• Angélica Almanza, Pedro Segura-Chama, Martha León-Olea, Enoch Luis, René Garduño-Gutiérrez, Jonathan Mercado-Reyes, Karina Simón-Arceo, Ulises Coffeen, Arturo Hernández-Cruz, Francisco Pellicer, and Francisco Mercado.
• Laboratorio de Fisiología Celular, Dirección de Investigaciones en Neurociencias, Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz, Ciudad de México, Mexico.
• Neuroscience. 2019 Oct 1; 417: 81-94.

AbstractIntrathecal (i.t.) administration of quinpirole, a dopamine (DA) D2-like receptor agonist, produces antinociception to mechanonociceptive stimuli but not to thermonociceptive stimuli. To determine a cellular mechanism for the specific antinociceptive effect of D2-like receptor activation on mechanonociception, we evaluated the effect of quinpirole on voltage-gated Ca2+ influx in cultured dorsal root ganglion (DRG) neurons and the D2 DA receptor distribution in subpopulations of rat nociceptive DRG neurons. Small-diameter DRG neurons were classified into IB4+ (nonpeptidergic) and IB4- (peptidergic). Intracellular [Ca2+] microfluorometry and voltage-clamp experiments showed that quinpirole reduced Ca2+ influx and inhibited the high voltage-activated Ca2+ current (HVA-ICa) in half of IB4+ neurons, leaving Ca2+ entry and HVA-ICa in IB4- neurons nearly unaffected. Pretreatment with ω-conotoxin MVIIA prevented the effect of quinpirole on HVA-ICa from IB4+ neurons, indicating that quinpirole mainly inhibits CaV2.2 channels. Immunofluorescence experiments showed that D2 DA receptor was present mainly in IB4+ small DRG neurons. Finally, in behavioral experiments in rats, the clinically approved D2-like receptor agonist pramipexole produced spinal antinociception in a similar fashion to quinpirole, with a significant effect only in the mechanonociceptive test. Our results explain, at least in part, why D2-like receptor agonists produce antinociception on mechanonociceptors.Copyright © 2019 IBRO. Published by Elsevier Ltd. All rights reserved.

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