Sparse Cre-Expressing Cortical Neurons

This study was carried out in accordance with the recommendations of UK Animals (Scientific Procedures) Act 1986 under Home Office Project and Personal Licenses (project licenses 70/7818 and 70/9095). The protocol was approved by the UK Home Office. Transgenic mice were bred to express VSFP Butterfly 1.2 in cortical layer 2/3 pyramidal neurons under the intersectional control of TetO and Cre-recombinase [Figure 2B, “sparse PC line,” Rasgrf2-dCre; CaMK2A-tTA; Ai78 (Mayford et al., 1996 (link); Harris et al., 2014 (link); Madisen et al., 2015 (link))]. To induce sparse expression through stochastic re-stabilization of destabilized Cre, a titrated total dose of 2E-4 mg/kg Trimethoprim (TMP, Sigma) was given via multiple intra-peritoneal injections over 2 consecutive days as described in Song et al. (2017 (link)). For comparison, transgenic mice densely expressing chimeric VSFP-Butterfly in all pyramidal cells were used [“pan PC line,” CaMK2A-tTA; tetO-chiVSFP (Song et al., 2018 (link))].