Caged Zn²⁺ Photolysis in Zebrafish Whole Brains Reveals Subsecond Modulation of Dopamine Uptake

Free, ionic zinc (Zn²⁺) modulates neurotransmitter dynamics in the brain. However, the sub-s effects of transient concentration changes of Zn²⁺ on neurotransmitter release and uptake are not well understood. To address this lack of knowledge, we have combined the photolysis of the novel caged Zn²⁺ compound [Zn(DPAdeCageOMe)]⁺ with fast scan cyclic voltammetry (FSCV) at carbon fiber microelectrodes in live, whole brain preparations from zebrafish (Danio rerio). After treating the brain with [Zn(DPAdeCageOMe)]⁺, Zn²⁺ was released by application of light that was gated through a computer-controlled shutter synchronized with the FSCV measurements and delivered through a 1 mm fiber optic cable. We systematically optimized the photocage concentration and light application parameters, including the total duration and light-to-electrical stimulation delay time. While sub-s Zn²⁺ application with this method inhibited DA reuptake, assessed by the first-order rate constant (k) and half-life (t_1/2), it had no effect on the electrically stimulated DA overflow ([DA]_STIM). Increasing the photocage concentration and light duration progressively inhibited uptake, with maximal effects occurring at 100 μM and 800 ms, respectively. Furthermore, uptake was inhibited 200 ms after Zn²⁺ photorelease, but no measurable effect occurred after 800 ms. We expect that application of this method to the zebrafish whole brain and other preparations will help expand the current knowledge of how Zn²⁺ affects neurotransmitter release/uptake in select neurological disease states.