Preserved otolith organ function in caspase-3-deficient mice with impaired horizontal semicircular canal function.

Genetically engineered mice are valuable models for elucidation of auditory and vestibular pathology. Our goal was to establish a comprehensive vestibular function testing system in mice using: (1) horizontal angular vestibulo-ocular reflex (hVOR) to evaluate semicircular canal function and (2) otolith-ocular reflex (OOR) to evaluate otolith organ function and to validate the system by characterizing mice with vestibular dysfunction. We used pseudo off-vertical axis rotation to induce an otolith-only stimulus using a custom-made centrifuge. For the OOR, horizontal slow-phase eye velocity and vertical eye position were evaluated as a function of acceleration. Using this system, we characterized hVOR and OOR in the caspase-3 (Casp3) mutant mice. Casp3 (-/-) mice had severely impaired hVOR gain, while Casp3 (+/-) mice had an intermediate response compared to WT mice. Evaluation of OOR revealed that at low-to-mid frequencies and stimulus intensity, Casp3 mutants and WT mice had similar responses. At higher frequencies and stimulus intensity, the Casp3 mutants displayed mildly reduced otolith organ-related responses. These findings suggest that the Casp3 gene is important for the proper function of the semicircular canals but less important for the otolith organ function.

Loss of α-calcitonin gene-related peptide (αCGRP) reduces the efficacy of the Vestibulo-ocular Reflex (VOR).

The neuroactive peptide calcitonin-gene related peptide (CGRP) is known to act at efferent synapses and their targets in hair cell organs, including the cochlea and lateral line. CGRP is also expressed in vestibular efferent neurons as well as a number of central vestibular neurons. Although CGRP-null (-/-) mice demonstrate a significant reduction in cochlear nerve sound-evoked activity compared with wild-type mice, it is unknown whether and how the loss of CGRP influence vestibular system function. Vestibular function was assessed by quantifying the vestibulo-ocular reflex (VOR) in alert mice. The loss of CGRP in (-/-) mice was associated with a reduction of the VOR gain of ≈50% without a concomitant change in phase. Using immunohistochemistry, we confirmed that, although CGRP staining was absent in the vestibular end-organs of null (-/-) mice, cholinergic staining appeared normal, suggesting that the overall gross development of vestibular efferent innervation was unaltered. We further confirmed that the observed deficit in vestibular function of null (-/-) mice was not the result of nontargeted effects at the level of the extraocular motor neurons and/or their innervation of extraocular muscles. Analysis of the relationship between vestibular quick phase amplitude and peak velocity revealed that extraocular motor function was unchanged, and immunohistochemistry revealed no abnormalities in motor endplates. Together, our findings show that the neurotransmitter CGRP plays a key role in ensuring VOR efficacy.

A cerebellar learning model of vestibulo-ocular reflex adaptation in wild-type and mutant mice.

Mechanisms of cerebellar motor learning are still poorly understood. The standard Marr-Albus-Ito theory posits that learning involves plasticity at the parallel fiber to Purkinje cell synapses under control of the climbing fiber input, which provides an error signal as in classical supervised learning paradigms. However, a growing body of evidence challenges this theory, in that additional sites of plasticity appear to contribute to motor adaptation. Here, we consider phase-reversal training of the vestibulo-ocular reflex (VOR), a simple form of motor learning for which a large body of experimental data is available in wild-type and mutant mice, in which the excitability of granule cells or inhibition of Purkinje cells was affected in a cell-specific fashion. We present novel electrophysiological recordings of Purkinje cell activity measured in naive wild-type mice subjected to this VOR adaptation task. We then introduce a minimal model that consists of learning at the parallel fibers to Purkinje cells with the help of the climbing fibers. Although the minimal model reproduces the behavior of the wild-type animals and is analytically tractable, it fails at reproducing the behavior of mutant mice and the electrophysiology data. Therefore, we build a detailed model involving plasticity at the parallel fibers to Purkinje cells' synapse guided by climbing fibers, feedforward inhibition of Purkinje cells, and plasticity at the mossy fiber to vestibular nuclei neuron synapse. The detailed model reproduces both the behavioral and electrophysiological data of both the wild-type and mutant mice and allows for experimentally testable predictions.

Similar phenotypes caused by mutations in OTOG and OTOGL.

OBJECTIVES: Recently, OTOG and OTOGL were identified as human deafness genes. Currently, only four families are known to have autosomal recessive hearing loss based on mutations in these genes. Because the two genes code for proteins (otogelin and otogelin-like) that are strikingly similar in structure and localization in the inner ear, this study is focused on characterizing and comparing the hearing loss caused by mutations in these genes. DESIGN: To evaluate this type of hearing, an extensive set of audiometric and vestibular examinations was performed in the 13 patients from four families. RESULTS: All families show a flat to downsloping configuration of the audiogram with mild to moderate sensorineural hearing loss. Speech recognition scores remain good (>90%). Hearing loss is not significantly different in the four families and the psychophysical test results also do not differ among the families. Vestibular examinations show evidence for vestibular hyporeflexia. CONCLUSION: Because otogelin and otogelin-like are localized in the tectorial membrane, one could expect a cochlear conductive hearing loss, as was previously shown in DFNA13 (COL11A2) and DFNA8/12 (TECTA) patients. Results of psychophysical examinations, however, do not support this. Furthermore, the authors conclude that there are no phenotypic differences between hearing loss based on mutations in OTOG or OTOGL. This phenotype description will facilitate counseling of hearing loss caused by defects in either of these two genes.

Clinical characterization of a novel COCH mutation G87V in a Chinese DFNA9 family.

OBJECTIVES: To characterize the clinical features of a Chinese DFNA9 family associated with a novel COCH mutation and to confirm the proposed genotype-phenotype correlation of COCH. METHODS: Mutation screening of 79 deafness genes was performed in the proband by targeted next-generation sequencing. Co-segregation of the disease phenotype and the detected variants was confirmed in all family members by PCR amplification and Sanger sequencing. The progression of hearing impairment in affected family members was followed and the concomitant vestibular dysfunction was verified by the caloric vestibulo-ocular reflex test. RESULTS: A novel COCH mutation p.G87V was identified in the family segregating with late-onset, progressive sensorineural hearing impairment and consistent vestibular dysfunction. CONCLUSION: The p.G87V mutation leads to a very similar phenotype as a previously reported p.G87W mutation of COCH. Our study suggested that the G87 residue is critical for function of COCH and further confirms a previously proposed genotype-phenotype correlation for DFNA9.

Retinoic acid deficiency impairs the vestibular function.

The retinaldehyde dehydrogenase 3 (Raldh3) gene encodes a major retinoic acid synthesizing enzyme and is highly expressed in the inner ear during embryogenesis. We found that mice deficient in Raldh3 bear severe impairment in vestibular functions. These mutant mice exhibited spontaneous circling/tilted behaviors and performed poorly in several vestibular-motor function tests. In addition, video-oculography revealed a complete loss of the maculo-ocular reflex and a significant reduction in the horizontal angular vestibulo-ocular reflex, indicating that detection of both linear acceleration and angular rotation were compromised in the mutants. Consistent with these behavioral and functional deficiencies, morphological anomalies, characterized by a smaller vestibular organ with thinner semicircular canals and a significant reduction in the number of otoconia in the saccule and the utricle, were consistently observed in the Raldh3 mutants. The loss of otoconia in the mutants may be attributed, at least in part, to significantly reduced expression of Otop1, which encodes a protein known to be involved in calcium regulation in the otolithic organs. Our data thus reveal a previously unrecognized role of Raldh3 in structural and functional development of the vestibular end organs.

Variable degrees of hearing impairment in a Dutch DFNX4 (DFN6) family.

OBJECTIVE: Investigation of the audiometric characteristics of a large Dutch DFNX4 family with a p.Glu72X mutation in the SMPX gene. PATIENTS AND METHODS: Sixty family members participated in this study and examination consisted of medical history, otoscopy, pure tone and speech audiometry. Linkage and mutation analysis revealed a pathogenic mutation in the SMPX gene. RESULTS: All 25 mutation carriers exhibited hearing impairment, except one woman aged 25 years. The men (n = 10) showed more severe hearing impairment than the women (n = 14) and already at a younger age. The age of onset according to history was 2-10 years (mean: 3.3 years) in men and 3-48 years (mean: 26.4 years) in women. In the men, severe threshold deterioration mainly occurred during the first two decades of life, especially at the higher frequencies. The women showed milder threshold deterioration and more pronounced across-subjects and individual inter-aural variation, especially at 2-8 kHz. Longitudinal linear regression analysis demonstrated significant progression of at least two frequencies in five individuals (3 men and 2 women). The speech recognition scores of the mutation carriers with hearing impairment were decreased at relatively young ages compared to a reference group of patients with only presbycusis, especially in men. However, all these patients tended to have better speech recognition scores than the presbycusis patients at matching PTA(1,2,4 kHz) levels. CONCLUSION: This study demonstrates the phenotypic heterogeneity in this large family with an X-linked pattern of inherited sensorineural hearing impairment. The men showed more severe hearing impairment at a younger age with more pronounced progression during the first two decades of life, while women demonstrated less severe hearing impairment with more gradual progression and a wider variation in age of onset, degree of hearing impairment and inter-aural asymmetry in thresholds.

Audiometric characteristics of a Dutch family with Muckle-Wells syndrome.

Description of the audiometric and vestibular characteristics of a Dutch family with Muckle-Wells syndrome (MWS). Examination of all family members consisted of pure tone audiometry, otoscopy and genetic analysis. In addition, a selected group underwent speech audiometry, vestibulo-ocular examination, acoustic reflex testing and tests assessing loudness scaling, gap detection, difference limen for frequency and speech perception in noise. Linear regression analyses were performed on the audiometric data. Six clinically affected family members participated in this study and all were carriers of a p.Tyr859His mutation in the NLPR3 gene. Most affected family members reported bilateral, slowly progressive hearing impairment since childhood. Hearing impairment started at the high frequencies and the low- and mid-frequency threshold values deteriorated with advancing age. Annual threshold deterioration (ATD) ranged from 1.3 to 1.9 dB/year with the highest values at the lower frequencies. Longitudinal linear regression analysis demonstrated significant progression for a number of frequencies in five individuals. Speech recognition scores were clearly affected. However, these individuals tended to have higher speech recognition scores than presbyacusis patients at similar PTA(1,2,4 kHz) levels. The loudness growth curves were steeper than those found in individuals with normal hearing, except for one family member (individual IV:6). Suprathreshold measurements, such as difference limen for frequency (DL(f)), gap detection and particularly speech perception in noise were within the normal range or at least close to data obtained in two groups of patients with a so-called conductive type of hearing loss, situated in the cochlea. Hearing impairment in MWS is variable and shows resemblance to previously described intra-cochlear conductive hearing impairment. This could be helpful in elucidating the pathogenesis of hearing impairment in MWS. Other associated symptoms of MWS were mild and nonspecific in the present family. Therefore, even without any obvious syndromic features, MWS can be the cause of sensorineural hearing impairment, especially when combined with (mild) skin rash and musculoskeletal symptoms. An early diagnosis of MWS is essential to prevent irreversible damage from amyloidosis. The effect of IL-1ß inhibitors on hearing impairment is more controversial, but an early start of treatment seems to be essential. Therefore, our results are of importance in patient care and counselling.

The clinical and molecular genetic features of idiopathic infantile periodic alternating nystagmus.

Periodic alternating nystagmus consists of involuntary oscillations of the eyes with cyclical changes of nystagmus direction. It can occur during infancy (e.g. idiopathic infantile periodic alternating nystagmus) or later in life. Acquired forms are often associated with cerebellar dysfunction arising due to instability of the optokinetic-vestibular systems. Idiopathic infantile periodic alternating nystagmus can be familial or occur in isolation; however, very little is known about the clinical characteristics, genetic aetiology and neural substrates involved. Five loci (NYS1-5) have been identified for idiopathic infantile nystagmus; three are autosomal (NYS2, NYS3 and NYS4) and two are X-chromosomal (NYS1 and NYS5). We previously identified the FRMD7 gene on chromosome Xq26 (NYS1 locus); mutations of FRMD7 are causative of idiopathic infantile nystagmus influencing neuronal outgrowth and development. It is unclear whether the periodic alternating nystagmus phenotype is linked to NYS1, NYS5 (Xp11.4-p11.3) or a separate locus. From a cohort of 31 X-linked families and 14 singletons (70 patients) with idiopathic infantile nystagmus we identified 10 families and one singleton (21 patients) with periodic alternating nystagmus of which we describe clinical phenotype, genetic aetiology and neural substrates involved. Periodic alternating nystagmus was not detected clinically but only on eye movement recordings. The cycle duration varied from 90 to 280 s. Optokinetic reflex was not detectable horizontally. Mutations of the FRMD7 gene were found in all 10 families and the singleton (including three novel mutations). Periodic alternating nystagmus was predominantly associated with missense mutations within the FERM domain. There was significant sibship clustering of the phenotype although in some families not all affected members had periodic alternating nystagmus. In situ hybridization studies during mid-late human embryonic stages in normal tissue showed restricted FRMD7 expression in neuronal tissue with strong hybridization signals within the afferent arms of the vestibulo-ocular reflex consisting of the otic vesicle, cranial nerve VIII and vestibular ganglia. Similarly within the afferent arm of the optokinetic reflex we showed expression in the developing neural retina and ventricular zone of the optic stalk. Strong FRMD7 expression was seen in rhombomeres 1 to 4, which give rise to the cerebellum and the common integrator site for both these reflexes (vestibular nuclei). Based on the expression and phenotypic data, we hypothesize that periodic alternating nystagmus arises from instability of the optokinetic-vestibular systems. This study shows for the first time that mutations in FRMD7 can cause idiopathic infantile periodic alternating nystagmus and may affect neuronal circuits that have been implicated in acquired forms.

Vestibular function in families with inherited autosomal dominant hearing loss.

The inner ear contains the developmentally related cochlea and peripheral vestibular labyrinth. Given the similar physiology between these two organs, hearing loss and vestibular dysfunction may be expected to occur simultaneously in individuals segregating mutations in inner ear genes. Twenty-two different genes have been discovered that when mutated lead to non-syndromic autosomal dominant hearing loss. A review of the literature indicates that families segregating mutations in 13 of these 22 genes have undergone formal clinical vestibular testing. Formal assessment revealed vestibular dysfunction in families with mutations in ten of these 13 genes. Remarkably, only families with mutations in the COCH and MYO7A genes self-report considerable vestibular challenges. Families segregating mutations in the other eight genes do not self-report significant balance problems and appear to compensate well in everyday life for vestibular deficits discovered during formal clinical vestibular assessment. An example of a family (referred to as the HL1 family) with progressive hearing loss and clinically-detected vestibular hypofunction that does not report vestibular symptoms is described in this review. Notably, one member of the HL1 family with clinically-detected vestibular hypofunction reached the summit of Mount Kilimanjaro.

Asymmetric recovery in cerebellar-deficient mice following unilateral labyrinthectomy.

The term "vestibular compensation" refers to the resolution of motor deficits resulting from a peripheral vestibular lesion. We investigated the role of the cerebellum in the compensation process by characterizing the vestibuloocular reflex (VOR) evoked by head rotations at frequencies and velocities similar to those in natural behaviors in wild-type (WT) versus cerebellar-deficient Lurcher (Lc/+) mice. We found that during exploratory activity, normal mice produce head rotations largely consisting of frequencies < or =4 Hz and velocities and accelerations as large as 400 degrees/s and 5,000 degrees/s2, respectively. Accordingly, the VOR was characterized using sinusoidal rotations (0.2-4 Hz) as well as transient impulses (approximately 400 degrees/s; approximately 2,000 degrees/s2). Before lesions, WT and Lc/+ mice produced similar VOR responses to sinusoidal rotation. Lc/+ mice, however, had significantly reduced gains for transient stimuli. After unilateral labyrinthectomy, VOR recovery followed a similar course for WT and Lc/+ groups during the first week: gain was reduced by 80% for ipsilesionally directed head rotations on day 1 and improved for both strains to values of approximately 0.4 by day 5. Moreover, responses evoked by contralesionally directed rotations returned to prelesion in both strains within this period. However, unlike WT, which showed improving responses to ipsilesionally directed rotations, recovery plateaued after first week for Lc/+ mice. Our results show that despite nearly normal recovery in the acute phase, long-term compensation is compromised in Lc/+. We conclude that cerebellar pathways are critical for long-term restoration of VOR during head rotation toward the lesioned side, while noncerebellar pathways are sufficient to restore proper gaze stabilization during contralesionally directed movements.

Periodic alternating nystagmus and periodic alternating skew deviation in spinocerebellar ataxia type 6.

The combination of periodic alternating nystagmus (PAN) and periodic alternating skew deviation (PASD) is rare. We report a case of PAN and PASD in a patient with spinocerebellar ataxia type 6 (SCA-6) and discuss the role of the cerebellum as a plausible mechanism for this combined pathologic condition.

Spinocerebellar ataxia type 17 (SCA17): oculomotor phenotype and clinical characterization of 15 Italian patients.

SCA17 is a rare type of autosomal dominant spinocerebellar ataxia caused by a CAG/CAA expansion in the gene encoding the TATA-binding protein (TBP). We screened for triplet expansion in the TBP gene 110 subjects with progressive cerebellar ataxia and 94 subjects with Huntington-like phenotype negative at specific molecular tests. SCA17 mutation-positive subjects were found in both groups of patients. Expanded alleles with > or = 44 CAG/CAA repeats were identified in 11 individuals and in 4 non-symptomatic relatives. Eleven de novo diagnosed patients and four patients previously reported underwent extensive clinical, neuroradiological and oculographic examination. Cerebellar signs and symptoms were present in all cases; 80% of the patients had mild to severe cognitive deficits; 66% of patients showed choreic movements; pyramidal signs, bradykinesia and dystonia were observed in approx 50% of the cases. MRI demonstrated cortical and cerebellar atrophy in all patients, whereas neurophysiological examination excluded signs of peripheral nervous system involvement. Oculographic examinations were performed in 9 out of 15 patients and showed a distinct pattern of oculomotor abnormalities, characterized by impairment of smooth pursuit, defects in the saccade accuracy, normal saccade velocity, hyperreflexia of vestibuloocular reflexes, and absence of nystagmus. In summary, this study presents one of the largest series of SCA17 patients in Europe. In our group of patients, SCA17 represents the third most frequent SCA genotype. Our clinical data confirm the large variability in SCA17 phenotypic presentation, and indicate that a peculiar combination of neuroradiological, electrophysiological and oculomotor findings is recognizable in SCA17.

Ozzy, a Jag1 vestibular mouse mutant, displays characteristics of Alagille syndrome.

The mouse mutant Ozzy, originating from an ENU-mutagenesis programme, displays a head bobbing phenotype. We report here that Ozzy mice show a clear deficit in vestibulo-ocular reflex (VOR). Micro-CT scanning of the inner ears showed narrowing and truncations of at least one of the semicircular canals and loss of the ampullae. Frequency-specific auditory-evoked brainstem response (ABR) tests revealed a slight threshold increase in the middle frequency range compared to wild-type littermates. Linkage analysis localised the gene in a 5.5-cM region on chromosome 2. Subsequently, a 499 T-->A missense mutation was identified in Jag1, leading to a substitution of an evolutionary conserved tryptophane (W167R). Mutations in the human homologue of Jag1 cause Alagille syndrome (AGS), an autosomal dominant disorder associated with liver, heart, eye and skeletal abnormalities, accompanied by a characteristic facies. In human patients, it occasionally affects other organ systems like the kidney or the inner ear. Liver disease is the main diagnostic factor for AGS. Ozzy mice showed significantly less intrahepatic bile ducts than wild-type littermates. Thirty-seven percent of Ozzy mice showed heart defects. No eye or vertebral abnormalities could be detected. In conclusion, Ozzy mice show two of the major and one minor characteristic of AGS.

Locomotor and oculomotor impairment associated with cerebellar dysgenesis in Zic3-deficient (Bent tail) mutant mice.

We examined the adult neural phenotypes of the Bent tail mutant mouse. The Bent tail mutant mouse was recently shown to lack a submicroscopic part of the X chromosome containing the Zic3 gene, which encodes a zinc-finger protein controlling vertebrate neural development. While nearly one-fourth of hemizygous Bent tail (Bn/Y, Zic3-deficient) mice developed neural tube defects in their midbrain and hindbrain region, the other Bn/Y mice showed apparently normal behaviour in a C57BL/6 genetic background. A battery of behavioural and eye movement tests revealed impaired spontaneous locomotor activity, reduction of muscle tone and impairments of vestibuloocular and optokinetic eye movements in these mice. Morphological examination of the mutant brain showed a significant reduction in the cell numbers in the cerebellar anterior lobe and paraflocculus-flocculus complex. Our results indicate that the cerebellar dysgenesis characterized by subregional hypoplasia affects the locomotor activity, muscle tone and eye movement control of the mice. These findings may have some clinical implications in relation to disorders characterized by cerebellar dysgenesis, such as Joubert syndrome.

Impairment of LTD and cerebellar learning by Purkinje cell-specific ablation of cGMP-dependent protein kinase I.

The molecular basis for cerebellar plasticity and motor learning remains controversial. Cerebellar Purkinje cells (PCs) contain a high concentration of cGMP-dependent protein kinase type I (cGKI). To investigate the function of cGKI in long-term depression (LTD) and cerebellar learning, we have generated conditional knockout mice lacking cGKI selectively in PCs. These cGKI mutants had a normal cerebellar morphology and intact synaptic calcium signaling, but strongly reduced LTD. Interestingly, no defects in general behavior and motor performance could be detected in the LTD-deficient mice, but the mutants exhibited an impaired adaptation of the vestibulo-ocular reflex (VOR). These results indicate that cGKI in PCs is dispensable for general motor coordination, but that it is required for cerebellar LTD and specific forms of motor learning, namely the adaptation of the VOR.

The vestibulo ocular reflex (VOR) in otoconia deficient head tilt (het) mutant mice versus wild type C57BL/6 mice.

The horizontal and vertical vestibulo ocular reflex (VOR) of head tilted (het) mutant mice was compared to C57BL/6 controls. Eye movements were recorded in darkness using a temporarily attached search coil. Contributions of semicircular canal versus otolith organ signals were investigated by providing a canal only (vertical axis) or canal plus otolith organ (horizontal axis) stimulus. In controls, rotations that stimulated only the canals (upright yaw and on tail roll) produced accurate VOR timing during middle frequency rotations at 0.5 Hz (gain 0.27, phase error 6 degrees), and a phase advanced VOR during low frequency rotations at 0.05 Hz (0.05, 115 degrees). In het mutant mice, these rotations produced a highly attenuated VOR response and phase errors at both 0.5 Hz (0.11, 42 degrees) and 0.05 Hz (0.01, 36 degrees). In controls, rotations that stimulated both the otolith organs and semicircular canals (upright roll and on tail yaw) produced higher VOR gains overall than were elicited during vertical axis rotations, with phase accurate VOR at both 0.5 Hz (0.52, 4 degrees) and 0.05 Hz (0.34, 9 degrees). In het mutant mice, these rotations produced a highly attenuated VOR response and phase errors at both 0.5 Hz (0.14, 51 degrees) and 0.05 Hz (0.01, 43 degrees). During constant velocity rotations about an earth horizontal axis, eye velocity bias and modulation were virtually absent in het mutant mice, while robust in controls. Control mice produced compensatory ocular deviations in response to static head tilt, but responses in het mice were weak and inconsistent. These results show that het mice not only lack all aspects of otolith mediated VOR, but also are deficient in canal mediated VOR. Because semicircular canals are normal in het mice, we conclude that central neurons of the canal VOR are dependent on otolith organ signals for normal performance.

Familial vestibulocerebellar disorder maps to chromosome 13q31-q33: a new nystagmus locus.

PURPOSE: To determine a gene locus for a family with a dominantly inherited vestibulocerebellar disorder characterised by early onset, but not congenital nystagmus. DESIGN: Observational and experimental study. METHODS: We carried out a phenotypic study of a unique four generation family with nystagmus. We performed genetic linkage studies including a genome wide search. RESULTS: Affected family members developed vestibulocerebellar type nystagmus in the first two years of life. A higher incidence of strabismus was noted in affected members. Haplotype construction and analysis of recombination events linked the disorder to a locus (NYS4) on chromosome 13q31-q33 with a lod score of 6.322 at theta=0 for D13S159 and narrowed the region to a 13.8 cM region between markers D13S1300 and D13S158. CONCLUSIONS: This study suggests that the early onset acquired nystagmus seen in this family is caused by a single gene defect. Identification of the gene may hold the key to understanding pathways for early eye stabilisation and strabismus.

Cerebellar LTD facilitates but is not essential for long-term adaptation of the vestibulo-ocular reflex.

The induction of cerebellar long-term depression (LTD) at the parallel fibre-Purkinje cell synapse is selectively blocked in L7-PKCi transgenic mice, rendering these mice unable to adaptively modify their vestibulo-ocular reflex (VOR) during visuo-vestibular training for a few hours. Despite this deficit, their eye movement performance as well as their general motor behaviour appears unaffected. This combination suggests that, in the long term, residual forms of plasticity in the vestibulo-cerebellar circuitry can compensate for the absence of cerebellar LTD. To investigate whether LTD-deficient mice exhibit motor learning in the long run, we subjected L7-PKCi transgenic mice to visuo-vestibular training paradigms that were aimed at either increasing or decreasing the VOR response in the course of eight consecutive days. During the increasing paradigm, the VOR gain of transgenic mice increased significantly, while VOR gain decreased and VOR phase-lead increased during the decreasing paradigm. The impact of these long training periods on the VOR was significantly smaller in LTD-deficient mice than in wild type littermates. Thus, while LTD may be necessary for short-term VOR adaptation, it facilitates but is not required for long-term adaptation of the VOR.