Abstract
Background:
5-Hydroxytryptamine (5HT) modulates
N
-methyl-
d
-aspartate (NMDA) depolarization.
Results:
5HT2C co-immunoprecipitates with GluN2A and enhances NMDA motoneuronal depolarization through phosphorylation of Src
Tyr-416
.
Conclusion:
5HT modulates NMDA through Src phosphorylation in a molecular complex that is localized in the processes of spinal neurons.
Significance:
5HT2C modulation of NMDA excitation is coordinated by a molecular complex.
N
-Methyl-
d
-aspartate (NMDA)-gated ion channels are known to play a critical role in motoneuron depolarization, but the molecular mechanisms modulating NMDA activation in the spinal cord are not well understood. This study demonstrates that activated 5HT2C receptors enhance NMDA depolarizations recorded electrophysiologically from motoneurons. Pharmacological studies indicate involvement of Src tyrosine kinase mediates 5HT2C facilitation of NMDA. RT-PCR analysis revealed edited forms of 5HT2C were present in mammalian spinal cord, indicating the availability of G-protein-independent isoforms. Spinal cord neurons treated with the 5HT2C agonist MK 212 showed increased Src
Tyr-416
phosphorylation in a dose-dependent manner thus verifying that Src is activated after treatment. In addition, 5HT2C antagonists and tyrosine kinase inhibitors blocked 5HT2C-mediated Src
Tyr-416
phosphorylation and also enhanced NMDA-induced motoneuron depolarization. Co-immunoprecipitation of synaptosomal fractions showed that GluN2A, 5HT2C receptors, and Src tyrosine kinase form protein associations in synaptosomes. Moreover, immunohistochemical analysis demonstrated GluN2A and 5HT2C receptors co-localize on the processes of spinal neurons. These findings reveal that a distinct multiprotein complex links 5-hydroxytryptamine-activated intracellular signaling events with NMDA-mediated functional activity.
