Phosphodiesterase 1C is dispensable for rapid response termination of olfactory sensory neurons

Abstract

Phosphodiesterase (PDE) activity in olfactory sensory neuron cilia is thought to be responsible for degrading odor-induced signaling, resulting in rapid response termination. However, disrupting the variety of PDE found only in cilia unexpectedly turns out not to result in a rapid response termination deficit. Only eliminating both cilia-localized and cell body–localized varieties of PDEs resulted in prolonged termination. In the nose, odorants are detected on the cilia of olfactory sensory neurons (OSNs), where a cAMP-mediated signaling pathway transforms odor stimulation into electrical responses. Phosphodiesterase (PDE) activity in OSN cilia has long been thought to account for rapid response termination by degrading odor-induced cAMP. Two PDEs with distinct cellular localization have been found in OSNs: PDE1C in the cilia and PDE4A throughout the cell but absent from the cilia. We disrupted both of these genes in mice and carried out electro-olfactogram analysis. Unexpectedly, eliminating PDE1C did not prolong response termination. Prolonged termination occurred only in mice that lacked both PDEs, suggesting that cAMP degradation by PDE1C in cilia is not a rate-limiting factor for response termination in wild-type mice. Pde1c−/− OSNs instead showed reduced sensitivity and attenuated adaptation to repeated stimulation, suggesting that PDE1C may be involved in regulating sensitivity and adaptation. Our observations provide new perspectives on the regulation of olfactory transduction.