULTS: A statistically significant moderately strong positive correlation was observed between maximum rCBV (rCBVmax) and maximum APTw (APTwmax) values (observer 1: r = 0.73; p < 0.01; observer 2: r = 0.62; p < 0.01). We found good inter-observer agreement for APTwmax (ICC = 0.82; 95% confidence interval (CI) 0.66-0.90), with somewhat broad outer 95% CI for the BA Limits of Agreement (LoA) (-1.6 to 1.9). ICC for APTwmax was higher than ICC for rCBVmax (ICC = 0.74; 95%; CI 0.50-0.86), but the difference was not statistically significant. CONCLUSION: APTwmax values correlate positively with rCBVmax in patients treated for brain glioma. APTw imaging is a reproducible technique, with some observer dependence. Results need to be confirmed by a larger population analysis. IMPLICATIONS FOR PRACTICE: APTw MRI can be a useful addition to glioma follow-up imaging and a potential alternative to DSC perfusion, especially in patients where contrast agent is contraindicated.

Cerebral microdialysis monitoring: determination of normal and ischemic cerebral metabolisms in patients with aneurysmal subarachnoid hemorrhage.

OBJECT: The success of treatment for delayed cerebral ischemia is time dependent, and neuronal monitoring methods that can detect early subclinical levels of cerebral ischemia may improve overall treatment results. Cerebral microdialysis may represent such a method. The authors' goal was to characterize patterns of markers of energy metabolism (glucose, pyruvate, and lactate) and neuronal injury (glutamate and glycerol) in patients with subarachnoid hemorrhage (SAH), in whom ischemia was or was not suspected. METHODS: By using low-flow intracerebral microdialysis monitoring, central nervous system extracellular fluid concentrations of glucose, pyruvate, lactate, glutamate, and glycerol were determined in 46 patients suffering from poor-grade SAH. The results in two subgroups were analyzed: those patients with no clinical or radiological signs of cerebral ischemia (14 patients) and those who succumbed to brain death (five patients). Significantly lower levels of energy substrates and significantly higher levels of lactate and neuronal injury markers were observed in patients with severe and complete ischemia when compared with patients without symptoms of ischemia (glucose 0 compared with 2.12+/-0.15 mmol/L; pyruvate 0 compared with 151+/-11.5 micromol; lactate 6.57+/-1.07 compared with 3.06+/-0.32 mmol/L; glycerol 639+/-91 compared with 81.6+/-12.4 micromol; and glutamate 339+/-53.4 compared with 14+/-3.33 micromol). Immediately after catheter placement, glutamate concentrations declined over the first 4 to 6 hours to reach stable values. The remaining parameters exhibited stable values after 1 to 2 hours. CONCLUSIONS: The results confirm that intracerebral microdialysis monitoring of patients with SAH can be used to detect patterns of cerebral ischemia. The wide range from normal to severe ischemic values calls for additional studies to characterize further incomplete and possible subclinical levels of ischemia.

Expression of zinc-positive cells and terminals in fetal neocortical homografts to adult rat depends on lesion type and rearing conditions.

Zinc-positive neurons and terminals, known to be associated with the glutamatergic projections in the brain, can be demonstrated by the histochemical Timm method and later modifications thereof. The adult rat neocortex contain a uniform lamination of zinc-positive cells with specific projections to, e.g., the striatum. We have previously reported that fetal neocortical grafts implanted in the adult rat neocortex combined with rearing in an enriched environment can improve behavioral functions and reduce the secondary atrophy of thalamus after cortex infarction in adult rats. In order to examine whether the expression of zinc positivity is ontogenetically inherent to neocortical neurons we grafted fetal neocortical tissue to aspiration or ischemic lesions of the frontoparietal neocortex of adult rats, followed by histochemical visualization of the vesicular zinc pool by selenite or sulfide. One further aim of the study was to elucidate to what extent the distribution of zinc-containing neurons and terminals in the grafts depended on rearing under different environmental conditions. The foremost finding of the present study was that the overall density of zinc-containing terminals in fetal cortical transplants placed in brain infarcts of adult spontaneously hypertensive rats is higher when the rats are reared in an enriched environment. Moreover, the presence and expression of zinc-positive neurons and terminals do not seem to be ontogenetically inherent to the cortical neurons as the fetal neocortical grafts placed in aspiration lesions contained no zinc-selenide-positive neurons and few or no zinc-selenide-positive terminals. The presence or expression of zinc-positive cells may thus be induced by ingrowth of fibers and terminals from the host brain as transplants placed in the ischemic lesions expressed both zinc-positive neurons and terminals.

Corticostriatal plasticity is restricted by myelin-associated neurite growth inhibitors in the adult rat.

After unilateral cortical lesions in neonatal rats, the spared unablated hemisphere is known to demonstrate remarkable neuroanatomical plasticity in corticofugal connectivity. This same type of structural plasticity is not seen after similar lesions in adult rats. One possibility for the lack of such a plastic response in the adult central nervous system may be the presence of myelin-associated neurite growth inhibitory proteins NI-35/NI-250. These proteins have previously been found to play a crucial role in preventing axotomized fibers from regenerating after adult rat spinal cord lesions. The aim of this study was to determine if blocking these inhibitory proteins by the application of the specific monoclonal antibody IN-1 would enhance corticostriatal plasticity from the spared hemisphere after unilateral cortical lesions in adult rats. Six- to 8-week-old Lewis rats underwent unilateral aspiration lesion of the sensorimotor cortex. Animals were immediately treated with either monoclonal antibody IN-1 or a control antibody released from hybridoma cells in Millipore filter capsules. After a survival period of 12 weeks, the opposite sensorimotor cortex was stereotaxically injected with the anterograde tracer biotinylated dextran amine, and biotinylated dextran amine-positive corticostriatal fibers were analyzed. The monoclonal antibody IN-1-treated animals showed an increase in corticostriatal fibers in the dorsolateral striatum contralateral to the injection site compared with control antibody-treated animals or normal controls, indicating a specific sprouting response in the deafferented zone. These results support the idea that through blockade of myelin-associated neurite inhibitory proteins, lesion-induced corticofugal plasticity is possible even in the adult central nervous system.

Cholinergic innervation of fetal neocortical transplants is increased after neutralization of myelin-associated neurite growth inhibitors.

Fetal neocortical transplants placed into adult neocortical sensorimotor aspiration lesions are known to receive afferent input from the adult host rat brain. As this input is less dense than normal, the present study was designed to investigate whether neutralization of myelin-associated neurite growth inhibitors NI-35/250 might promote host derived cholinergic innervation of fetal neocortical transplants. Adult rats received unilateral sensorimotor cortical aspiration lesions, and block grafts from embryonic day 14-15 neocortical tissue were placed immediately into the lesion cavities. Mouse hybridoma cells secreting either the monoclonal antibody IN-1, which blocks neurite growth inhibitors NI-35/250, or a control antibody or medium without cells were applied in millipore filter capsules directly over the fetal graft tissue. The brains were processed 12 weeks later for the visualization of acetylcholinesterase-positive, presumptive cholinergic fibers. We found an enhancement in the cholinergic innervation of fetal grafts in the recipients treated with the antibody IN-1 both in terms of fibers growing into the graft and of density within the center of the grafts. These results indicate that myelin-associated neurite growth inhibitors are involved in the development of host-transplant connectivity in the adult brain.

The effect of fetal neocortical transplants on lesion-induced cerebral cortex plasticity.

Sensorimotor cortical lesions in newborn rats lead to the formation of abnormal projections from the opposite intact sensorimotor cortex. In the present study the influence of fetal neocortical transplants on this lesion-induced plasticity was examined. Newborn rats received unilateral frontal neocortical lesions. One experimental group received grafts of fetal neocortical tissue (E14-E16) into the lesion cavities. Another group served as lesion-only animals, while a third group was left unlesioned and without grafts as normal controls. At 3 mo of age, the animals received injections of the anterograde tracer biotinylated dextran amine (BDA) into the sensorimotor cortex contralateral to the lesion/transplantation area. After sacrifice 2 wk later, the brains were processed histochemically for detection of BDA-labeled cells and fibers. As a measure of the lesion-induced axonal sprouting response, corticothalamic and corticopontine fibers crossing the midline were counted. Significantly fewer cortical efferent fibers crossed the thalamic midline in the transplanted rats compared to the lesion-only controls. In contrast, the presence of transplants did not reduce the corticopontine sprouting response. These results therefore indicate that fetal neocortical grafts have a modulatory, yet variable effect on the lesion-induced axonal sprouting of contralateral sensorimotor cortical neurons.

Analysis of neocortical grafts placed into focal ischemic lesions in adult rats.

This study investigated the viability of fetal neocortical block grafts transplanted into adult ischemic cortical lesions. Recipient rats sustained focal ischemic lesions by permanent occlusion of the middle cerebral artery 4-7 days prior to transplantation. Twenty days later, the animals were sacrificed and the brains examined using triphenyltetrazolium chloride, routine Nissl or acetylcholinesterase histochemistry. Ischemic infarctions were localized to the ipsilateral sensorimotor cortex and transplants were integrated with the host cerebral cortex or striatum. Cholinergic fibers were found crossing the host-transplant interface, presumably innervating the graft. This study demonstrates that fetal neocortical block grafts placed into adult focal ischemic lesions following permanent arterial occlusion can survive and establish connections with the host brain.

Fetal neocortical transplants grafted into neocortical lesion cavities made in newborn rats: an analysis of transplant integration with the host brain.

Fetal neocortical transplants placed into frontal cortex aspiration lesion cavities in newborn rats have been shown to survive and exchange connections with the host brain. To further study the afferent innervation of such transplants, enzyme- and immunohistochemical techniques were employed to examine the distribution of cholinergic, catecholaminergic and serotonergic fibers within the transplants, and radiochemical enzyme assays and high performance liquid chromatography were used to determine the content of neurotransmitter markers for these same fiber systems. To examine functional integration of the transplanted neurons in terms of activation of molecular signaling systems, the graft recipient animals were exposed to a novel open field environment. This behavioral testing paradigm is known to induce c-fos mRNA and Fos protein within several areas of the normal brain, including the sensorimotor cortex. Subsequent detection of the induction of this particular immediate early gene (transcription as well as translation) in the grafts would gene (transcription as well as translation) in the grafts would accordingly indicate genomic activation and therefore functional integration at the level of molecular signaling systems. Our results showed that these global fiber systems are distributed evenly throughout the extent of three mo old neocortical grafts and that the content of transmitter-related markers for these systems do not differ significantly from control cortex. Open field exposure of the grafted animals resulted in c-fos mRNA and Fos protein expression of cells distributed throughout the transplants. We conclude that the "global" fiber system innervation of neocortical transplants placed into newborn rats is similar to the innervation of normal cortex and that grafted neurons respond to host brain activation at the level of molecular signaling systems.

Biochemical and anatomical analysis of cholinergic, noradrenergic and serotonergic innervation of fetal neocortical transplants placed in excitotoxin-induced neocortical lesions of adult rats.

Fetal neocortical block transplants were implanted into the excitotoxically ablated sensorimotor cortex of adult rats in order to examine the density of innervation and distribution of presumptive host derived afferent fibers within these transplants. Cholinergic fiber innervation was examined at 3 months post grafting by measuring acetylcholinesterase (AChE) and choline acetyl-transferase (ChAT) enzyme activities within the grafts and within the corresponding host cortex by radiochemical enzyme assays as well as by AChE histochemistry for the visualization of AChE positive fibers. Noradrenergic and serotonergic inputs were examined by high performance liquid chromatography (HPLC) measurements of noradrenaline (NA) and serotonin (5-hydroxytryp-tamine, 5-HT) concentrations as well as by tyrosine hydroxylase (TH) and 5-HT immunocytochemistry for the visualization of monoaminergic fiber distribution. Our results demonstrated that the grafts contained significantly lower levels of neurotransmitter markers when compared to normal unablated cortex. The anatomical analysis showed an unequal fiber distribution within the transplants. Areas adjacent to the host tissue revealed a relatively dense fiber innervation when compared to the density observed within the more central parts of the transplants, and the anatomical data therefore supported the biochemical data in suggesting an overall lower cholinergic and monoaminergic innervation of fetal neocortical transplants placed into the lesioned adult cortex when compared to normal cortex.

Expression of c-fos mRNA and c-fos protein in neocortical transplants placed into excitotoxin-induced lesions in adult rats.

Using anatomical and electrophysiological methods, previous studies from this laboratory demonstrated that fetal neocortical block transplants placed into the excitotoxically ablated cortex of adult rats can establish functional connections with the host central nervous system. In order to further examine functional integration at the level of genomic activation/molecular signaling systems, transplants were analyzed for the presence of c-fos mRNA and Fos protein-labeled cells following a 20-min exposure of the animal to a novel open-field environment. This behavioral testing paradigm, which previously was shown to induce expression of c-fos mRNA in several brain regions including the sensorimotor cortex, was administered at 3 months after grafting. The transplants were found to express c-fos mRNA as well as c-fos protein following novelty exposure. These labeled cells were distributed primarily along the peripheral margin of the grafts. This study therefore suggests that at least some neurons within transplants become integrated with the host pathways at the level of molecular signal transduction.

Connectivity of fetal neocortical block transplants in the excitotoxically ablated cortex of adult rats.

Fetal neocortical block grafts placed into newborn recipients are able to exchange axonal projections with the host central nervous system, as shown in several previous experiments. The present study examined the connectivity of fetal neocortical block transplants placed into the excitotoxically ablated cortex of adult rats. Young adult rats received injections of the excitotoxic amino acid N-methyl-D-aspartate into the sensorimotor cortex area 1 week prior to receiving a fetal (E14-15) neocortical transplant. Afferent and efferent connections of these grafts were examined 3-6 months after transplantation by injecting the transplants with the fluorescent retrograde tracers fast blue and diamidino yellow or with the anterograde tracer Phaseolus vulgaris leucoagglutinin. Retrogradely labeled neurons were observed within several host brain regions including the ipsilateral neocortex, several thalamic nuclei, subcortical areas such as claustrum and lateral hypothalamus, nucleus basalis, dorsal raphe nuclei and locus coeruleus. Fibers labeled with Phaseolus vulgaris leucoagglutinin were found extending throughout the transplants, but with rare exceptions fibers were not observed within the host brain. The experiments showed that neocortical block grafts placed into the excitotoxically ablated neocortex receive afferent input from areas in the host brain that normally innervate the sensorimotor cortex. The extensive Phaseolus vulgaris leucoagglutinin-positive axonal labeling found within the grafts demonstrated the ability of the grafted neurons to establish extensive intrinsic graft connections.(ABSTRACT TRUNCATED AT 250 WORDS)