IMAGING FREE ZINC IN SYNAPTIC TERMINALS IN LIVE HIPPOCAMPAL SLICES

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.