Presynaptic enhancement of excitatory synaptic transmission by β- adrenergic receptor activation

1. Previous studies have shown that β-adrenergic receptor activation has many effects on neuronal function in hippocampal area CA1. However, all of the physiological effects of β-adrenergic receptor activation in this region reported to date have been attributed to postsynaptic mechanisms. A series of studies was performed to test the hypothesis that β-adrenergic receptor activation also acts presynaptically to enhance excitatory synaptic transmission. 2. Application of the selective β-adrenergic agonist isoproterenol to hippocampal slices induced an increase in the amplitude of evoked excitatory postsynaptic currents (EPSCs) in CA1 pyramidal cells. This response was potentiated in the presence of a cyclic nucleotide phosphodiesterase inhibitor. Isoproterenol also resulted in the appearance of a late inward synaptic current that likely represents polysynaptically evoked EPSCs. Both the increased amplitude of the monosynaptic EPSC and the appearance of polysynaptic EPSCs in response to isoproterenol were blocked by H89, an inhibitor of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase. 3. Isoproterenol induced an increase in the frequency of spontaneous miniature EPSCs but did not affect the amplitude of these currents. In addition, isoproterenol had no effect on currents elicited by direct application of the ionotropic glutamate receptor agonist, (R,S)-α- amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). 4. These results suggest that activation of presynaptic β-adrenergic receptors enhances synaptic transmission in area CA1 via activation of cAMP-dependent protein kinase.