Neferine, a bisbenzylisoquinoline alkaloid of Nelumbo nucifera, inhibits glutamate release in rat cerebrocortical nerve terminals through 5-HT _1A receptors

Neferine, a bisbenzylisoquinoline alkaloid present in Nelumbo nucifera, has been reported to exhibit neuroprotective effects. Because reduced glutamatergic transmission through inhibition of glutamate release has been proposed as a mechanism of neuroprotection, we investigated whether and how neferine inhibits glutamate release in the nerve terminals of the cerebral cortex of rats. The results demonstrated that neferine inhibits the glutamate release that is evoked by the potassium channel blocker 4-aminopyridine, doing so in a dose-dependent manner. This effect was prevented by removing extracellular calcium and blocking vesicular transporters or N- and P/Q-type calcium channels but not by blocking glutamate transporters. Neferine decreased the 4-aminopyridine-stimulated elevation in intrasynaptosomal calcium concentration; however, it had no effect on the synaptosomal membrane potential. The inhibition of glutamate release by neferine was also eliminated by the selective 5-hydroxytryptamine 1A (5HT_1A) receptor antagonist WAY100635, Gi/o protein inhibitor pertussis toxin, adenylyl cyclase inhibitor MDL12330A, and protein kinase A inhibitor H89. Moreover, immunocytochemical analysis revealed the presence of 5-HT_1A receptor proteins in the vesicular transporter of glutamate type 1 positive synaptosomes. The molecular docking study also demonstrated that neferine exhibited the highest binding affinity with 5-HT_1A receptors (Autodock scores for 5-HA_1A = -11.4 kcal/mol). Collectively, these results suggested that neferine activates 5-HT_1A receptors in cortical synaptosomes, which decreases calcium influx and glutamate release through the activation of Gi/o protein and the inhibition of adenylyl cyclase/cAMP/protein kinase A cascade.

Keywords: 5-HT(1A) receptor; Cerebrocortical nerve terminals; Glutamate release; Neferine; Protein kinase a; Voltage-dependent Ca(2+) channels.