Mice deficient in carbonic anhydrase type 8 exhibit motor dysfunctions and abnormal calcium dynamics in the somatic region of cerebellar granule cells

• Mice deficient in CAR8 (waddles mice) display deficits in rota-rod performance.
• Cerebellar granule cells from waddles mice show altered calcium signaling.
• Alterations in calcium signaling are linked to the mGluR1-IP3 pathway.
• Ataxia in the waddles mice is due to acute and chronic effects of the mutation.

The waddles (wdl) mouse is characterized by a namesake “side-to-side” waddling gait due to a homozygous mutation of the Car8 gene. This mutation results in non-functional copies of the protein carbonic anhydrase type 8. Rota-rod testing was conducted to characterize the wdl mutations’ effect on motor output. Results indicated that younger homozygotes outperformed their older cohorts, an effect not seen in previous studies. Heterozygotes, which were thought to be free of motor impairment, displayed motor learning deficiencies when compared with wild type performance. Acute cerebellar slices were then utilized for fluorescent calcium imaging experiments, which revealed significant alterations in cerebellar granule cell somatic calcium signaling when exposed to glutamate. The contribution of GABAergic signaling to these alterations was also verified using bath application of bicuculline. Changes in somatic calcium signals were found to be applicable to an in vivo scenario by comparing group responses to electrical stimulation of afferent mossy fiber projections. Finally, intracellular calcium store function was also found to be altered by the wdl mutation when slices were treated with thapsigargin. These findings, taken together with previous work on the wdl mouse, indicate a widespread disruption in cerebellar circuitry hampering proper neuronal communication.

This is a depiction of the potential mechanisms by which mutation of carbonic anhydrase type 8 alters cerebellar granule cell physiology. Legend: AMPA = α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate, Ca2+ = ionic calcium, CAR8 = carbonic anhydrase type 8, GABA = gamma aminobutyric acid, IP3(R) = inositol 1,4,5-trisphosphate (receptor), mGluR1 = metabotropic glutamate receptor group 1, NMDA = N-methyl-d-asparate, PIP2 = phosphatidylinositol 4,5 bisphosphate.Figure optionsDownload high-quality image (212 K)Download as PowerPoint slide