In search of a backup M2 muscarinic receptor antagonist to the previously reported compound 1, we discovered compound (+)-14, which showed superior oral efficacy in animal models. The improvement of oral efficacy was achieved by modulating both the molecular weight and lipophilicity of the lead compounds.
Orphanin FQ/nociceptin (OFQ/N) is the endogenously occurring peptide ligand for the nociceptin opioid receptor (NOP) that produces anxiolytic-like effects in mice and rats. The present study assessed the anxiolytic-like activity of 8-[bis(2-methylphenyl)-methyl]-3-phenyl-8-azabicyclo[3.2.1]octan-3-ol (SCH 221510), a novel potent piperidine NOP agonist (EC50 = 12 nM) that binds with high affinity (Ki = 0.3 nM) and functional selectivity (>50-fold over the μ-, κ-, and δ-opioid receptors). The anxiolytic-like activity and side-effect profile of SCH 221510 were assessed in a variety of models and the benzodiazepine, chlordiazepoxide (CDP), was included for comparison. The effects of chronic dosing of SCH 221510 were also assessed. Furthermore, the specificity of the anxiolytic-like effect of SCH 221510 was investigated with the NOP receptor antagonist 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J-113397) and the opioid receptor antagonist naltrexone. Like CDP (1–30 mg/kg i.p.), SCH 221510 (1–30 mg/kg p.o.) produced anxiolytic-like effects in the elevated plus-maze (rat and gerbil), Vogel conflict (rat), conditioned lick suppression (rat), fear-potentiated startle (rat), and pup separation-induced vocalization (guinea pig) assays. In the Vogel conflict, the anxiolytic-like effect of SCH 221510 (10 mg/kg) was attenuated by J-113397 (3–10 mg/kg p.o.), but not naltrexone (3–30 mg/kg i.p.). Additionally, the anxiolytic-like effects of SCH 221510 did not change appreciably following 14-day b.i.d. dosing in rats (10 mg/kg). Furthermore, unlike CDP, SCH 221510 (3–30 mg/kg) produced anxiolytic-like activity at doses that did not disrupt overt behavior. Collectively, these data suggest that NOP agonists such as SCH 221510 may have an anxiolytic-like profile similar to benzodiazepines, with a reduced side-effect liability.
Squirrel monkeys were trained to discriminate either the nonselective adenosine analog 5'-N-ethylcarboxamide adenosine (NECA) or the A1-selective analog N6-cyclopentyladenosine (CPA) from saline. After i.v. injections of 0.03 mumol/kg of NECA or 1.0 mumol/kg of CPA, 10 consecutive responses on one lever produced food, whereas after i.v. injections of saline, 10 consecutive responses on the alternate lever produced food. The discriminative-stimulus effects of the adenosine analogs NECA, CPA, 2-chloroadenosine and the R- and S-isomers of N6-phenylisopropyladenosine (PIA), of the adenosine antagonists caffeine and 8-cyclopentyltheophylline (CPT), and of selected drugs from other classes (haloperidol, pentobarbital, diazepam and morphine) were determined by administering cumulative doses i.v. before sequential components of the experimental session. All adenosine analogs engendered dose-related increases in the percentage of responses on the NECA- or CPA-associated levers reaching a maximum of greater than or equal to 90%. The rank order of potency was similar in both NECA-trained and CPA-trained monkeys: NECA greater than 2-chloroadenosine greater than or equal to CPA greater than or equal to R-PIA greater than S-PIA. None of the other drugs had discriminative-stimulus effects comparable to those of the adenosine analogs. In additional studies, the nonselective adenosine antagonist caffeine or the A1-selective antagonist CPT were administered before cumulative doses of NECA or CPA. Both adenosine antagonists blocked the discriminative-stimulus effects of NECA and CPA, with CPT being about one order of magnitude more potent than caffeine.(ABSTRACT TRUNCATED AT 250 WORDS)
The present study investigated whether blockade of conditioned avoidance responding (CAR) in rats by selective D1 and D2 receptor antagonists could be differentially affected by anticholinergics. The results show that atropine and scopolamine dose-relatedly antagonized the effects on CAR of two specific D2 receptor blockers, haloperidol and raclopride, but potentiated the effects of three specific D1 receptor antagonists, SCH 23390, SCH 39166 and NO-01-0756. Of the less specific dopamine receptor antagonists tested, scopolamine blocked the effects of clozapine and cis-flupenthixol, but did not alter the effects of chlorpromazine, thioridazine or cis-piflutixol. Although the mechanisms involved in the differential shifts by the anticholinergics are unknown, the results are consistent with the view that CAR antagonism by the specific D2 vs. D1 receptor antagonists involves unique and separate mechanisms of action. With respect to the less specific dopamine receptor antagonists, the CAR blockade seen with clozapine and cis-flupenthixol might reflect predominant D2 receptor blockade because their effects were blocked by atropine. In contrast, the CAR blockade by chlorpromazine, thioridazine and cis-piflutixol antagonists might be mediated by equal degrees of D1 and D2 receptor blockade inasmuch as they were not blocked or potentiated by atropine. The antagonism of CAR in rats by the D1 receptor antagonists suggests that these drugs have potential antipsychotic activity in humans. However, they do not appear to enhance central cholinergic transmission and therefore may be devoid of the side effects produced by the antipsychotics in clinical use.
