Inhibitory zinc-enriched terminals in the mouse cerebellum: double-immunohistochemistry for zinc transporter 3 and glutamate decarboxylase

In the present study, we showed for the first time the presence of inhibitory zinc-enriched neuron terminals in the mouse cerebellar cortex by means of double-immunohistochemistry for zinc transporter 3 (ZnT3) and glutamate decarboxylase (GAD). The co-localization of ZnT3 and GAD in the cerebellar cortex was analyzed by confocal microscopy. Strong, punctuate ZnT3-immunoreactivity (Ir) was predominantly distributed in the granule cell layer, while GAD-Ir was seen throughout the cerebellar cortical layers. All of the ZnT3-immunoreactive structures were also immunopositive to GAD, but not vice versa. Based on size and position, these double-labeled elements were axonal terminals of the Golgi and basket cells, in the granule cell and molecular layers, respectively. Observations by electron microscopy revealed that ZnT3-immunoreactive terminals showed typical characteristics of the inhibitory synapses like the following: (1) presynaptic terminals containing flat vesicles; and (2) symmetrical synaptic contacts with dendritic elements. The present results indicate that a zinc-containing GABAergic system exists in the mouse cerebellar cortex.