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Characterization of cAMP degradation by phosphodiesterases in the accessory olfactory system
1Department of Psychology, Boston University, 64 Cummington Street, Boston, MA 02215, USA. jcherry@bu.edu
Abstract:
To characterize the potential role of cAMP in pheromone transduction, we have examined the occurrence of cyclic nucleotide phosphodiesterases (PDEs) in the mouse vomeronasal organ (VNO). We show that the cAMP-specific isoforms PDE4A and PDE4D are found preferentially in the apical and basal layers, respectively, of the VNO neuroepithelium and in the rostral (PDE4A) and caudal (PDE4D) portions of the accessory olfactory bulb glomerular layer. Assays for cAMP hydrolysis showed that PDE activity in VNO homogenates was about half that measured in the cerebral cortex and olfactory epithelium, and the proportion of total activity inhibited by rolipram, a PDE4-specific inhibitor, was approximately 40%. Activity in the VNO was enhanced 60% by Ca(2+) and calmodulin (CaM), implicating the presence of Ca(2+)/CaM-dependent PDE1. Zaprinast, which is known to inhibit PDE1C isoforms, completely suppressed Ca(2+)/CaM-stimulated activity and, together, zaprinast and rolipram inhibited cAMP hydrolysis by approximately 70%. Our results suggest that PDE1 and PDE4 isoforms are the primary source of cAMP degradation in the VNO.
Insights
Cyclic nucleotide phosphodiesterases (PDEs) in the mouse vomeronasal organ (VNO) were investigated. PDE1 and PDE4 isoforms are the main enzymes responsible for cyclic adenosine monophosphate (cAMP) breakdown in the VNO.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- The vomeronasal organ (VNO) plays a crucial role in pheromone detection.
- Cyclic adenosine monophosphate (cAMP) is implicated in pheromone signal transduction pathways.
- Understanding the regulation of cAMP levels is essential for elucidating VNO function.
Purpose of the Study:
- To identify and characterize cyclic nucleotide phosphodiesterases (PDEs) in the mouse VNO.
- To determine the specific PDE isoforms involved in cAMP degradation within the VNO.
- To investigate the contribution of different PDE families to cAMP hydrolysis in the VNO.
Main Methods:
- Immunohistochemical localization of PDE isoforms (PDE4A, PDE4D) in VNO neuroepithelium and accessory olfactory bulb.
- Enzymatic assays measuring cAMP hydrolysis in VNO homogenates.
- Inhibition studies using rolipram (PDE4-specific inhibitor) and zaprinast (PDE1C inhibitor).
- Assessment of Ca(2+)/calmodulin (CaM) stimulation of PDE activity.
Main Results:
- PDE4A and PDE4D isoforms were localized to specific layers and regions of the VNO and accessory olfactory bulb.
- VNO homogenates exhibited significant cAMP hydrolysis activity, partially inhibited by rolipram.
- Ca(2+)/CaM stimulation indicated the presence and activity of PDE1.
- Combined inhibition by rolipram and zaprinast demonstrated that PDE1 and PDE4 isoforms account for approximately 70% of cAMP hydrolysis.
Conclusions:
- PDE1 and PDE4 isoforms are the primary enzymes responsible for cAMP degradation in the mouse VNO.
- These findings provide insights into the regulation of cAMP signaling in pheromone transduction.
- The localization of PDE isoforms suggests specific roles in different VNO compartments.