Figure 8. Paired pulse modulation in physiological conditions.

A, in 1.8 mm extracellular calcium, the modulation of the GC-to-MC synapse is unchanged from that measured at 2.5 mm calcium, exhibiting marked paired-pulse depression at all intervals examined (□). The data could be described by a nearly flat line (or a single exponential with a very long time constant). At three interstimulus intervals (25, 100 and 1000 ms), the level of depression is unchanged at 1.8 mm calcium and 35°C (▪). At all intervals and temperatures, the level of depression is not statistically significantly different from levels measured in 2.5 mm calcium. B, in 1.8 mm calcium (○), the modulation of the MC-to-GC synapse shows a combination of depression and facilitation unchanged from that measured at 2.5 mm calcium, and the effect is unaltered at 35°C (•). The fitted line is a sum of two exponentials – one for depression has a time constant of 35 ms and one for facilitation 100 ms. For GC-to-MC synapses, n = 6 at room temperature and 6 at 35°C, and for MC-to-GC synapses, n = 13 at room temperature and 10–16 at 35°C.