Measurement of presynaptic zinc changes in hippocampal mossy fibers.

The hippocampal mossy fiber terminals of CA3 area contain high levels of vesicular zinc that is released in a calcium-dependent way, following high-frequency stimulation. However the properties of zinc release during normal synaptic transmission, paired-pulse facilitation and mossy fiber long-term potentiation are still unknown. Using the fluorescent zinc probe N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide, we measured fast mossy fiber zinc changes indicating that zinc is released following single and low levels of electrical stimulation. The observed presynaptic zinc signals are maintained during the expression of mossy fiber long-term potentiation, assumed to be mediated by an increase in transmitter release, and are enhanced during paired-pulse facilitation. This zinc enhancement is, like paired-pulse facilitation, reduced during established long-term potentiation. The correlation between the paired-pulse evoked zinc and field potential responses supports the idea that zinc is co-released with glutamate.