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

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.

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.

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.