These transgenic mice express spH, the pH-sensitive variant of the enhanced green fluorescent protein (ecliptic 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 spH64, transgene expression is detected in many regions of the brain. spH expression is detected mainly in GABAergic or inhibitory synaptic terminals of dissociated hippocampal neurons. Synaptic activity, as determined by fluorescence, is detectable starting at approximately 10 days in vitro in cultured hippocampal neurons. The Jackson Laboratory 2024, used with permission.