I am reading the paper: Pyramidal Cell-Interneuron Interactions Underlie Hippocampal Ripple Oscillations. The authors use CAG::ChR2 rats (for example in Figure 2) and I don't know what it means. I understand for example that in PV::ChR2 mice, parvalbumin neurons will be activated by light. I am also familiar with types of other interneurons (Ivy, Martinotti, OLM, LTS, Bistratified, Mopp, VIP, Somatostatin...) but I have never encountered CAG cells.
Is CAG represent a type of neuron? or, maybe it represents something else?