Modification of hippocampal excitability in brain slices pretreated with a low nanomolar concentration of Zn2+

Synaptic Zn²⁺ homeostasis may be changed during brain slice preparation. However, much less attention has been paid to Zn²⁺ in artificial cerebrospinal fluid (ACSF) used for slice experiments than has been paid to Ca²⁺. The present study assesses addition of Zn²⁺ to ACSF, focused on hippocampal excitability after acute brain slice preparation. When the static levels of intracellular Zn²⁺ and Ca²⁺ were compared between brain slices prepared with conventional ACSF without Zn²⁺ and those pretreated with ACSF containing 20 nM ZnCl₂ for 1 hr, both levels were almost the same. On the other hand, intracellular Ca²⁺ levels were significantly increased in the stratum lucidum of the control brain slices after stimulation with high K⁺, although the increase was significantly suppressed by the pretreatment with ACSF containing Zn²⁺, suggesting that neuronal excitation is enhanced in brain slices prepared with ACSF without Zn²⁺. The increase in extracellular Zn²⁺ level, an index of glutamate release, after stimulation with high K⁺ was also significantly suppressed by pretreatment with ACSF containing Zn²⁺. When mossy fiber excitation was assessed in brain slices with FM4‐64, an indicator of presynaptic activity, attenuation of FM 4‐64 fluorescence based on presynaptic activity was suppressed in the stratum lucidum of brain slices pretreated with ACSF containing Zn²⁺. The present study indicates that hippocampal excitability is enhanced in brain slices prepared with ACSF without Zn²⁺. It is likely that a low nanomolar concentration of Zn²⁺ is necessary for ACSF. © 2015 Wiley Periodicals, Inc.