Changes of motor abilities during ontogenetic development in Lurcher mutant mice

Twenty years of cerebellar degeneration research at the department of pathological physiology, faculty of medicine, Pilsen, Charles University

Mutant Lurcher mice represent an animal model of naturally occurring cerebellar degeneration. A gene mutation causes the demise of all Purkinje cells, as along with certain other types, as well as the functional elimination of the cerebellar cortex. Involvement in the research using this model of the C3H strain began at the Department of Physiology, UCL in 1995/96. It continued in scientific cooperation with other European laboratories where we obtained Lurcher mice of the B6CBA strain. The aim of the effort was first to identify the extent to which the cerebellum is involved in the higher nervous activity, i.e. cognitive and other functions. In that research, use was made of an entire array of methodological procedures to examine learning, memory, motor functions and emotional behavior. It was completed with an electrophysiological examination of the brain and special microscopic procedures. The results demonstrated that the cerebellum (aside from its traditional tasks) does in fact play a significant role in cognitive function, emotions, etc. It was further found that the neurodegenerative processes also affected the immune and endocrine functions, confirming the concept of the unity of the psycho-neuroendocrine-immune system. Surprisingly, despite their neurological impairment, the affected animals were able to learn to some extent and, make progress with physical training, improving not only their motor skills but also learning and memory, including deferring of signs of aging. These particular findings may prove useful for human medicine.

Transient cerebellar alterations during development prior to obvious motor phenotype in a mouse model of spinocerebellar ataxia type 6

KEY POINTS

Spinocerebellar ataxia type 6 (SCA6) is a midlife-onset neurodegenerative disease caused by a CACNA1A mutation; CACNA1A is also implicated in cerebellar development. We have previously shown that when disease symptoms are present in midlife in SCA6^84Q/84Q mice, cerebellar Purkinje cells spike with reduced rate and precision. In contrast, we find that during postnatal development (P10-13), SCA6^84Q/84Q Purkinje cells spike with elevated rate and precision. Although surplus climbing fibres are linked to ataxia in other mouse models, we found surplus climbing fibre inputs on developing (P10-13) SCA6^84Q/84Q Purkinje cells when motor deficits were not detected. Developmental alterations were transient and were no longer observed in weanling (P21-24) SCA6^84Q/84Q Purkinje cells. Our results suggest that changes in the developing cerebellar circuit can occur without detectable motor abnormalities, and that changes in cerebellar development may not necessarily persist into adulthood.

ABSTRACT

Although some neurodegenerative diseases are caused by mutations in genes that are known to regulate neuronal development, surprisingly, patients may not present disease symptoms until adulthood. Spinocerebellar ataxia type 6 (SCA6) is one such midlife-onset disorder in which the mutated gene, CACNA1A, is implicated in cerebellar development. We wondered whether changes were observed in the developing cerebellum in SCA6 prior to the detection of motor deficits. To address this question, we used a transgenic mouse with a hyper-expanded triplet repeat (SCA6^84Q/84Q ) that displays late-onset motor deficits at 7 months, and measured cerebellar Purkinje cell synaptic and intrinsic properties during postnatal development. We found that firing rate and precision were enhanced during postnatal development in P10-13 SCA6^84Q/84Q Purkinje cells, and observed surplus multiple climbing fibre innervation without changes in inhibitory input or dendritic structure during development. Although excess multiple climbing fibre innervation has been associated with ataxic symptoms in several adult transgenic mice, we observed no detectable changes in cerebellar-related motor behaviour in developing SCA6^84Q/84Q mice. Interestingly, we found that developmental alterations were transient, as both Purkinje cell firing properties and climbing fibre innervation from weanling-aged (P21-24) SCA6^84Q/84Q mice were indistinguishable from litter-matched control mice. Our results demonstrate that significant alterations in neuronal circuit development may be observed without any detectable behavioural read-out, and that early changes in brain development may not necessarily persist into adulthood in midlife-onset diseases.

From mice to men: lessons from mutant ataxic mice

Ataxic mutant mice can be used to represent models of cerebellar degenerative disorders. They serve for investigation of cerebellar function, pathogenesis of degenerative processes as well as of therapeutic approaches. Lurcher, Hot-foot, Purkinje cell degeneration, Nervous, Staggerer, Weaver, Reeler, and Scrambler mouse models and mouse models of SCA1, SCA2, SCA3, SCA6, SCA7, SCA23, DRPLA, Niemann-Pick disease and Friedreich ataxia are reviewed with special regard to cerebellar pathology, pathogenesis, functional changes and possible therapeutic influences, if any. Finally, benefits and limitations of mouse models are discussed.

Effect of dimethyl sulfoxide in cerebellar mutant Lurcher mice

DMSO has been many times described as harmless substance, beneficial in various diseases or pathological states, including brain injury or ischemia. Using Lurcher mutant mice suffering from genetically determined olivocerebellar degeneration and normal wild type mice, we examined the effect of DMSO on spontaneous motor activity and spatial learning and orientation ability. The acute effect of DMSO was studied in mice aged 3, 6, 9 and 22 weeks. DMSO treatment decreased spontaneous activity in the open field and swimming speed in the Morris water maze in both Lurcher mutant and wild type mice. While saline-treated Lurcher mice showed age-related decline of spatial memory in the Morris water maze in DMSO-treated ones such decline did not occur. The mechanism of the effect of DMSO remains unclear. A possible explanation could be modulation of the brain perfusion and metabolism in the aging brain. The improvement of learning ability could be also mediated by a tranquilizing effect of DMSO reducing stress-induced behavioral disinhibition which is supposed to interfere with learning process in Lurcher mutants. Future studies which would investigate DMSO effects in other models of neurodegenerative diseases are necessary to verify its potential therapeutic impact.

Long-term survival of solid embryonic cerebellar grafts in Lurcher mice

Lurcher mutant mice represent a natural model of olivocerebellar degeneration. They serve as a tool to study pathogenesis, the functional impact of the degeneration as well as therapeutic approaches. Wild type littermates are used as healthy controls. Neurotransplantation may be a promising method of therapy for neurodegenerative diseases. The aim of this work was to compare the long-term survival rate of the solid embryonic cerebellar graft in adult Lurcher mutant and wild type mice of the B6CBA strain and to assess the fundamental structural features of the graft. The graft was obtained from 12-day-old GFP mouse embryos. The brains of host mice were examined histologically 6 months after the transplantation. The graft was identified according to its GFP fluorescence. The graft presence and structure was assessed. The graft survived in all 14 Lurcher mice and in 12 of the 14 wild type mice. Cell migration and fibre sprouting from the graft were poor. No marked differences in the graft morphology between Lurcher mutant and wild type mice were found. The graft survival and appearance were similar to those after a shorter period described in a previous study. This suggests that during the 6 months, no intensive or commonly occurring processes changing the graft had proceeded and that the Lurcher mutant cerebellum niche had no strong influence over the fate of the solid cerebellar graft.