The Cannabinoid CB1 Receptor Inverse Agonist/Antagonist SR141716A Activates the Adenylate Cyclase/PKA Signaling Pathway Among Other Intracellular Emetic Signals to Evoke Vomiting in Least Shrews (Cryptotis parva)

Intracellular emetic signals involved in the cannabinoid CB₁ receptor inverse agonist/antagonist SR141716A were investigated. SR141716A (20 mg/kg, i.p.)-evoked vomiting occurred via both the central and peripheral mechanisms. This was accompanied by robust emesis-associated increases in the following: (i) c-<i>fos</i>- and phospho-glycogen synthase kinase-3α/β (p-GSK-3αβ)-expression in the shrew's dorsal vagal complex (DVC), (ii) phospho-extracellular signal-regulated kinase1/2 (p-ERK_1/2) expression in both the DVC and jejunal enteric nervous system, and (iii) time-dependent upregulation of cAMP levels and phosphorylation of protein kinase A (PKA), protein kinase B (Akt), GSK-3α/β, ERK_1/2, and protein kinase C αβII (PKCαβII) in the brainstem. SR141716A-evoked emetic parameters were attenuated by diverse inhibitors of the following: PKA, ERK_1/2, GSK-3, phosphatidylinositol 3-kinase (PI3K)-Akt pathway, phospholipase C (PLC), PKC, Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), L-type Ca²⁺ channel (LTCC), store-operated Ca²⁺ entry (SOCE), inositol trisphosphate receptor (IP3R), ryanodine receptor (RyRs), both 5-HT₃-, and D_2/3-receptor antagonists, and the transient receptor potential vanilloid 1 receptor (TRPV1R) agonist. SR141716A appears to evoke vomiting via inverse agonist activity involving emesis-associated kinases, including cAMP/PKA, ERK_1/2, PI3K/Akt/GSK-3, PLC/PKCαβII, and CaMKII, which depend upon Ca²⁺ mobilization linking extracellular Ca²⁺ entry via plasma membrane Ca²⁺ channels (LTCC, SOCE, TRIPV1R) and intracellular Ca²⁺ release via IP3Rs and RyRs. The 5-HT₃, NK₁, and D_2/3 receptors also contribute to SR141716A-mediated vomiting.