Differential targeting and function of α 2A and α 2C adrenergic receptor subtypes in cultured sympathetic neurons

Abstract

Previous research suggested that α 2A and α 2C adrenergic receptor (AR) subtypes have overlapping but unique physiological roles in neuronal signaling; however, the basis for these dissimilarities is not completely known. To better understand the observed functional differences between these autoreceptors, we investigated targeting and signaling of endogenously expressed α 2A and α 2CARs in cultured sympathetic ganglion neurons (SGN). At Days 1 and 4, α 2A and α 2CARs could be readily detected in SGN from wild-type mice. By Day 8, α 2AARs were targeted to cell body, as well as axonal and dendritic sites, whereas α 2CARs were primarily localized to an intracellular vesicular pool within the cell body and proximal dendritic projections. Expression of synaptic vesicle marker protein SV2 did not differ at Day 8 nor co-localize with either subtype. By Day 16, however, α 2CARs had relocated to somatodendritic and axonal sites and, unlike α 2AARs, co-localized with SV2 at synaptic contact sites. Consistent with a functional role for α 2ARs, we also observed that dexmedetomidine stimulation of cultured SGN more efficiently inhibited depolarization-induced calcium entry into older, compared to younger, cultures. These results provide direct evidence of distinct developmental patterns of endogenous α 2A and α 2CAR targeting and function in a native cell system and that maturation of SGN in culture leads to alterations in neuronal properties required for proper targeting. More importantly, the co-localization at Day 16 of α 2CARs at sites of synaptic contact may partially explain the differential modulation of neurotransmitter release and responsiveness to action potential frequency observed between α 2A and α 2CARs in SGN.