Fig. 2. PTP at the SN–MN is not uniform, and only initially weak synapses are sensitive to postsynaptic BAPTA injection.A, The magnitude of PTP induced at the SN–MN synapse is inversely proportional to the initial size of the synapse (white bars), with the weakest synapses showing the greatest amount of PTP. Injections of BAPTA into the MN significantly reduced PTP at the weaker synapses but did not affect the amount of PTP induced at the stronger synapses (compare black bars with white bars). For control groups, 1–3 mV (n = 7), 3–5 mV (n = 5), 5–7 mV (n = 5), 7–9 mV (n = 4), and 10+ mV (n = 7); for BAPTA groups, 1–3 mV (n = 8), 3–5 mV (n = 7), 5–7 mV (n = 4), 7–9 mV (n = 6), and 10+ (n = 5).B1
, Representative SN–MN traces in which both synapses were initially weak. The magnitude of PTP at the BAPTA-loaded synapse was only half of the amount seen at the control synapse. B2
, Representative SN–MN traces in which both synapses were initially strong. There was no difference in the magnitude of PTP induced at the BAPTA-loaded and control synapse.