Figure 4.

Lowering P_r at stronger synapses does not unmask response to BDNF. (A) Example for absence of BDNF effect after lowering P_r by reducing [Ca²⁺]_o. Initial EPSC was ∼−1050 pA and was reduced to −30 pA after reducing [Ca²⁺]_o from 3 to 0.5 mm and elevating [Mg²⁺]_o from 2 to 3 mm. The vertical line depicts the time point following lowering [Ca²⁺]_o, after which EPSCs amplitudes were normalized to the new mean value recorded during the last 10 min prior to exposure to BDNF (100 ng/ml). Shown at top are sample traces of EPSCs (average of 10 events). Scales, 200 pA, 10 msec (left two traces), and 10 pA, 10 msec (right three traces). Duration of low [Ca²⁺]_o and BDNF treatments are indicated by the thick lines below. (*) Monosynaptic EPSCs monitored. Note that polysynaptic currents disappeared after the low [Ca²⁺]_o treatment. (B) Summary of results from experiments in which P_r was reduced by either treatment with low [Ca²⁺]_o or with adenosine. Potentiation factor observed after the BDNF treatment was defined as in Fig. 3. Bars represent average values obtained from all experiments on weak synapses (EPSC amplitude <600 pA) and strong synapses (>800 pA) in the normal recording medium as well as experiments on strong synapses (>800 pA) in the presence of low [Ca²⁺]_o and adenosine. The average EPSC amplitude before and after the low [Ca²⁺]_o or adenosine treatment is shown at bottom. (N.A.), Not applicable. Error bars, s.e.m.