Cross-pathway integration of cAMP signals through cGMP and calcium-regulated phosphodiesterases in mouse striatal cholinergic interneurons

Abstract

Acetylcholine plays a key role in striatal function, yet the intricate dynamics of cyclic nucleotide signaling which govern the firing properties of cholinergic interneurons (ChINs) have remained elusive. Since phosphodiesterases determine the dynamics of cyclic nucleotides, in this study, we used FRET biosensors and pharmacological compounds to examine phosphodiesterase activity in ChINs in mouse brain slices. Intriguingly, these neurons displayed strikingly low levels and slow cAMP responsiveness compared to medium-sized spiny neurons (MSNs). Our experiments revealed that PDE1, PDE3 and PDE4 are important regulators of cAMP level in ChINs. Notably, the induction of cGMP production by nitric oxide (NO) donors increases cAMP by inhibiting PDE3 - a mechanism hitherto unexplored in neuronal context. Furthermore, the activation of NMDA or metabotropic glutamate receptors increases intracellular calcium, consequently activating PDE1 and thereby decreasing both cAMP and cGMP. This interplay of phosphodiesterases enables the control of cAMP by the neuromodulatory influences of glutamate and NO. Remarkably, the NO/cGMP signal results in different effects: NO enhances cAMP in ChINs by inhibiting PDE3, whereas it reduces cAMP levels in MSNs by activating PDE2A. These findings underscore the specificity of intracellular signaling in ChINs compared to MSNs and show how the NO-cGMP pathway affects these various neuronal types differently. These observations have significant implications for understanding the regulation of the striatal network and the integration of dopaminergic signals and suggest innovative therapeutic strategies for addressing basal ganglia disorders with unmet medical need.