Abstract
The synaptic transmission is potentiated by the activation of adenylyl cyclase (AC) and protein kinase A (PKA) at hippocampal mossy fiber-CA3 synapses. Although the AC/PKA activation was suggested to facilitate the transmitter release from MF presynaptic terminals, the most of these classical evidences were indirect. In this study the presynaptic exocytosis was directly investigated in the hippocampal slice of a synaptopHluorin (SpH) transgenic mouse (TV-42 line) which expresses SpH specifically at the mossy fiber terminals of hippocampus (Araki et al. 2005). The repetitive stimulation (10 Hz for 1 s) of mossy fiber bundle transiently increased the SpH fluorescence in the presynaptic terminal. The SpH fluorescence was sampled before and after application of forskolin (50 μM) and IBMX (100 μM), a combination which activates AC/PKA. The AC/PKA activation increased the activity-dependent increment of SpH (ΔSpH) by 2.42 ± 0.49 (mean ± SEM, n = 29) on average (p<0.001). However, both the rising and falling time course of ΔSpH was not changed. The ΔSpH was also largely facilitated in the presynaptic terminal of which it was null at baseline. It is suggested that the AC/PKA activation facilitates the presynaptic exocytosis and that it turns some presynaptically silent synapses into active. Ref: Araki R. et al. (2005) genesis 42, 53-60. [J Physiol Sci. 2006;56 Suppl:S20]
