Bay k 8644

During the opioid epidemic there has been a significant increase in the number of prescriptions for gabapentinoids (gabapentin and pregabalin), which block the α₂δ-subunit of voltage-gated calcium channels (VGCCs). In rats, gabapentinoids enhance the potency of the mu opioid receptor (MOR) agonists fentanyl and heroin and decrease the potency of the stimulant drugs cocaine and d-methamphetamine to elicit discriminative stimulus effects. Moreover, (±)-BAY-K-8644, a dihydropyridine-type agonist at the α₁-subunit of VGCCs (α₁-VGCCs), prevents the antiallodynic effects of gabapentin in rats. The mechanism(s) of interaction between gabapentinoids and MOR agonists and between gabapentinoids and stimulant drugs is/are unclear. This study tested the following hypotheses: (1) the dihydropyridine-type α₁-VGCC blocker nimodipine increases the potency of MOR agonists to elicit discriminative stimulus effects; and (2) (±)-BAY-K-8644 attenuates the ability of gabapentinoids and nimodipine to increase the potency of MOR agonists to elicit discriminative stimulus effects. In rats trained to discriminate fentanyl (0.0032 mg/kg) or cocaine (3.2 mg/kg) from saline, neither (±)-BAY-K-8644 nor nimodipine elicited significant fentanyl- or cocaine-appropriate responding. (±)-BAY-K-8644 did not significantly alter discrimination dose-effect functions of MOR agonists or stimulant drugs whereas nimodipine dose-dependently shifted the MOR agonist discrimination dose-effect functions to the left and the stimulant drug discrimination dose-effect functions to the right. (±)-BAY-K-8644 dose-dependently attenuated the ability of nimodipine and gabapentinoids to increase the potency of MOR agonists and decrease the potency of stimulant drugs to elicit discriminative stimulus effects. These results suggest that gabapentinoids alter the potency of MOR agonists and stimulant drugs to elicit discriminative stimulus effects via blockade of α₁-VGCCs. SIGNIFICANCE STATEMENT: Prescriptions for gabapentinoids (gabapentin and pregabalin) increased significantly during the opioid epidemic. Using (±)-BAY-K-8644, a dihydropyridine-type agonist at the α₁-subunit of the voltage-gated calcium channel (α₁-VGCC), this study reports that in male and female rats, gabapentinoids increase the potency of fentanyl and heroin and decrease the potency of cocaine and d-methamphetamine to elicit discriminative stimulus effects via blockade of dihydropyridine-binding sites on α₁-VGCC. These results suggest that actions of drugs at α₁-VGCCs contribute to the opioid epidemic and opioid/stimulant co-use.

Neuropeptide G protein-coupled receptors (GPCRs) are membrane protein receptors with 7 transmembrane helices, regulating physiological processes like reproduction, development, and behavior. However, little is known about neuropeptide GPCRs in marine benthic invertebrates. To explore the GPCR composition and potential neuropeptide GPCRs involved in larval development, we performed a genome-wide search of neuropeptide GPCR family genes in the echiuran worm Urechis unicinctus, a marine benthic burrowing Annelida with typical larval settlement and metamorphosis processes during the larval development. A total of 71 putative neuropeptide GPCR genes were identified including 60 family-A GPCRs and 11 family-B GPCRs. Both families contained the conserved 7-transmembrane domain, with family-B GPCRs evolving more conservatively. The clustering of family-A GPCRs formed a large central cluster, where 12 GPCR genes were likely ancestral genes in the evolution of this family. About one-third of neuropeptide GPCR genes were highly expressed in embryos, larvae and adult organs of U. unicinctus. However, the specific GPCRs involved in larval development and adult organ function may differ. In addition, the binding of several neuropeptide GPCRs to larval settlement-related mature peptides was predicted by AlphaFold3 docking. The dual luciferase reporter gene assay showed that the affinity of neuropeptide GPCR Uu-A25 to MIP2 was higher than that to MIP1 in U. unicinctus. Inhibitor (H89 and calmidazolium) and activator (forskolin and Bay K 8644) experiments proved that the cAMP and Ca²⁺ pathways, mediated commonly by neuropeptide GPCRs, play important roles in the regulation of the larval settlement of U. unicinctus. This study provides a better understanding of neuropeptide GPCR evolution in marine benthic invertebrates and provides fundamental data for future functional exploration of the specific neuropeptide GPCRs in U. unicinctus larval development.