fEPSPs represent action potentials within a population of neurons. However, we previously showed that CIE and WD can increase presynaptic function at local BLA glutamatergic synapses (Lack et al., 2007). To examine whether similar effects might be responsible for increased synaptic responsiveness at EC-BLA synapses, we carried out a paired pulse facilitation experiment to measure presynaptic release probability indirectly with postsynaptic responses to pairs of electrical stimuli. We used inter-pulse intervals of 25, 50 and 250msec to determine the ratio of the second synaptic response to the first across times that yield information about release probability (25 and 50msec; (Andreasen and Hablitz, 1994; Katz et al., 1993)) as well as autoreceptor-mediated decreases in presynaptic function (250msec; (Brucato et al., 1992)). We compared the ratios of the CIE and WD treated slices to those of control slices. We found no significant difference (one-way ANOVA) between paired pulse ratios in the CIE (n=10) or 24WD (n=10) neurons compared to CON (n=10) at any of the intervals tested (Fig. 4 A & B). This suggests that the increased response at EC to BLA synapses seen in CIE and WD with the fEPSP measures does not involve a significant change in presynaptic release probability.
