An Assessment of the Role of Opioid Receptors in the Response to Cannabimimetic Drugs

Abstract

Cannabimimetic drugs have been shown to inhibit adenylate cyclase activity in NI8TG2 neuroblastoma cells. This investigation examines the possible role of opioid receptors in the cannabimimetic response. Opioid receptors of the δ subtype were found on N18TG2 membranes using [3H]D‐Ala2‐D‐Leu5‐enkephalin. No δ or K receptors were detected using selective ligands for these sites. The δ binding affinity and capacity were unaltered by cannabimimetic drugs. To test if cannabimimetic drugs may modulate opioid effector mechanisms, cyclic AMP metabolism was determined in intact cells and in membranes. N18TG2 adenylate cyclase was inhibited by the cannabimimetic drugs Δ9‐tetrahydrocannabinol and desacetyllevonantradol, and by the opioid agents morphine, etorphine, and D‐Ala2‐Met5‐enkephalinamide. The opioid inhibition was reversed by naloxone and naltrexone; however, the cannabimimetic response was unaffected. Both cannabimimetic and opioid drugs decreased cyclic AMP accumulation in intact cells, but opioid antagonists blocked the response only to the latter. Thus, cannabimimetic effects are observed even though opioid receptors are blocked by antagonist drugs. The interaction between desacetyllevonantradol and etorphine was neither synergistic nor additive at maximal concentrations, suggesting that these two drugs operate via the same effector mechanism. Other neuronal cell lines having an opioid response were also examined. The cannabimimetic inhibition of cyclic AMP accumulation in NG108‐15 neuroblastoma x glioma cells was not as great as the response in N18TG2. N4TG1 neuroblastoma cells did not respond to cannabimimetic drugs under any conditions tested. Thus, the cannabimimetic inhibition of adenylate cyclase is not universally observed, and the efficacy of the cannabimimetic response does not correlate with the efficacy of the opioid response.

Inhibitory interaction of cannabinoid CB1 receptor and dopamine D2 receptor agonists on voltage-gated currents of goldfish cones

“…The number of cells recorded for each condition is indicated in parenthesis above each histobar. opioid agonists (Devane et al, 1986;Childers et al, 1992;Shapira et al, 1998) as well as combined CB1 and D2 agonists (Meschler & Howlett, 2001), suggesting convergence of signal-transduction mechanisms on adenylate cyclase. Two interpretations of these results are that (1) the receptor-activated Gi0o protein transduction cascades shares the same pool of adenylate cyclase, or (2) the receptor systems activate the same pool of Gi0o proteins that ultimately regulate adenylate cyclase (Meschler & Howlett, 2001;Mukhopadhyay et al, 2002).…”

Mouse Neuroblastoma CB1 Cannabinoid Receptor-Stimulated [35S]GTPɣS Binding: Total and Antibody-Targeted Gα Protein-Specific Scintillation Proximity Assays

“…Some neuroblastoma cloned lines were shown to synthesize neuropeptides, such as met-enkephalin (N1E-115 and the NG108-15 hybrid cells) (Gilbert, Knodel, Stenstrom, & Richelson, 1982; Glaser, Hubner, & Hamprecht, 1982), or vasoactive intestinal peptide by N1E-115, NS20, and N18TG2 clones and NG108-15 hybrid cells (Brick, Howlett, & Beinfeld, 1985; Glaser, Besson, Rosselin, & Hamprecht, 1983; Said & Rosenberg, 1976). When selected and subcloned for thioguanine resistance, N18TG2 and N4TG1 cells were useful for hybridization with either the rat C6BU1 bromouridine deoxyribose (BUdR)-resistant glioma (NG108-15) (Gilman & Minna, 1973; Hamprecht, 1977; Klee & Nirenberg, 1974), and these hybrid cells have been utilized for studies of CB 1 receptors (Devane, Spain, Coscia, & Howlett, 1986; Howlett, Qualy, & Khachatrian, 1986; Mackie, Devane, & Hille, 1993). N18TG2 cells have also been used to “immortalize” neurons by hybridization: with mesencephalic neurons (MN9D) (Choi et al, 1991), which have been used for studies of interactions between CB 1 cannabinoid and D 2 dopamine receptors (Calipari et al, 2014; Eldeeb, Leone-Kabler, & Howlett, 2016); dorsal root ganglia cells (F-11) (Cruciani, Dvorkin, Morris, Crain, & Makman, 1993; Francel et al, 1987; Platika, Boulos, Baizer, & Fishman, 1985), which have been used for investigation of the endocannabinoid system (Fan et al, 2011; Fioravanti et al, 2008; Rimmerman et al, 2008; Ross et al, 2001) and other reports; and spinal cord neurons (NSC-34) (Cashman et al, 1992), which have been used for studies of neuroprotection by cannabinoids (Moreno-Martet et al, 2012).…”

Signal Transduction via Cannabinoid Receptors

“…Opioid and cannabinoid receptors share similar signal transduction pathways involving Gi/o-mediated inhibition of adenylyl cyclase and a decrease in cAMP concentrations in the striatum [29–31]. CB 1 and μ-opioid receptors are colocalized on axons and dendrites and also share trans-synaptic interactions within striatal patch GABAergic neurons and within the shell of the nucleus accumbens [32,33].…”

“…Effects of Δ 9 -THC [36] but not the highly efficacious CB 1 agonist desacetyllevonanatradol (DALN) [29] were reported for δ-opioid receptor binding. In a neuronal cell line endogenously expressing both CB 1 and δ-opioid receptors, no pharmacological interactions were observed between receptors for the Gi-mediated inhibition of adenylyl cyclase [29].…”

“…In a neuronal cell line endogenously expressing both CB 1 and δ-opioid receptors, no pharmacological interactions were observed between receptors for the Gi-mediated inhibition of adenylyl cyclase [29]. However, the observation that a ceiling on the maximal inhibition could be obtained upon stimulation of both receptor types suggests the existence of shared components of the signal transduction module (such as the G-proteins or the effectors) limiting responses when both receptor types were stimulated [29]. Detailed investigation indicated that endogenously expressed CB 1 and δ-opioid receptors in a neuronal cell do not acutely regulate the same G-proteins [39,40].…”