A model of zinc dynamics evoked by intense stimulation at the cleft of hippocampal mossy fiber synapses

Zinc is a transition metal that is particularly abundant in the mossy fibers of the hippocampal CA3 area. Despite the large number of studies about the zinc role in mossy fibers, the action of zinc in synaptic mechanisms is only partly known. The use of computational models can be a useful tool for this study. In a previous work, a model was developed to evaluate zinc dynamics at the mossy fiber synaptic cleft, following weak stimulation, insuf-ficient to evoke zinc entry into postsynaptic neurons. For intense stimulation, cleft zinc effluxes must be considered. Therefore, the initial model was extended to include postsynaptic zinc effluxes based on the Goldman-Hodgkin-Katz current equation combined with Hodgkin and Huxley conductance changes. These ef-fluxes occur through different postsynaptic escape routes, namely L-and N-types voltage-dependent calcium channels and NMDA receptors. For that purpose, various stimulations were assumed to induce high concen-trations of cleft free zinc, named as intense (10 mu M), very intense (100 mu M) and extreme (500 mu M). It was observed that the main postsynaptic escape routes of cleft zinc are the L-type calcium channels, followed by the NMDA receptor channels and by N-type calcium channels. However, their relative contribution for cleft zinc clearance was relatively small and decreased for higher amounts of zinc, most likely due to the blockade action of zinc in postsynaptic receptors and channels. Therefore, it can be concluded that the larger the zinc release, the more predominant the zinc uptake process will be in the cleft zinc clearance.

Automated summary

Zinc is abundant in the mossy fibers of the hippocampal CA3 area and its role in synaptic mechanisms is still not fully understood. Computational models have been used to study the dynamics of zinc at the mossy fiber synaptic cleft. The models were extended to include postsynaptic zinc effluxes and the results showed that the main escape routes for cleft zinc are L-type calcium channels, NMDA receptor channels, and N-type calcium channels.