Some glutamatergic synapses in the mammalian central nervous system ex
hibit high levels of free ionic zinc in their synaptic vesicles. The p
recise role of this vesicular zinc remains obscure: despite suggestive
evidence for zinc as a neuromodulator. As a step towards elucidating
the role of free zinc in the brain we have developed a method for imag
ing zinc release in live brain slices. A newly synthesized zinc-sensit
ive fluorescent probe, N-(6-methoxy-8-quinolyl)-p-carboxybenzo sulphon
amide (TFLZn), was used to monitor intracellular zinc in live rat hipp
ocampal slices. The dye loaded into the zinc-rich synaptic vesicles of
the messy fibre terminals in the hippecampal formation. Direct electr
ical stimulation of the messy fibre pathway diminished the fluorescenc
e in the messy fibre terminals, consistent with a stimulus-dependent z
inc release. The synaptic release of zinc was followed by the rapid re
plenishment of the zinc levels in vesicles from an as yet unidentified
intracellular zinc source. Furthermore, we present evidence that zinc
may play a role in a form of long-term potentiation exhibited by the
messy fibre pathway. (C) 1997 IBRO. Published by Elsevier Science Ltd.