Figure 6. An increase of the ratio of extracellular Ca²⁺ and Mg²⁺ concentration promotes the development of synaptic resistance to depotentiation stimulation.

A, summary of experiments showing that bath application of SCH50911 (20 μm) caused a significant increase in the amplitude of mossy fibre fEPSPs (n = 5). B, summary of experiments showing that an increase in the extracellular Ca²⁺/Mg²⁺ concentration ratio from 4 mm/4 mm to 4 mm/2 mm mimicked the effect of SCH50911 on baseline mossy fibre transmission (n = 10). C, summary of experiments showing that in 4 mm Ca²⁺ and 2 mm Mg²⁺ aCSF, application of LFS at 10 min after two trains of 100 Hz HFS initially depressed fEPSPs that subsequently recovered to previously potentiated level (n = 5; •). Field EPSPs in slices that received HFS without LFS exhibited persistent potentiation (n = 5; ○).