Differential regulation of Purkinje cell dendritic spines in rolling mouse Nagoya (tg/tg), P/Q type calcium channel (α1(A)/Ca(v)2.1) mutant.

Voltage dependent calcium channels (VDCC) participate in regulation of neuronal Ca(2+). The Rolling mouse Nagoya (Cacna1a(tg-rol)) is a spontaneous P/Q type VDCC mutant, which has been suggested as an animal model for some human neurological diseases such as autosomal dominant cerebellar ataxia (SCA6), familial hemiplegic migraine and episodic ataxia type-2. Morphology of Purkinje cell (PC) dendritic spine is suggested to be regulated by signal molecules such as Ca(2+) and by interactions with afferent inputs. The amplitude of excitatory postsynaptic current was decreased in parallel fiber (PF) to PC synapses, whereas apparently increased in climbing fiber (CF) to PC synapses in rolling mice Nagoya. We have studied synaptic morphology changes in cerebella of this mutant strain. We previously found altered synapses between PF varicosity and PC dendritic spines. To study dendritic spine plasticity of PC in the condition of insufficient P/Q type VDCC function, we used high voltage electron microscopy (HVEM). We measured the density and length of PC dendritic spines at tertiary braches. We observed statistically a significant decrease in spine density as well as shorter spine length in rolling mice compared to wild type mice at tertiary dendritic braches. In proximal PC dendrites, however, there were more numerous dendritic spines in rolling mice Nagoya. The differential regulation of rolling PC spines at tertiary and proximal dendrites in rolling mice Nagoya suggests that two major excitatory afferent systems may be regulated reciprocally in the cerebellum of rolling mouse Nagoya.

Altered neuronal nitric oxide synthase expression in the cerebellum of calcium channel mutant mice.

Tottering, rolling Nagoya, and leaner mutant mice all exhibit cerebellar ataxia to varying degrees, from mild (tottering mice) to severe (leaner mice). Collectively, these mice are regarded as tottering locus mutants because each of these mutant mice expresses a different autosomal recessive mutation in the gene coding for the alpha(1A) calcium ion channel protein, which is the pore forming subunit for P/Q-type high voltage activated calcium ion channels. These mutant mice all exhibit varying degrees of cerebellar dysfunction and neuronal cell death. Nitric oxide (NO) is an important messenger molecule in the central nervous system, especially in the cerebellum, and it is produced via the enzyme, nitric oxide synthase (NOS). We investigated expression of neuronal-NOS (n-NOS) in the cerebella of all three mutant mice, as revealed by NADPH-diaphorase (NADPH-d) histochemical staining, quantitation of n-NOS protein using Western blotting and quantitation of n-NOS mRNA using in situ hybridization. The expression of n-NOS mRNA and protein as well as the NADPH-d histochemical reaction were elevated in tottering and rolling Nagoya cerebella. n-NOS mRNA and the NADPH-d histochemical reaction were decreased in the leaner cerebellum, but the leaner mouse n-NOS protein concentration was not significantly different compared to age- and gender-matched controls. These findings suggest that NO may act as an important mediator in the production of the neuropathology observed in these mutant mice.

Apoptotic cell death of cerebellar granule cells in rolling mouse Nagoya.

Rolling mouse Nagoya is a voltage dependent calcium channel alpha1A subunit mutant showing moderate ataxia. Granule cell loss was previously reported in the cerebellar vermis of homozygous rolling. Apoptotic cerebellar granule cell death was reported in homozygous leaner mice, an allele of rolling. Cerebella of 21-day-old rolling and wild type mice were used for terminal dUTP nick-end-labeling (TUNEL) assay and electron microscopic observation to understand the mechanism of granule cell loss in rolling mice. The number of TUNEL-positive cells was significantly increased in rolling. More TUNEL-positive cells were observed in the anterior cerebellar vermis compared with posterior. Condensation and fragmentation of granule cell nuclei in rolling mouse were observed frequently. These results suggest that apoptosis is one of the mechanisms of granule cell loss in the rolling cerebellum.