Inhibition of neuronal FLT3 receptor tyrosine kinase alleviates peripheral neuropathic pain in mice.

Peripheral neuropathic pain (PNP) is a debilitating and intractable chronic disease, for which sensitization of somatosensory neurons present in dorsal root ganglia that project to the dorsal spinal cord is a key physiopathological process. Here, we show that hematopoietic cells present at the nerve injury site express the cytokine FL, the ligand of fms-like tyrosine kinase 3 receptor (FLT3). FLT3 activation by intra-sciatic nerve injection of FL is sufficient to produce pain hypersensitivity, activate PNP-associated gene expression and generate short-term and long-term sensitization of sensory neurons. Nerve injury-induced PNP symptoms and associated-molecular changes were strongly altered in Flt3-deficient mice or reversed after neuronal FLT3 downregulation in wild-type mice. A first-in-class FLT3 negative allosteric modulator, discovered by structure-based in silico screening, strongly reduced nerve injury-induced sensory hypersensitivity, but had no effect on nociception in non-injured animals. Collectively, our data suggest a new and specific therapeutic approach for PNP.

Early functional outcomes and histological analysis after spinal cord compression injury in rats.

OBJECT: Neuroprotective and repair strategies in spinal cord injuries (SCIs) have been so far largely unsuccessful. One of the prerequisites is the use of appropriate preclinical models to decipher pathophysiological mechanisms; another is the identification of optimal time windows for therapeutic interventions. The authors undertook this study to characterize early motor, sensory, autonomic, and histological outcomes after balloon compression of the spinal cord at the T8-9 level in adult rats. METHODS: A total of 91 rats were used in this study. Spinal cord balloon compression was performed at T8-9 in adult rats by inflation of a 2 Fr Fogarty catheter into the epidural space. The authors first characterized early motor, sensory, and autonomic outcomes of 2 volumes of compression (10 and 15 microl) using behavioral tests and then examined histological outcomes in the spinal cord using Luxol fast blue staining. To further substantiate the characterization of the epidural balloon-compression model, they used a noncompetitive N-methyl-D-aspartate antagonist, GK11, and demonstrated the involvement of excitotoxicity in this model. RESULTS: Proportional and reproducible functional impairment resulted from compression caused by balloon inflation with either 10 or 15 microl of water and corresponded to the extent of the lesion. Indeed, during the early phase following SCI (1 week postinjury), recovery of locomotor function and bladder control correlated with the volume of inflation, whereas outcomes with respect to sensory function and reflexes were independent of compression severity. Treatment with GK11 significantly improved motor function in all groups of rats 1 week after injury and bladder voiding in the 10-microl injured rats compared to the 15-microl injured rats. CONCLUSIONS: The results of this study demonstrate that spinal balloon-compression injury in the rat is a well-characterized, reproducible, and predictable model to analyze early events following SCI.

A remotely controlled model of spinal cord compression injury in mice: toward real-time analysis.

OBJECT: To date, there has been no efficient therapeutic approach to spinal cord injuries (SCIs). This may be attributable, at least in part, to difficulties in forming predictive and accurate experimental animal models. The authors' previous studies have identified 2 relevant conditions of such a model. The first condition is the ability to compare data derived from rat models of SCI by developing mouse models of SCI that permit access to a large range of transgenic models. The second condition is that the exploration of the consequences of each mechanism of spinal trauma requires modeling the different etiologic aspects of the injury. METHODS: To fulfill these 2 conditions a new model of mouse spinal cord compression injury was devised using a thread-driven olive-shaped compressive device. The authors characterized early motor, sensory, and histological outcomes using 3 olive diameters and different compression durations. RESULTS: A gradual and reproducible functional severity that correlated with lesion extension was demonstrated in 76 mice. To further substantiate the characterization of this model, a noncompetitive N-methyl-d-aspartate antagonist was administered in 30 mice, which demonstrated the involvement of excitotoxicity in this model. CONCLUSIONS: The study demonstrated that spinal olive-compression injury in the mouse is a reproducible, well-characterized, and predictable model for analyzing early events after SCI. The nonmagnetic and remotely controlled design of this model will allow completion of the lesion while the animal is in the MR imaging apparatus, thus permitting further real-time MR imaging studies that will provide insights into the characterization of early events in the spatial and temporal evolution of SCI. Moreover, this model lays the foundation for future in vivo studies of functional and histological outcomes following SCI in genetically engineered animals.

Minimum information about animal experiments: supplier is also important.

It has now been established that functional recovery after spinal cord injury (SCI) depends on several parameters, including animal strain. Here we demonstrate that rats from the same strain (Wistar) but from two independent commercial suppliers present different motor, sensory, and autonomic outcomes after a standard model of SCI, the so-called compression model. Recovery is correlated with the extension of the lesion, and we show that the vertebral canal diameter varies between the two suppliers. To substantiate this point, we carried out another set of experiments, with the so-called contusion model, which requires bone ablation and thus whose extension is not related to vertebral canal diameter. We show that there is no difference between the two suppliers. The purpose of our communication is to alert researchers on how crucial it is to control experimental parameters as closely as possible and to establish a standard for animal experiment in order to avoid unexpected biases.

Time course of acute phase in mouse spinal cord injury monitored by ex vivo quantitative MRI.

During the acute phase of spinal cord injury (SCI), major alterations of white and grey matter are a key issue, which determine the neurological outcome. The present study with ex vivo quantitative high-field magnetic resonance microimaging (MRI) was intended in order to identify sensitive parameters of tissue disruption in a well-controlled mouse model of ischemic SCI. MR imaging evidenced changes as early as the second hour after the lesion in the dorsal horns, which appear swollen. After 4 h, alterations of the white matter of dorsal and lateral funiculi were reflected by a progressive loss of white/grey matter contrast with further ventral extension by the 24th hour. Diffusion tensor imaging and multi-exponential T2 measurements permitted to quantify these physicochemical, time-related, alterations during the 24-h period. This characterization of spatial and temporal evolution of SCI will contribute to better define both the most appropriate targets for future therapies and more accurate therapeutic windows. Upcoming directions include the use of these parameters on in vivo animal models and their application to clinics. Indeed, magnetic resonance techniques appear now as a major non-invasive translation tool in CNS pathologies based on the development of more appropriate pre-clinical models.

A mouse model of acute ischemic spinal cord injury.

Mice models of spinal cord injury (SCI) should improve our knowledge of the mechanisms of injury and repair of the nervous tissue. They represent a powerful tool for the development of therapeutic strategies in the fields of pharmacological, cellular, and genetic approaches of neurotrauma. We demonstrate here that the photochemical graded ischemic spinal cord injury model, described in rats, can be successfully adapted in mice, in a reliable and reproducible manner. Following the intravenous injection of Rose Bengal, the translucent dorsal surface of the T9 vertebral laminae of C57BL/6 female mice was irradiated with a 560-nm wavelength-light (3-8 min depending on the experimental group). Animals were sacrificed at 1 day or 7 days after injury. Functional tests were performed daily for motor, sensory, autonomic, and reflex responses. Lesion histopathology was assessed for lesion length, percentage of residual white matter, and astrocytic reactivity. Experimental groups demonstrated a functional deficit, which was correlated to the increase of the irradiation time and, therefore, to the severity of the injury. Histopathological and immunocytochemical data were reliable morphological measurements characterizing the degree of injury, which were strongly correlated to the severity of the functional impairment. Despite differences in the mechanism of injury, the wound healing response described in other traumatic SCI mice models was confirmed (no cavitation and, conversely, the formation of a dense connective tissue matrix). In this context, the precise understanding of the mechanisms of healing response after SCI in mice and of neurochemical kinetics appear to be crucial in the development of therapeutic strategies of CNS repair. Thus, the possible use of an increasing collection of transgenic mice offers a new dimension for experimental research in this area. The ischemic photochemical model of SCI in mice represents a relevant model that can play a key role in this new era of neurotrauma research.