Fig. 6.

Unlike in control cultures, paired-pulse facilitation (PPF) occurs in both control and 10 mmCa²⁺/0.5 mm Mg²⁺containing saline after BoNT/A or BoNT/C treatment. A, Dual recordings of monosynaptically connected CA3 pyramidal neurons recorded in a control (left) and a BoNT/A-treated culture (right). Top traces are pairs of presynaptic action potentials with an interval of 50 msec.Bottom traces are representative single sweeps of postsynaptic unitary currents elicited either in control saline containing 2.8 mm Ca²⁺/2.5 mm Mg²⁺ or in saline containing 10 mm Ca²⁺/0.5 mmMg²⁺. In the control cell pair, application of 10 mm Ca²⁺/0.5 mmMg²⁺ produced an increase in release probability, and paired-pulse depression was observed in 97% of the individual trials. In contrast, in the cell pair from a BoNT/A-treated culture, PPF was observed in 64% of the individual trials in the presence of 10 mm Ca²⁺/0.5 mmMg²⁺ containing saline, and failures of EPSC1 occurred in 93% of trials in control saline. B, In control cultures the mean paired-pulse ratio between two CA3 pyramidal cells was >1 in control saline but <1 after the release probability was increased by raising the Ca²⁺/Mg²⁺ ratio. In BoNT/A- and BoNT/C-treated cultures, the paired-pulse ratio was >1 in saline containing 10 mm Ca²⁺/0.5 mmMg²⁺. Failures of transmission were included in the calculation of the paired-pulse ratio.