Modification of hippocampal excitability in brain slices pretreated with a low nanomolar concentration of Zn super(2+)

Synaptic Zn super(2+) homeostasis may be changed during brain slice preparation. However, much less attention has been paid to Zn super(2+) in artificial cerebrospinal fluid (ACSF) used for slice experiments than has been paid to Ca super(2+). The present study assesses addition of Zn super(2+) to ACSF, focused on hippocampal excitability after acute brain slice preparation. When the static levels of intracellular Zn super(2+) and Ca super(2+) were compared between brain slices prepared with conventional ACSF without Zn super(2+) and those pretreated with ACSF containing 20 nM ZnCl sub(2) for 1 hr, both levels were almost the same. On the other hand, intracellular Ca super(2+) levels were significantly increased in the stratum lucidum of the control brain slices after stimulation with high K super(+), although the increase was significantly suppressed by the pretreatment with ACSF containing Zn super(2+), suggesting that neuronal excitation is enhanced in brain slices prepared with ACSF without Zn super(2+). The increase in extracellular Zn super(2+) level, an index of glutamate release, after stimulation with high K super(+) was also significantly suppressed by pretreatment with ACSF containing Zn super(2+). 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 Zn super(2+). The present study indicates that hippocampal excitability is enhanced in brain slices prepared with ACSF without Zn super(2+). It is likely that a low nanomolar concentration of Zn super(2+) is necessary for ACSF. Hippocampal excitability is more enhanced in brain slices prepared with conventional artificial cerebrospinal fluid (ACSF) without Zn super(2+) than in those pretreated with ACSF containing 20 nM ZnCl sub(2) for 1 hr. It is likely that a low nanomolar concentration of Zn super(2+) is necessary for ACSF.