These transgenic mice express spH, the pH-sensitive variant of the green fluorescent protein (superecliptic pHluorin) fused to the mouse synaptic vesicle-associated membrane protein 2 (Vamp2), under the control of the mouse thymus cell antigen 1 (Thy1) promoter. In founder line spH21, transgene expression is detected in glutamatergic or excitatory neurons of many brain regions, including the cortex and the hippocampus. Synaptic activity, as determined by fluorescence, is detectable starting at approximately 14 days in vitro in cultured hippocampal neurons. The Jackson Laboratory 2024, used with permission.