Two-photon laser scanning microscopic (TPLSM) images of FM1-43 vesicular release from Mossy fiber terminals in field CA3 of hippocampal slices confirm that release probability is reduced by chronic Pb²⁺ exposure.

(A) Representative TPLSM pseudocolor images of FM1-43 loaded presynaptic terminals in proximal stratum radiatum of field CA3c in hippocampal slices from Pb²⁺-treated (Lead) and Control rats imaged prior to (0 min) and after 10 minutes (10 min) of 2Hz Mossy fiber stimulation (Calibration Bar: 5 μm). (B) Time course (Mean ± SEM) of stimulus-evoked FM1-43 destaining from large Mossy fiber puncta in field CA3 of hippocampal slices in response to 2Hz Schaffer collateral stimulation (solid bar) in control (solid circles, N = 5 slices, 25 puncta) versus chronically Pb²⁺-treated (open circles, N = 6 slices, 27 puncta) rats. Overall, decay time constants were not statistically significantly smaller in slices from Pb²⁺-treated rats (white bars) compared to those from control rats (black bars). However, a significant effect of Pb²⁺ was observed at the later time points in the 2Hz train (gray bar; * P < 0.05, Student’s t-test comparing open and black squares).