Longitudinal in vivo magnetic resonance imaging studies in experimental allergic encephalomyelitis: effect of a neurotrophic treatment on cortical lesion development

Methods for Testing Immunological Factors

Hypersensitivity reactions can be elicited by various factors: either immunologically induced, i.e., allergic reactions to natural or synthetic compounds mediated by IgE, or non-immunologically induced, i.e., activation of mediator release from cells through direct contact, without the induction of, or the mediation through immune responses. Mediators responsible for hypersensitivity reactions are released from mast cells. An important preformed mediator of allergic reactions found in these cells is histamine. Specific allergens or the calcium ionophore 48/80 induce release of histamine from mast cells. The histamine concentration can be determined with the o-phthalaldehyde reaction.

Using magnetic resonance imaging in animal models to guide drug development in multiple sclerosis

Major advances are taking place in the development of therapeutics for multiple sclerosis (MS), with a move past traditional immunomodulatory/immunosuppressive therapies toward medications aimed at promoting remyelination or neuroprotection. With an increase in diversity of MS therapies comes the need to assess the effectiveness of such therapies. Magnetic resonance imaging (MRI) is one of the main tools used to evaluate the effectiveness of MS therapeutics in clinical trials. As all new therapeutics for MS are tested in animal models first, it is logical that MRI be incorporated into preclinical studies assessing therapeutics. Here, we review key papers showing how MR imaging has been combined with a range of animal models to evaluate potential therapeutics for MS. We also advise on how to maximize the potential for incorporating MRI into preclinical studies evaluating possible therapeutics for MS, which should improve the likelihood of discovering new medications for the condition.

Neuroimaging of demyelination and remyelination models

Small-animal magnetic resonance imaging is becoming an increasingly utilized noninvasive tool in the study of animal models of MS including the most commonly used autoimmune, viral, and toxic models. Because most MS models are induced in rodents with brains and spinal cords of a smaller magnitude than humans, small-animal MRI must accomplish much higher resolution acquisition in order to generate useful data. In this review, we discuss key aspects and important differences between high field strength experimental and human MRI. We describe the role of conventional imaging sequences including T1, T2, and proton density-weighted imaging, and we discuss the studies aimed at analyzing blood-brain barrier (BBB) permeability and acute inflammation utilizing gadolinium-enhanced MRI. Advanced MRI methods, including diffusion-weighted and magnetization transfer imaging in monitoring demyelination, axonal damage, and remyelination, and studies utilizing in vivo T1 and T2 relaxometry, provide insight into the pathology of demyelinating diseases at previously unprecedented details. The technical challenges of small voxel in vivo MR spectroscopy and the biologically relevant information obtained by analysis of MR spectra in demyelinating models is also discussed. Novel cell-specific and molecular imaging techniques are becoming more readily available in the study of experimental MS models. As a growing number of tissue restorative and remyelinating strategies emerge in the coming years, noninvasive monitoring of remyelination will be an important challenge in small-animal imaging. High field strength small-animal experimental MRI will continue to evolve and interact with the development of new human MR imaging and experimental NMR techniques.

Improved detectability of experimental allergic encephalomyelitis in excised swine spinal cords by high b-value q-space DWI

Experimental allergic encephalomyelitis (EAE) is the primary experimental model of multiple sclerosis (MS), which involves both inflammation and demyelination and is known to be species-dependent. Spinal cord abnormalities were found in more than 80% of postmortem specimens of MS patients. In the present study, T1, T2 and high b-value q-space diffusion-weighted magnetic resonance imaging (MRI) were used, for the first time, to characterize the EAE model in excised swine spinal cords. The MR images were compared with histological staining and clinical scoring. Although all spinal cords were excised from swine with severe or very severe (clinical score between 3 to 5 on a scale of 5) motor impairments, T1- and T2-weighted MRI revealed white matter (WM) abnormalities in only five of the ten EAE diseased spinal cords studied, while high b-value q-space diffusion weighted MRI (q-space DWI) detected WM abnormalities in all diseased spinal cords studied. Interestingly, high b-value q-space DWI was able to detect abnormalities in the normal appearing white matter (NAWM) even in spinal cords where no plaques were identified by the T1- and T2-weighted MR images. Good anatomical correlation was observed between the high b-value q-space MR images and histology. The extent of DWI abnormalities paralleled the clinical scoring and correlated with histology. In addition, areas classified as NAWM by the T1- and T2-weighted MR images that showed abnormalities in the q-space DWI were also found to have abnormal histology. This improved detection level of the EAE model by high b-value q-space DWI over conventional T1-, and T2-weighted MRI is briefly discussed.

Pathology-guided MR analysis of acute and chronic experimental allergic encephalomyelitis spinal cord lesions at 1.5T

PURPOSE

To directly correlate spinal cord pathology of guinea pigs with experimental allergic encephalomyelitis (EAE) to the MRI data obtained at 1.5T.

MATERIALS AND METHODS

Spinal cords from EAE animals were imaged in vivo with the following MRI sequences: T2-FSE, PD-FSE, fluid-attenuated inversion recovery (FLAIR)-FSE, T2-CSE, T1-CSE, T1-CSE + gadolinium-DTPA (Gd-DTPA), PD-CSE, and short-tau inversion recovery (STIR)-FSE. The spinal cords were removed and the lesions with specific pathological compositions were identified by histological analysis. Regions of interest (ROIs) were drawn on the corresponding MR images, and signal-to-noise ratios (SNRs) were measured for each MR sequence and compared with controls.

RESULTS

The receiver operating characteristic (ROC) analysis of STIR-FSE and PD-CSE was able to differentiate tissue that contained cellular infiltrates with a high degree of accuracy. The SNRs of T2-FSE, STIR-FSE, T2-CSE, PD-CSE, and T1-CSE + Gd-DTPA were elevated in lesions that contained cellular infiltrates alone, whereas the SNRs of PD-CSE and T1-CSE + Gd-DTPA were reduced in demyelinated lesions that also contained inflammation.

CONCLUSION

The SNR difference between the two lesion groups suggests that the combination of STIR-FSE, PD-CSE, and T1-CSE + Gd-DTPA sequences may be useful for differentiating inflammatory lesions containing demyelination from lesions with inflammation alone.

Neuroimaging of animal models of brain disease

The main aim of this review is to describe some of the many animal models that have proved to be valuable from a neuroimaging perspective. This paper complements other articles in this volume, with a focus on animal models of the pathology of human brain disorders for investigations with modern non-invasive neuroimaging techniques. The use of animal model systems forms a fundamental part of neuroscience research efforts to improve the prevention, diagnosis, understanding and treatment of neurological conditions. Without such models it would be impossible to investigate such topics as the underlying mechanisms of neuronal cell damage and death, or to screen compounds for possible anticonvulsant properties. The adequacy of any one particular model depends on the suitability of information gained during experimental conditions. It is important, therefore, to understand the various types of animal model available and choose an appropriate model for the research question.

Magnetization transfer and multicomponent T2 relaxation measurements with histopathologic correlation in an experimental model of MS

Magnetization transfer and multicomponent T2 imaging techniques were implemented to study guinea pig in vivo. A chronic-progressive model of experimental allergic encephalomyelitis (EAE) was produced, and the inflammatory component of the disease was manipulated using antibodies against integrin. The magnetization transfer ratio (MTR) and T2 relaxation properties were measured in normal-appearing white matter (NAWM) with histological comparisons. Significant reductions in both the mean MTR and the myelin water percentage were measured in NAWM of EAE guinea pig brain. However, the MTR and myelin water percentage appear to measure different aspects of pathology in NAWM in EAE. Reductions in the MTR were prevented or reversed with suppression of inflammation. However, modulation of inflammatory activity was not reflected in the measurement of the myelin water percentage. Since the amount of myelin is not expected to vary with inflammatory-related changes, these observations support our hypothesis that the MTR is sensitive to physiological changes to myelin induced by inflammation, while the short T2 component is a more specific indicator of myelin content in tissue. Pathologic features other than demyelination may be important in the determination of the MTR.

Further evidence for a role of nitric oxide in experimental allergic encephalomyelitis: aminoguanidine treatment modifies its clinical evolution

The role of nitric oxide (NO) in inflammatory/demyelinating diseases is undergoing extensive investigation as a potential target for therapeutic intervention. However, interference with NO production has resulted in contrasting effects on the development of experimental allergic encephalomyelitis (EAE), the most widely used experimental model for multiple sclerosis (MS). Purpose of this paper was both the analysis of the individual clinical evolution of EAE induced in Lewis female rats by active immunisation and the evaluation of the effect of treatment with aminoguanidine, a selective inhibitor for the inducible isoform of nitric oxide synthase (iNOS). In our experimental model, relapse occurred in 66% of animals. Aminoguanidine treatment, started 3 days before immunisation, guaranteed a complete recovery from the acute phase and a delayed, milder relapse. Moreover, 79 days after immunisation inflammatory cellular infiltrates in the spinal cord were reduced. These data further support the involvement of NO in EAE evolution.

In vivo measurements of multi-component T2 relaxation behaviour in guinea pig brain

Multi-echo Carr-Purcell-Meiboom-Gill (CPMG) imaging sequences were implemented on 1.5 T and 4.0 T imaging systems to test their ability to measure in vivo multi-component T2 relaxation behavior in normal guinea pig brain. The known dependence of accurate T2 measurements on the signal-to-noise ratio (SNR) was explored in vivo by comparing T2 decay data obtained using three methods to increase SNR (improved RF coil design, signal averaging and increased magnetic field strength). Good agreement between T2 values of nickel-doped agarose phantoms was found between imaging and spectroscopic methods. T2 values were determined for gray matter (GM) and white matter (WM) locations from images of guinea pig brain in vivo. T2 measurements of GM were found to be monoexponential at both field strengths. The mean T2 times for GM were 71 ms at 1.5 T, and 53 ms at 4.0T. The highest average SNR was achieved using an improved RF coil at 4.0T. In this case, two peaks were extracted in WM, a "short" T2 peak at approximately 6 ms, and a "medium" T2 peak at approximately 48 ms. T2 values in GM and the major component of WM were significantly decreased at 4.0T compared to 1.5 T. The improved SNR attained with this optimized imaging protocol at 4.0T has allowed for the first time extraction of the myelin-sensitive T2 component of WM in animal brain in vivo.

Recent developments in drug therapy for multiple sclerosis

Symptomatic treatment of multiple sclerosis (MS) includes a diverse range of drugs intended to relieve the specific symptoms with which a patient may present at a particular point in the progression of the disease. These drugs, not specifically designed for the treatment of MS, may include antispastic agents (e.g. baclofen), drugs to reduce tremor (e.g. clonazepam), anticholinergics (e.g. oxybutynin) which relieve urinary symptoms, anti-epileptics (e.g. carbamazepine) to control neuralgia, stimulants to reduce fatigue (e.g. amantadine), and antidepressants (e.g. fluoxetine) to treat depression. The treatment of acute relapses or exacerbations is dominated by corticosteroids such as methylprednisolone. The most active area of current investigation is the development of drugs which will inhibit the progression of the disease process itself, and in this category the beta- and alpha-interferons are the most effective drugs currently available, although many new treatments are currently in trials, including immunoglobulin, copolymer-1. bovine myelin, T-cell receptor (TCR) peptide vaccines, platelet activating factor (PAF) antagonists, matrix metallo-proteinase inhibitors, campath-1, and insulin-like growth factor (IGF).