Taiep Rats Research Articles

4-aminopyridine improves evoked potentials and ambulation in the taiep rat: A model of hypomyelination with atrophy of basal ganglia and cerebellum.

The taiep rat is a tubulin mutant with an early hypomyelination followed by progressive demyelination of the central nervous system due to a point mutation in the Tubb4a gene. It shows clinical, radiological, and pathological signs like those of the human leukodystrophy hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC). Taiep rats had tremor, ataxia, immobility episodes, epilepsy, and paralysis; the acronym of these signs given the name to this autosomal recessive trait. The aim of this study was to analyze the characteristics of somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) in adult taiep rats and in a patient suffering from H-ABC. Additionally, we evaluated the effects of 4-aminopyridine (4-AP) on sensory responses and locomotion and finally, we compared myelin loss in the spinal cord of adult taiep and wild type (WT) rats using immunostaining. Our results showed delayed SSEPs in the upper and the absence of them in the lower extremities in a human patient. In taiep rats SSEPs had a delayed second negative evoked responses and were more susceptible to delayed responses with iterative stimulation with respect to WT. MEPs were produced by bipolar stimulation of the primary motor cortex generating a direct wave in WT rats followed by several indirect waves, but taiep rats had fused MEPs. Importantly, taiep SSEPs improved after systemic administration of 4-AP, a potassium channel blocker, and this drug induced an increase in the horizontal displacement measured in a novelty-induced locomotor test. In taiep subjects have a significant decrease in the immunostaining of myelin in the anterior and ventral funiculi of the lumbar spinal cord with respect to WT rats. In conclusion, evoked potentials are useful to evaluate myelin alterations in a leukodystrophy, which improved after systemic administration of 4-AP. Our results have a translational value because our findings have implications in future medical trials for H-ABC patients or with other leukodystrophies.

Characterization of sperm motility and testosterone secretion in the taiep myelin mutant, a model of demyelination.

Presently, demyelinating diseases have been reported to affect the reproductive life of patients who suffer from them, but the progression of the alterations is unknown, especially in men. To better understand these effects, it is necessary to perform studies in animal models, such as the male taiep rat, which exhibits progressive demyelination of the central nervous system, altered kisspeptin expression at the hypothalamic level, and decreased luteinizing hormone, which could alter sperm quality and testicular diameter. Thus, the objective of the present study was to analyze the diameter of the seminiferous tubules, the sperm motility, and the testosterone levels of 90-day-old male taiep rats. The obtained results indicate that male taiep rats show an increase in testicular size accompanied by an increase in the diameter of the seminiferous tubules of the left testicle. There was also a decrease in progressive motility in sperm samples from the left epididymis of male taiep rats compared to the control group, with no changes in serum testosterone concentration. Therefore, we conclude that male taiep rats with central demyelination show altered testicular diameter and decreased motility in sperm from the left side. This type of studies serves as a basis for proposing possible reproductive strategies to improve the fertility and testicular function of men with demyelinating diseases of the central nervous system.

H-ABC tubulinopathy revealed by label-free second harmonic generation microscopy

Hypomyelination with atrophy of the basal ganglia and cerebellum is a recently described tubulinopathy caused by a mutation in the tubulin beta 4a isoform, expressed in oligodendrocytes. The taiep rat is the only spontaneous tubulin beta 4a mutant available for the study of this pathology. We aimed to identify the effects of the tubulin mutation on freshly collected, unstained samples of the central white matter of taiep rats using second harmonic generation microscopy. Cytoskeletal differences between the central white matter of taiep rats and control animals were found. Nonlinear emissions from the processes and somata of oligodendrocytes in tubulin beta 4a mutant rats were consistently detected, in the shape of elongated structures and cell-like bodies, which were never detected in the controls. This signal represents the second harmonic trademark of the disease. The tissue was also fluorescently labeled and analyzed to corroborate the origin of the nonlinear signal. Besides enabling the description of structural and molecular aspects of H-ABC, our data open the door to the diagnostic use of nonlinear optics in the study of neurodegenerative diseases, with the additional advantage of a label-free approach that preserves tissue morphology and vitality.

Sex-specific hypothalamic expression of kisspeptin, gonadotropin releasing hormone, and kisspeptin receptor in progressive demyelination model

Demyelinating diseases, such as multiple sclerosis, decrease the quality of life of patients and can affect reproduction. Assisted reproductive therapies are available, which although effective, aggravate motor symptoms. For this reason, it is important to determine how the control of the hypothalamus-pituitary-gonadal axis is affected in order to develop better strategies for these patients. One way to determine this is using animal models such as the taiep rat, which shows progressive demyelination of the central nervous system, and was used in the present study to characterize the expression of gonadotrophin-releasing hormone (GnRH), Kisspeptin, and kisspeptin receptor (Kiss1R) and luteinizing hormone (LH) secretion. The expression of kisspeptin, GnRH, and Kiss1R was determined at the hypothalamic level by immunofluorescence and serum LH levels were determined by ELISA. The expression of kisspeptin at the hypothalamic level showed sexual dimorphism, where there was an increase in males and a decrease in females during oestrus. There was no change in the expression of GnRH or kisspeptin receptor, regardless of sex. However, a decrease in serum LH concentration was observed in both sexes. The taiep rat showed changes in the expression of kisspeptin at the hypothalamic level. These changes are different from those reported in the literature with the use of animals with experimental allergic encephalomyelitis, this is because both animal models represent different degrees of progression of multiple sclerosis. Our results suggest that the effects on the hypothalamus-pituitary-gonadal axis depend on the differences between the demyelinating processes, their progression, and even individual factors, and it is thus important that fertility treatments are individualized to maximize therapeutic effects.

0280 Orexins play a dual role in immobility episodes on taiep rats a model of H-ABC

Abstract Introduction Leukodystrophies are a heterogenous group of congenital myelin alterations with more than 30 classified diseases was described until now. Among them there are several mutations in the a and b tubulins the so called tubulinophaties, that affect the central nervous system. The hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) is due to a mutation in the tubulin b 4a (TUBB4A) and the taiep rats is the only available model of this human disease with similar magnetic resonance changes and a punctual mutation in the TUBB4A. Taiep rats had immobility episodes (IEs) with a peak between at 9 months of age. Importantly, electroencephalographic recordings shown that IEs had a rapid eye movement (REM) sleep characteristic pattern supporting that are equal to human cataplexy episodes that are key sign of narcolepsy. It is possible to induced IEs when taiep rats are manipulated from the tail or the thorax. Narcolepsy in humans and narcoleptic dogs had a significant decreased in orexin levels in the cerebrospinal fluid (CSF) and a concomitantly decreased of orexin neurons in the lateral hypothalamus. Methods We used 21 male rats from taiep at 9 months of age. All rats were kept in standard conditions and were implanted for EEG, EMG and EOG recordings to characterize IEs. We administered orexin A and B agonists and characterized the sleep-wake cycle and frequency of IEs, the peptides were administered by a intracerebroventricular (i.c.v.) injections diluted in artificial CSF. We also measured the number or positive orexin neurons in the lateral hypothalamus through immunohistochemistry. Results The i.c.v. administration of [Ala11, D-Leu 15] orexin B agonist significantly decrease the frequency of IEs with 3 and 10 nM doses (P≤0.05 and P≤0.03, respectively), without affecting the sleep-wake pattern. However, the i.c.v. administration of Orexin A (17-33) an agonist did not affect the sleep-wake pattern or the frequency of IEs. It is relevant that the number of orexins neurons did not differ between taiep and control Sprague-Dawley (SD) male rats. Conclusion Our results showed that IEs had a REM sleep EEG characteristic pattern with cataplexic-like atonia, there are sensible to orexin B agonist, but the number of orexin positive neurons do not differ with respect to SD male rats. In conclusion taiep rats a model of H-ABC is an adequate model of cataplexy-like episodes due to myelin disease. Support (If Any) Partially supported by PRONACES-CONACYT grant 194171, and VIEP-BUAP 2021 to CA in Neuroendocrinología. KGE is fellowship from CONACYT No. 772626.

0134 Circadian variation of absence seizures in an animal model of human leukodystrophy (H-ABC)

Abstract Introduction Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) is a human leukodystrophy is due to a mutation in the tubulin b 4a (TUBB4A) and the taiep rats is the only available model of this human disease with similar signs in the magnetic resonance imaging and a mutation in the TUBB4 that induced an accumulation of microtubules in the cytoplasm and its processes in the oligodendrocytes. Taiep rats had spike-wave discharges (SWD) that are similar to absence epilepsy with a progressive increase with the age of the subjects. The aim of this study is to analyze the circadian distribution of SWD on male taiep. Methods We used 16 male taiep rats at 6 and 9 months of age. All rats were kept in standard conditions with a 12/12 light-dark cycle (lights on at 0700) and free access to rodent food pellets and purified water and were implanted for EEG, EMG and EOG recordings to characterize the frequency and duration of SWD. All procedures followed the NIH rules, and the protocol was approved by BUAP-IACUC. Results The number of SWD are higher in male rats at 9 with respect to 6 months of age (P≤0.05), and also had higher incidence during the light phase with respect to the dark phase (P≤0.05). The duration of SWD had also a greater duration during the light period than the dark phase (P≤0.05). Conclusion Our results showed that SWD has higher incidence of SWD and of longer duration during the light period when the rats had more sleep suggesting that the neurotransmitters that are released during sleep facilitate the discharge in the thalamo-cortical circuit that support SWD. Support (If Any) Partially supported by PRONACES-CONACYT grant 194171, and VIEP-BUAP 2021 to CA in Neuroendocrinología. JMI is fellowship from CONACYT No. 735813.

Testicular androgens determining the incidence of spike-wave discharges in taiep rats: A model of H-ABC leukodystrophy

Absence seizures are characterized as a generalized type of epilepsy that occurs during childhood. Importantly, absence seizures in children often discontinue after puberty. There is limited availability of animal models in which electroencephalography (EEG) can be performed in the long term; however, two absence seizure models, GAERS and WAG/Rij albino rats, are available. The taiep rat is a myelin mutant rat with tubulinopathy due to a tubulin β 4A gene mutation and characteristic spike-wave discharges (SWDs) that mimic absence seizure epilepsy in humans and the above rat models. This study aimed to analyze spike-wave discharges after an orchiectomy was performed on postnatal day (PND) 2 or PND 90 in adult rats; and SWDs was recorded in both groups on PND 104. The results suggest that androgens play a critical role in susceptibility to SWDs. In fact, orchiectomy during the neonatal period significantly reduced the frequency of spike-wave discharges. However, if an orchiectomy was performed in adulthood, then SWDs were significantly increased. The mean duration of spike-wave discharges did not differ among the groups tested. Acute administration of testosterone (1 mg/kg) did not change the frequency or duration of spike-wave discharges in the control group or both orchiectomized groups. Overall, this study is the first to show a dichotomic influence of testicular androgens on spike-wave discharges. These findings will have implications in children with this type of generalized epilepsy and may explain the disappearance of absence epilepsy in two-thirds of patients after puberty.

Characterization of the Kisspeptin and GnRH expression in the hypothalamus of the male and female taiep rat, an animal model of demyelination.

Reproductive alterations have been reported in patients with demyelinating diseases, these alterations can lead to infertility. In the hypothalamus we can find two neuronal types that regulate reproductive function; kisspeptidergic and GnHergic neurons. At the present moment, the relation between demyelination and reproductive alterations it is yet unknown; in order to elucidate this relation, we used the taiep rat, an animal that presents demyelination of the central nervous system and that also shows reproductive issues. We characterized the immunofluorescent expression of kisspeptin and GnRH in the hypothalamus of the male and female taiep rats using Sprague-Dawley rats as control. We obtained the brains of the females during oestrous and adult males; the brains were cut at 10mm. Performed immunofluorescence of kisspeptin and GnRH (bs-0749r-cy5, bs-10369R-A488; Bioss Antibodies) and analysed the intensity of the fluorescence in the hypothalamus using the software ImageJ1.50i. Fluorescence is concentrated in fiber-like structures with neuron shape. An increment in the intensity of the fluorescence of kisspeptin was observed in said structures in male taiep rats compared with SD (0.37±0.02 vs 0.28±0.01, p< 0.001). Female taiep rats during oestrus showed a decrease in the intensity of the fluorescence of kisspeptin structures compared with SD (0.44±0.02 vs 0.57±0.03, p< 0.001). We could not observe any significant changes in the expression of GnRH fibers in the hypothalamus of the taiep rat compared with SD. Demyelination in the taiep rat affects kisspeptin expression at hypothalamic level, but this does not affect the expression of GnRH in either males or females, this effect is probably related with the availability of receptors in the GnRHergic neuron, we will evaluate this in the future. The decrease in kisspeptin expression in the female taiep rat, could be caused by previously reported low concentrations of oestrogen, given that it is capable of stimulating kisspeptin expression.

Longitudinal Evaluation of Cerebellar Signs of H-ABC Tubulinopathy in a Patient and in the taiep Model.

Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) is a central neurodegenerative disease due to mutations in the tubulin beta-4A (TUBB4A) gene, characterized by motor development delay, abnormal movements, ataxia, spasticity, dysarthria, and cognitive deficits. Diagnosis is made by integrating clinical data and radiological signs. Differences in MRIs have been reported in patients that carry the same mutation; however, a quantitative study has not been performed so far. Our study aimed to provide a longitudinal analysis of the changes in the cerebellum (Cb), corpus callosum (CC), ventricular system, and striatum in a patient suffering from H-ABC and in the taiep rat. We correlated the MRI signs of the patient with the results of immunofluorescence, gait analysis, segmentation of cerebellum, CC, and ventricular system, performed in the taiep rat. We found that cerebellar and callosal changes, suggesting a potential hypomyelination, worsened with age, in concomitance with the emergence of ataxic gait. We also observed a progressive lateral ventriculomegaly in both patient and taiep, possibly secondary to the atrophy of the white matter. These white matter changes are progressive and can be involved in the clinical deterioration. Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) gives rise to a spectrum of clinical signs whose pathophysiology still needs to be understood.

Long-term taurine administration improves motor skills in a tubulinopathy rat model by decreasing oxidative stress and promoting myelination

The taiep rat undergoes hypomyelination and progressive demyelination caused by an abnormal microtubule accumulation in oligodendrocytes, which elicits neuroinflammation and motor behavior dysfunction. Based on taurine antioxidant and proliferative actions, this work explored whether its sustained administration from the embryonic age to adulthood could prevent neuroinflammation, stimulate cell proliferation, promote myelination, and relieve motor impairment. Taurine (50 mg/L of drinking water = 50 ppm) was given to taiep pregnant rats on gestational day 15 and afterward to the male offspring until eight months of age. We measured the levels of nitric oxide (NO), malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA), CXCL1, CXCR2 receptor, growth factors (BNDF and FGF2), cell proliferation, and myelin content over time. Integral motor behavior was also evaluated. Our results showed that taurine administration significantly decreased NO and MDA + 4-HDA levels, increased cell proliferation, and promoted myelination in an age- and brain region-dependent fashion compared with untreated taiep rats. Taurine effect on chemokines and growth factors was also variable. Taurine improved vestibular reflexes and limb muscular strength in perinatal rats and fine movements and immobility episodes in adult rats. These results show that chronic taurine administration partially alleviates the taiep neuropathology.

The deficiency of myelin in the mutant taiep rat induces a differential immune response related to protection from the human parasite Trichinella spiralis.

Taiep rat is a myelin mutant with a progressive motor syndrome characterized by tremor, ataxia, immobility episodes, epilepsy and paralysis of the hindlimbs. Taiep had an initial hypomyelination followed by a progressive demyelination associated with an increased expression of some interleukins and their receptors. The pathology correlated with an increase in nitric oxide activity and lipoperoxidation. In base of the above evidences taiep rat is an appropriate model to study neuroimmune interactions. The aim of this study was to analyze the immune responses in male taiep rats after acute infection with Trichinella spiralis. Our results show that there is an important decrease in the number of intestinal larvae in the taiep rat with respect to Sprague-Dawley control rats. We also found differences in the percentage of innate and adaptive immune cell profile in the mesenteric lymphatic nodes and the spleen that correlated with the demyelination process that took place on taiep subjects. Finally, a clear pro-inflammatory cytokine pattern was seen on infected taiep rats, that could be responsible of the decrement in the number of larvae number. These results sustain the theory that neuroimmune interaction is a fundamental process capable of modulating the immune response, particularly against the parasite Trichinella spiralis in an animal model of progressive demyelination due to tubulinopathy, that could be an important mechanism for the clinical course of autoimmune diseases associated with parasite infection.

MRI Features in a Rat Model of H-ABC Tubulinopathy.

Tubulinopathies are a group of recently described diseases characterized by mutations in the tubulin genes. Mutations in TUBB4A produce diseases such as dystonia type 4 (DYT4) and hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC), which are clinically diagnosed by magnetic resonance imaging (MRI). We propose the taiep rat as the first animal model for tubulinopathies. The spontaneous mutant suffers from a syndrome related to a central leukodystrophy and characterized by tremor, ataxia, immobility, epilepsy, and paralysis. The pathological signs presented by these rats and the morphological changes we found by our longitudinal MRI study are similar to those of patients with mutations in TUBB4A. The diffuse atrophy we found in brain, cerebellum and spinal cord is related to the changes detectable in many human tubulinopathies and in particular in H-ABC patients, where myelin degeneration at the level of putamen and cerebellum is a clinical trademark of the disease. We performed Tubb4a exon analysis to corroborate the genetic defect and formulated hypotheses about the effect of amino acid 302 change on protein physiology. Optical microscopy of taiep rat cerebella and spinal cord confirmed the optical density loss in white matter associated with myelin loss, despite the persistence of neural fibers.

0428 Taiep Rats Had Normal Levels of Orexin Neurons in the Lateral Hypothalamus But Their Cataplexy Attacks are Sensible to Specific Orexin B Agonist

Abstract Introduction Narcolepsy is characterized by sleep fragmentation, sleep paralysis, hypnagogic hallucinations and cataplexy. The cataplexy is a sudden loss of muscle tone triggered by emotions in humans, as well as in animal models. It is stablished that most of the patients had a significant decrease of orexin neurons in the lateral hypothalamus. Taiep rats had a mutation in tubulin TUBB4A and suffer immobility episodes (IE′s) that had a desynchronized activity in the cortex associated with theta rhythm in the hippocampus similar to narcolepsy patients. The aim of this study was to analyze the effects of central administration of an orexin B agonist and determination by immunohistochemistry of the number of orexin neurons on adult male taiep rats. Methods We used 14 male taiep rats of 9 months of age. The subjects (Ss) lived 3-4 in acrylic cages with water and food pellets ad libitum, under a 12:12 light-dark cycle (lights on at 0700), whit-controlled temperature and humidity in the recording room. All Ss were implanted to record EEG, EMG and EOG to characterize immobility episodes (IE′s) in a control 8 h recording and after i.c.v. administration of [Ala 11, D-Leu 15]-orexin B with 1, 3 and 10 nmol/1 μL. We measured the number, mean duration and latency to the first IE′s. Results The administration of [Ala 11, D-Leu 15]-orexin B significantly reduced the number of IE′s (P&amp;lt;0.01), from 4.28 ± 1.5 IE′s to just 0.25 ± 0.17 with 10 nmol/1 μL dose, but did not change the amount of awakening, slow wave or rapid eye movement sleep. Importantly, the number or orexins neurons were similar between taiep and Sprague-Dawley rats. Conclusion The myelin mutant taiep rats is a model of narcolepsy with cataplexy with normal number of orexin neurons in the lateral hypothalamus. Additionally, a specific orexin B agonist reduced IE′s without any effect the sleep pattern. This could be useful for the design of new treatments. Support CONACYT grants 243333 and 243247 to CC and JRE, respectively. Grants from VIEP-BUAP 2019 and CA in Neuroendocrinología BUAP-CA-288.

0427 Bicuculine Increased the Cataplexy in the Male Taiep Rats: An Animal Model of Narcolepsy with an Inherent Tubulopathy

Abstract Introduction Narcolepsy is a hypersomnolence that is characterized by sleep fragmentation, sleep paralysis, hypnagogic hallucinations and cataplexy that is characterized by atonia induced by strong emotions. The amygdala is the trigger for cataplexy through GABAergic mechanisms. Taiep is a myelin mutant with TUBB4A tubulopathy which showed spontaneous episodes of atonia or induced by manipulations from the tail or the thorax. EEG recordings during immobility episodes (IE′s) had a cerebral cortex desynchronized associated to theta rhythm in the hippocampus. The aim of this sturdy was to analyze the effects of bicuculine administration on IE′s and sleep-wake pattern on adult male taiep rats. Methods We used 6 taiep male rats at 9 months of age. The subjects (Ss) lived in individual acrylic cages with water and food pellets available ad libitum, under a 12:12 light-dark cycle (lights on at 0700), with controlled temperature and humidity recording room. All Ss were implanted to record EEG, EMG and EOG to characterize EI′s. We evaluated a basal 24 h EEG recording and then after bicuculine i.p. administration of 0.5, 1 y 1.5 mg/Kg every 48h. We measured the number, mean duration and latency to the first IE′s. Results The duration of IE′s increased 527% with 1 mg/Kg and reach 700% with 1.5 mg/Kg of bicuculine (P&amp;lt;0.01) with respect to saline-treated control group. Importantly, the frequency of IEs did not differ among the groups and did not affect the number of awake, slow wave or rapid eye movements sleep phases. Conclusion Bicuculine, a specific GABA antagonist, modify the duration of IES but not their frequency supporting a role of GABAergic mechanism on IE′s. It is relevant because sodium oxybate, an indirect GABA agonist, reduced cataplexy and improved sleep quality on narcoleptic patients. Support CONACYT grants 243333 and 243247 to CC and JRE, respectively and from VIEP-BUAP 2019 to CA in Neuroendocrinología BUAP-CA-288.

Juvenile Taiep rats have shorter dendritic trees in the dorsal field of the hippocampus without spatial learning disabilities.

Myelin mutant taiep rats show a progressive demyelination in the central nervous system due to an abnormal accumulation of microtubules in the cytoplasm and the processes on their oligodendrocytes. Demyelination is associated with electrophysiological alterations and the mutant had a progressive astrocytosis. The illness is associated with change in cytokine levels and in the expression of different nitric oxide synthase and concomitantly lipoperoxidation in several areas of the brain. However, until now there has been no detailed anatomical analysis of neurons in this mutant. The aim of this study was to analyze the dendritic morphology in the hippocampus using Golgi-Cox staining and spatial memory through Morris water maze test in young adult (3 months old) taiep rats and compare them with normal Sprague-Dawley. Our results showed that taiep rats have altered dendritic tree morphology in pyramidal neurons in the CA1 field of the hippocampus, but not in the CA3 region. These morphological changes did not produce a concomitant deficit in spatial memory acquisition or recall at this early stage of the disease. Our results suggest that impairment of dendritic morphology in the CA1 field of the hippocampus is a landmark of the pathology of this progressive multiple sclerosis model.

A mutation in the Tubb4a gene leads to microtubule accumulation with hypomyelination and demyelination

Our goal was to define the genetic cause of the profound hypomyelination in the taiep rat model and determine its relevance to human white matter disease. Based on previous localization of the taiep mutation to rat chromosome 9, we tested whether the mutation resided within the Tubb4a (β-tubulin 4A) gene, because mutations in the TUBB4A gene have been described in patients with central nervous system hypomyelination. To determine whether accumulation of microtubules led to progressive demyelination, we analyzed the spinal cord and optic nerves of 2-year-old rats by light and electron microscopy. Cerebral white matter from a patient with TUBB4A Asn414Lys mutation and magnetic resonance imaging evidence of severe hypomyelination were studied similarly. As the taiep rat ages, there is progressive loss of myelin in the brain and dorsal column of the spinal cord associated with increased oligodendrocyte numbers with accumulation of microtubules. This accumulation involved the entire cell body and distal processes of oligodendrocytes, but there was no accumulation of microtubules in axons. A single point mutation in Tubb4a (p.Ala302Thr) was found in homozygous taiep samples. A similar hypomyelination associated with increased oligodendrocyte numbers and arrays of microtubules in oligodendrocytes was demonstrated in the human patient sample. The taiep rat is the first animal model of TUBB4 mutations in humans and a novel system in which to test the mechanism of microtubule accumulation. The finding of microtubule accumulation in a patient with a TUBB4A mutation and leukodystrophy confirms the usefulness of taiep as a model of the human disease. Ann Neurol 2017;81:690-702.

The Myelin Mutant Rat Taiep as a Model of Neuroimmunological Disease

Taiep rat is a myelin mutant with a progressive motor syndrome characterized by tremor, ataxia, immobility episodes, epilepsy and paralysis of the hind limbs. The rats show an initial hypomyelination, followed by a progressive demyelination of the central nervous system, but not peripheral nerves. All myelin alterations are due to an accumulation of microtubules in the cytoplasm and their process in oligodendrocytes, which disrupt the transporting mechanism from endoplasmic reticulum to Cis portion of the Golgi apparatus. Because of these microtubule alterations, all major myelin proteins decreased progressively. In fact, several brain regions of taiep rats showed an increment in the expression of glial fibrillary acidic protein (GFAP) suggesting glia activation. Additionally, when glial cells from taiep rats were cultured and exposed to lipopolysaccharide (LPS) or interferon gamma (IFN)-gamma, they produced higher amounts of nitrites and nitrates than control glial cells, suggesting an activation of glia cells in taiep rats. There are also an activation of interleukins and changes in their receptors that correlated with the progressive demyelination in this myelin mutant. The activation of immune responses in older rats correlated with the electrophysiological alterations such as changes in the sleep-wake pattern and absence seizures, or locomotion pattern and ataxia. Additionally, the frequency and mean duration of immobility episodes (IE's) increased after 6 month of age, which is an expression of rapid eye movement (REM) sleep alteration, suggesting that taiep rats suffer of narcolepsy-cataplexy. These results clearly showed that taiep rats are suitable model of neuro-immune alterations associated to chronic demyelination, and it is alternative model to experimental allergic encephalomyelitis to study glia-neuron interaction. In conclusion, taiep rat showed progressive immunological, electrophysiological and behavioral alterations due to demyeli- nation associated with normal lifespan that allow us to do diverse studies from different approaches.

Dopaminergic D2-like agonists produce yawning in the myelin mutant taiep and Sprague–Dawley rats

Systemic administration of D2-like dopaminergic-receptor agonists increases yawning behavior. However, only a few studies have been done in animals with pathological conditions. The taiep rat is a myelin mutant with an initial hypomyelination followed by progressive demyelination, being the brainstem one of the most affected areas. In our experiments, we analyzed the effects of systemic administration of the D2-family agonists and antagonists on yawning behavior, and correlated them with the lipid myelin content in the brainstem and other areas in the central nervous system (CNS) in 8month old male taiep and Sprague–Dawley rats. Subjects were maintained under standard conditions in Plexiglas cages with a 12:12 light–dark cycle, lights on at 0700 and free access to rodent pellets and tap water. Drugs were freshly prepared injected ip at 0800 and subjects were observed for 60min. When antagonists were used it was administered 15min before the agonist. Sprague–Dawley and taiep rats significantly increased their yawning frequency after systemic injection of (−)-quinpirole hydrochloride, R(+)-7-Hydroxy-2-(dipropylamino)tetralin hydrobromide (7-OH-DPAT) or trans-(±)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano [4,3-b]-1,4-oxazin-9-ol hydrochloride ((±)-PD 128,907). Among D2-like agonists used higher effects are obtained with (−)-quinpirole. The effects caused by (−)-quinpirole can be reduced by (−)-sulpiride; and yawning caused by 7-OH-DPAT was decreased by tiapride only in taiep rats. In Sprague–Dawley only (−)-sulpiride is able to decrease (−)-quinpirole-caused yawning. In conclusion, dopaminergic D2-like agonists are still able to cause yawning despite the severe myelin loss in taiep rats. Similarly, patients with various CNS illnesses that affect myelin, such as stroke or multiple sclerosis, are able to yawn suggesting that trigger neurons are still able to command this innate behavior.

Nitric oxide production is associated to increased lipoperoxidation and active caspase-3 in demyelinated brain regions of the taiep rat

We previously showed that the increase in nitric oxide (NO) levels and NO synthase (NOS) expression correlate with the progression of reactive astrocytosis and demyelination in the brains of 6-month-old taiep rats. Increased levels of NO can result in high concentration of peroxynitrite and thus cause tissue damage, which consists of lipoperoxidation of the cytoplasmic membrane, such as the myelin, and of apoptotic and necrotic cell-death. On this basis, we studied whether the increased NO production is associated with lipoperoxidation and cell death in the cerebellum and brainstem over the age (1, 3, 6, and 8 months) of taiep rats. The results were compared with those obtained in matched Sprague-Dawley (SD) rats. We measured the levels of nitrites (NO production), malonyldialdehyde, and 4-hydroxyalkenal (lipoperoxidation) in brain tissue homogenates. The three NOS isoforms and cleaved caspase-3 were evaluated by using ELISA and immunostaining techniques. Our results showed that NO production and lipoperoxidation increased in the cerebellum and brainstem as the age of the taiep rats increased compared to SD rats. The overexpression of nNOS and iNOS were in the Purkinje cells, magnocellular neurons, and in oligodendrocytes, whereas the glial cells showed strong cleaved-caspase-3 immunoreactivity. In summary our results suggest that NO plays a role in the demyelination and cell death in the taiep rat.

A Missense Mutation in Myelin Oligodendrocyte Glycoprotein as a Cause of Familial Narcolepsy with Cataplexy

Narcolepsy is a rare sleep disorder characterized by excessive daytime sleepiness and cataplexy. Familial narcolepsy accounts for less than 10% of all narcolepsy cases. However, documented multiplex families are very rare and causative mutations have not been identified to date. To identify a causative mutation in familial narcolepsy, we performed linkage analysis in the largest ever reported family, which has 12 affected members, and sequenced coding regions of the genome (exome sequencing) of three affected members with narcolepsy and cataplexy. We successfully mapped a candidate locus on chromosomal region 6p22.1 (LOD score ¼ 3.85) by linkage analysis. Exome sequencing identified a missense mutation in the second exon of MOG within the linkage region. A c.398C>G mutation was present in all affected family members but absent in unaffected members and 775 unrelated control subjects. Transient expression of mutant myelin oligodendrocyte glycoprotein (MOG) in mouse oligodendrocytes showed abnormal subcellular localization, suggesting an altered function of the mutant MOG. MOG has recently been linked to various neuropsychiatric disorders and is considered as a key autoantigen in multiple sclerosis and in its animal model, experimental autoimmune encephalitis. Our finding of a pathogenic MOG mutation highlights a major role for myelin and oligodendrocytes in narcolepsy and further emphasizes glial involvement in neurodegeneration and neurobehavioral disorders. [corrected].