Strain-Specific Regulation of Striatal Phenotype in Drd2-eGFP BAC Transgenic Mice
C. Savio Chan, Jayms D. Peterson, Tracy S. Gertler, Kelly E. Glajch, Ruth E. Quintana, Qiaoling Cui, Luke E. Sebel, Joshua L. Plotkin, Weixing Shen, Myriam Heiman, Nathaniel Heintz, Paul Greengard and D. James Surmeier
Journal of Neuroscience 4 July 2012, 32 (27) 9124-9132; DOI: https://doi.org/10.1523/JNEUROSCI.0229-12.2012
Drd2-eGFP BAC transgenic mice display modest alterations in gene expression that are strain and zygosity specific. qPCR analyses were performed on Drd2-GFP BAC mice of different genetic backgrounds and zygosity. Gene expression levels are presented relative to their respective wild-type controls. Multiple reference genes (Atp5b, Cyc1, Eef1e1, Gapdh, Gusb, H2afz, Hmbs, Sdha, and Uchl1) were included in the analyses to account for the differential transcript expression across mouse groups. Target genes with important functions in the striatum were chosen for expression analysis. Ttc12 is a passenger gene included in the Drd2-eGFP BAC construct. Note that Drd2 and Ttc12 expression were differentially regulated across different mouse groups.
The dichotomy in the intrinsic properties of striatal SPNs is preserved in the Drd2-eGFP BAC transgenic mice. A–E, Left, Sample current-clamp recordings showing differences in the excitability of dSPNs and iSPNs in brain slices from different strains of mice of varying zygosity for the BAC transgene. Right, Pooled frequency–current plots for each condition. Note the clear dichotomy in excitability except in the case of SW mice.
Synaptic properties of corticostriatal input to SPNs are not altered by Drd2-eGFP BAC transgene. Physiological and anatomical properties of corticostriatal iSPNs from hemizygous and homozygous Drd2-eGFP BAC transgenic on an FVB/N background were measured. A, Corticostriatal glutamatergic synaptic responses in iSPNs evoked by paired-pulse electrical stimulation (delivered at 50 Hz) at the times shown at the bottom. Right, Box plot of paired-pulse ratios from the two genotypes revealed the responses were identical. B, Representative traces of mEPSCs in iSPNs. No difference in the frequency or amplitude of mEPSCs was noted, as shown in box plots on the right. C, Two-photon spine imaging of iSPNs in brain slices from Drd2-eGFP BAC transgenic mice. No significant difference in the spine density was found as shown by the box plot on the right.
Intrinsic excitability of spiny projection neurons was regulated by dopamine. A, Top, Representative current-clamp recordings showing the membrane potential of naive iSPNs in response to somatic current injection. Bottom, Frequency–current plots revealed a decrease (rightward shift) in iSPN excitability following chronic 6-OHDA lesions. The effect of subchronic Drd2 receptor blockade on the intrinsic excitability (dotted lines) was similar in iPSNs to that seen following 6-OHDA lesion. B, Representative current-clamp recordings showing the membrane potential of iSPNs from 6-OHDA-lesioned and eticlopride-treated animals.
Ambulatory activity was unaltered in hemizygous Drd2-eGFP mice. A, Heat maps derived from the total number of crossing across the open field within a 20 min testing session. Data were averaged between animals from the same cohort. No differences in the level of activity were noted between hemizygotes and their respective wild-type controls. In contrast, homozygous Drd2-eGFP FVB/N animals had elevated activity. Only males were included in this study, except for the Swiss Webster group in which both male and female subjects were used. No significant differences were noted between male and female Swiss Webster mice, so the data from both were pooled. B, Activity measurements are plotted as distance traveled as a function of time. Note the elevated activity in the homozygous Drd2-eGFP FVB/N mice.