Proceedings of The Physiological Society
King's College London (2011) Proc Physiol Soc 22, PC17
Cannabinoid CB1 receptor-mediated signalling in the ducky2J model of cerebellar ataxia
X. Wang1, B. J. Whalley1, G. J. Stephens1
1. School of Pharmacy, University of Reading, Reading, United Kingdom.
The ducky2J (du2J) mutation causes expression of a truncated, non-functional alpha2delta-2 Ca2+ channel subunit to provide a model of cerebellar ataxia and absence seizures. Du2J mutants have been shown to exhibit altered spontaneous Purkinje cell activity (Donato et al., 2006). It is also known that activation of cannabinoid CB1 receptors (CB1Rs) can induce cerebellar dysfunction, causing severe motor incoordination, including forms of ataxia (Patel & Hillard, 2001). Therefore, we have investigated CB1R-mediated modulation of cerebellar neuronal activity in the ducky2J model. Electrophysiological data were acquired via multi-electrode array (MEA) and whole cell patch clamp in acute cerebellar slices from wild type (+/+) and heterozygous (+/du2J) mice (male; 3-5 weeks old). Data are expressed as % of control; statistical significance was determined by Friedman tests followed by Dunn’s tests unless stated. In +/+ mice, MEA recordings from the Purkinje cell layer (PCL) showed that the CBR agonist WIN55,212-2 (WIN55; 5μM) significantly increased firing rate (130 ± 8%; P<0.05); subsequent addition of AM251 (2μM) decreased PC firing rate (98 ± 7%; P<0.001 vs WIN55). In +/+ mice, the firing rate of granule cell layer (GCL) neurones were unaffected by 5μM WIN55 and 2μM AM251 (both P>0.05). These data are consistent with CB1R regulation of presynaptic inputs onto Purkinje cells, but not granule cells, in wild-type mouse cerebellum. Whole cell patch clamp recording from PCs in +/+ mice confirmed CB1R ligand effects in +/+ mice, whereby AM251 increased inhibitory postsynaptic (IPSC) frequency (P<0.01; Repeated one-way ANOVA followed by Tukey test ); these data are also consistent with a localization of CB1R to inhibitory presynaptic terminals onto PCs (Ma et al., 2008; Wang et al., 2011). In +/du2J mice, WIN55 (5μM) and AM251 (2μM) had no effect on in PCL firing rate; these CB1R ligands also had no effect on GCL firing rate. These data point to differential CB1R regulation of presynaptic inputs onto Purkinje cells between wild-type and +/du2J mutant mouse cerebellum. In whole cell patch clamp recording from PCs in +/du2J mice, WIN55 (5μM) and AM251 (2μM) had no effect on IPSC frequency. Taken together, these results suggest that CB1 receptor mediated signalling is compromised in du2J mutant mice. It will be of interest to determine if aberrant endocannabinoid signalling underlies an ataxic phenotype.
Where applicable, experiments conform with Society ethical requirements