Activation of group I mGluRs increases transmitter release. ai, A paired recording from a presynaptic giant axon and a postsynaptic ventral horn neuron. Top, Intracellular recording from a reticulospinal axon with five action potentials evoked every 25 msec. Bottom, EPSCs evoked by the presynaptic action potentials above. The black traceshows the control response; the graytrace shows the response in CPCCOEt (100 μm). aii, Histogram showing the pooled data of the EPSC amplitude reduction by CPCCOEt (n= 3) from paired recordings (as in ai) for each EPSC in the train. Asterisks show where the reduction is significantly different from controls (p < 0.05). bi, Integrated Ca²⁺ imaging data taken from a reticulospinal axon. The response is to five stimuli (arrowheads) at 50 Hz applied to the axon. Data are shown before (black) and after (gray) the addition of CPCCOEt (100 μm) and after washing the drug from the superfusate (black). bii, Data taken from the same axon as in bi, with a single stimulus (arrowhead). Data are shown before (black) and after (gray) application of CPCCOEt (100 μm) and the washout (black).