This image shows a coronal section of an olfactory bulb from a GAD1-GFP^+/−::vGluT1- Cre^+/−::LSL-H2B mCherry^+/− mouse that was generated to perform whole-brain analysis of glutamate-to-GABA neurotransmitter switching. Red dots indicate the nuclei of glutamatergic neurons, while the green GFP signal fills the cell bodies of neurons expressing GABA at the time of the experiments. Cells co-expressing GABA and glutamate will therefore be mCherry⁺ and GFP⁺. While mCherry⁺/GFP⁺ neurons are also present under normal conditions, their number will increase when neurotransmitter switching occurs. For more information, see the Viewpoints article by Li et al. (pages 4078–4089).