Noelle Callizot

Interleukin-6 attenuates the development of experimental diabetes-related neuropathy.

Neuropathy is the most severe and the least understood complication of diabetes. We investigated the potential neuroprotective effect of IL‐6 therapy in an experimental model of diabetic neuropathy. A single i.v. injection of streptozotocin (STZ, 55 mg/kg) was used to induce experimental diabetes in adult males. IL‐6 (1, 10 or 30 µg/kg) was administrated either intraperitoneally on a daily basis or subcutaneously (s.c.) on a daily, on a three times or one time per week basis, starting at day 10 post‐STZ. A decrease in sensory nerve conduction velocity (SNCV), indicative of neuropathy, is seen in STZ rats as early as day 10 post‐STZ, a time at which blood glycaemia is already maximal. At later time points, this electrophysiological impairment became severe and clinically apparent by affecting tail flick latency. Motor dysfunction defined by a significant increase in compound muscle action potential (CMAP) latency was also recorded. At the completion of the study (day 40 post‐STZ), histological examination revealed significant axonopathy and myelin loss, along with an increase in the proportion of fibers with abnormal appearance in sciatic nerves of STZ rats. These changes were not observed in non‐diabetic rats and were significantly prevented by IL‐6 treatment. The optimal dose appeared to be 10 µg/kg s.c. three injections per week, which showed a better effect in most of the parameters studied than 4‐methylcatechol, a NGF‐like neuroprotective compound. Once weekly and three times weekly administrations of IL‐6 were as effective as daily treatment. Taken together, these results support the potential neuroprotective actions of IL‐6. The fact that the half‐life of IL‐6 is only approximately 5 h while weekly dosing was neuroprotective strongly suggests activation by IL‐6 of effector molecule(s) with longer duration of action.

Pyridoxine-Induced Neuropathy in Rats: A Sensory Neuropathy That Responds to 4-Methylcatechol

Sensory neuropathies are frequently associated with diabetes or with antimitotic treatments in humans suffering from cancer, and are in this case the most important limitation to the use of antimitotic drugs. For this reason, there is a need to establish and validate animal models of sensory neuropathies that could be routinely used, together with the already known models, for studying and evaluating the effects of putative neuroprotective compounds. In the present study, we prove by behavioral and electromyographical analyses that (a) it is possible to induce a nonlethal, exclusively sensory, reversible neuropathy by intoxicating rats with large amounts of pyridoxine, using a new schedule of intoxication; (b) 4-methylcatechol, a drug known to induce nerve growth factor synthesis, improves the clinical status of pyridoxine-intoxicated animals, shortens the duration of the disease, and restores the morphological integrity of the sensory fibers. Owing to its mode of installation and its clinical features, we propose that this model be used as an additional model for preclinical studies of neuroprotective drugs.

A new long term in vitro model of myelination

Besides in vivo models, co-cultures systems making use of Rat dorsal root ganglion explants/Schwann cells (SC) are widely used to essentially study myelination in vitro. In the case of animal models of demyelinating diseases, it is expected to reproduce a pathological process; conversely the co-cultures are primarily developed to study the myelination process and in the aim to use them to replace animals in experiences of myelin destruction or functional disturbances. We describe (in terms of protein expression kinetic) a new in vitro model of sensory neurons/SC co-cultures presenting the following advantages: both sensory neurons and SC originate from the same individual; sensory neurons and SC being dissociated, they can be co-cultured in monolayer, allowing an easier microscope observation; the co-culture can be maintained in a serum-free medium for at less three months, allowing kinetic studies of myelin formation both at a molecular and cellular level. Optimizing culture conditions permits to use 96-well culture plates; image analyses conducted with an automatic image analyzer allows rapid, accurate and quantitative expression of results. Finally, this system was proved by measuring the apparition of myelin protein to mimic in vitro the physiological process of in vivo myelination.

Combining two repurposed drugs as a promising approach for Alzheimer's disease therapy

Alzheimer disease (AD) represents a major medical problem where mono-therapeutic interventions demonstrated only a limited efficacy so far. We explored the possibility of developing a combinational therapy that might prevent the degradation of neuronal and endothelial structures in this disease. We argued that the distorted balance between excitatory (glutamate) and inhibitory (GABA/glycine) systems constitutes a therapeutic target for such intervention. We found that a combination of two approved drugs – acamprosate and baclofen – synergistically protected neurons and endothelial structures in vitro against amyloid-beta (Aβ) oligomers. The neuroprotective effects of these drugs were mediated by modulation of targets in GABA/glycinergic and glutamatergic pathways. In vivo, the combination alleviated cognitive deficits in the acute Aβ25–35 peptide injection model and in the mouse mutant APP transgenic model. Several patterns altered in AD were also synergistically normalised. Our results open up the possibility for a promising therapeutic approach for AD by combining repurposed drugs.

The frissonnant mutant mouse, a model of dopamino-sensitive, inherited motor syndrome.

The frissonnant (fri) mutation is an autosomic recessive mutation which spontaneously appeared in the stock of C3H mice. fri mutant mice have locomotor instability and rapid tremor. Since tremor ceases when mutant mice have sleep or are anaesthetized, and because of their obvious stereotyped motor behavior, these mice could represent an inherited Parkinsonian syndrome. We show here that the fri/fri mouse fulfills two out of the three criteria required to validate an experimental model of human disease, that is isomorphism, homology and predictivity. Indeed, fri/fri mice present an important motor deficit accompanying visible tremor and stereotypies. They display some memory deficits as in human Parkinsons desease. l-Dopa and apomorphine (dopaminergic agonists), ropinirole (selective D2 agonist), and selegiline (an monoamino-oxidase B [MAO-B] inhibitor) improve their clinical status. However, neither anatomopathological evidence of nigrostriatal lesion, nor decrease in tyrosine hydroxylase production could be seen.

Operational dissection of β-amyloid cytopathic effects on cultured neurons.

Alzheimer disease (AD) affects mainly people over the age of 65 years, suffering from different clinical symptoms such as progressive decline in memory, thinking, language, and learning capacity. The toxic role of β‐amyloid peptide (Aβ) has now shifted from insoluble Aβ fibrils to smaller, soluble oligomeric Aβ aggregates. The urgent need for efficient new therapies is high; robust models dissecting the physiopathological aspects of the disease are needed. We present here a model allowing study of four cytopathic effects of Aβ oligomers (AβO): oxidative stress, loss of synapses, disorganization of the neurite network, and cellular death. By generating a solution of AβO and playing on the concentration of and time of exposure to AβO, we have shown that it was possible to reproduce early effects (oxidative stress) and the long‐term development of structural alterations (death of neurons). We have shown that 1) all toxic events were linked to AβO according to a specific timing and pathway and 2) AβO were probably the key intermediates in AD pathogenesis. The present model, using Aβ peptide solution containing AβO, reproduced essential neuropathological features of AD; the effects involved were similar whatever the kind of neurons tested (cortical vs. hippocampal). By using a single system, it was possible to embrace all toxic mechanisms at defined times and concentrations, to study each involved pathway, and to study the effects of new molecules on the different neurotoxic pathways responsible for development of AD.

Glutamate protects neuromuscular junctions from deleterious effects of β-amyloid peptide and conversely: an in vitro study in a nerve-muscle coculture.

Murine models of Alzheimers disease with elevated levels of amyloid‐β (Aβ) peptide present motor axon defects and neuronal death. Aβ1–42 accumulation is observed in motor neurons and spinal cords of sporadic and familial cases of amyotrophic lateral sclerosis (ALS). Motor neurons are highly susceptible to glutamate, which has a role in ALS neuronal degeneration. The current study investigates the link between Aβ and glutamate in this neurodegenerative process. Primary rat nerve and human muscle cocultures were intoxicated with glutamate or Aβ. Neuromuscular junction (NMJ) mean size and neurite length were evaluated. The role of N‐methyl‐D‐aspartate receptor (NMDAR) was investigated by using MK801. Glutamate and Aβ production were evaluated in culture supernatant. The current study shows that NMJs are highly sensitive to Aβ peptide, that the toxic pathway involves glutamate and NMDAR, and that glutamate and Aβ act in an interlinked manner. Some motor diseases (e.g., ALS), therefore, could be considered from a new point of view related to these balance disturbances.

Theoretical Considerations on Animal Models

Aimed at studying human diseases, animal models emerged in the 1800s and underwent a real boom during the last century. Whether isomorphic or homologous - a categorization based on the extent of similarities between human and animal diseases -, animal models have led to tremendous progress in therapeutics. Following an introduction about history and ethical issues of animal models, this article describes their main features. What are the different kinds of animal models? What characterizes induced (experimental) disease, spontaneous disease, transgenic disease, negative disease and orphan disease models? What are the limits and pitfalls of animal models? What parameters should be taken into consideration for a better predictivity of the models? Various examples taken in the discipline of neuroscience, and even psychiatry, illustrate the difficulties, success and concerns of animal modelling.

Pyridoxine-Induced Peripheral Neuropathy

The neurotoxicity induced by an excess of vitamin B6 in animals has been known for many years but the first human clinical cases have only recently been reported. All subjects showed paraesthesia an

A Dopamine-Sensitive Inherited Motor Syndrome Linked to the frissonnant Mutation

The frissonnant (fri) mutation is an autosomal recessive mutation which spontaneously appeared in 1977 in the stock of C3H mice of the Pasteur Institute in Paris. fri/fri mutation causes locomotor i