Activation of α7 nicotinic acetylcholine receptors increases intracellular cAMP levels via activation of AC1 in hippocampal neurons

The activation of alpha 7 nAChRs has been shown to improve hippocampal-dependent learning and memory. However, the molecular mechanism of alpha 7 nAChRs' action remains elusive. We previously reported that activation of alpha 7 nAChRs induced a prolonged enhancement of glutamatergic synaptic transmission in a PICA-dependent manner. Here, we investigated any connection between the activation of the alpha 7 nAChR and cAMP signaling in hippocampal neurons. To address this question, we employed a FRET-based biosensor to measure the intracellular cAMP levels directly via live cell imaging. We found that application of the alpha 7 nAChR-selective agonist choline, in the presence of the alpha 7 nAChR positive allosteric modulator PNU-120596, induced a significant change in emission ratio of F535/F470, which indicated an increase in intracellular cAMP levels. This choline-induced increase was abolished by the alpha 7 nAChR antagonist MLA and the calcium chelator BAPTA, suggesting that the cAMP increase depends on the alpha 7 nAChR activation and subsequent intracellular calcium rise. The selective AC1 inhibitor CB-6673567 and siRNA-mediated deletion of AC1 both blocked the choline-induced cAMP increase, suggesting that calcium-dependent AC1 is required for choline's action. Furthermore, alpha 7 nAChR activation stimulated the phosphorylation of synapsin, which serves as a downstream effector to regulate neurotransmitter release. Our findings provide the first direct evidence to link activation of alpha 7 nAChRs to a cAMP rise via AC1, which defines a new signaling pathway employed by alpha 7 nAChRs. Our study sheds light into potential molecular mechanisms of the positive cognitive actions of alpha 7 nAChR agonists and development of therapeutic treatments for cognitive impairments. Published by Elsevier Ltd.