Low‐efficacy mu‐opioid receptor (MOR) agonists represent promising therapeutics, but existing compounds (e.g., buprenorphine, nalbuphine) span a limited range of low MOR efficacies and have poor MOR selectivity. Accordingly, new and selective low‐efficacy MOR agonists are of interest. A novel set of chiral C9‐substituted phenylmorphans has been reported to display improved MOR selectivity and a range of high‐to‐low MOR efficacies under other conditions; however, a full opioid receptor binding profile for these drugs has not been described. Additionally, studies in mice will be useful for preclinical characterization of these novel compounds, but the pharmacology of these drugs in mice has also not been examined. Accordingly, the present study characterized the binding selectivity and in vitro efficacy of these compounds using assays of opioid receptor binding and ligand‐stimulated [35S]GTPɣS binding. Additionally, locomotor effects were evaluated as a first step for in vivo behavioral assessment in mice. The high‐efficacy MOR agonist and clinically effective antidepressant tianeptine was included as a comparator. In binding studies, all phenylmorphans showed improved MOR selectivity relative to existing lower‐efficacy MOR agonists. In the ligand‐stimulated [35S]GTPɣS binding assay, seven phenylmorphans had graded levels of sub‐buprenorphine MOR efficacy. In locomotor studies, the compounds again showed graded efficacy with a rapid onset and ≥1 h duration of effects, evidence for MOR mediation, and minor sex differences. Tianeptine functioned as a high‐efficacy MOR agonist. Overall, these in vitro and in vivo studies support the characterization of these compounds as MOR‐selective ligands with graded MOR efficacy and utility for further behavioral studies in mice.
Subchronic PCP administration results in a specific hypermethylation in the Pvalb promoter which may contribute to parvalbumin deficits in this animal model of psychosis.
In the current study we investigated the efficacy of donepezil, risperidone and selective nicotinic α7 and α4β2 receptor agonists to reverse a delay-induced deficit in recognition memory. Adult female hooded-Lister rats received drug treatments and were tested in the novel object recognition (NOR) task following a 6 hour inter-trial interval (ITI). In all treatment groups there was no preference for the left or right identical objects in the acquisition trial. In the retention trial vehicle, risperidone (0.16mg/kg), PNU-282987, an α7 agonist (5mg/kg) and RJR-2403, an α4β2 agonist (1mg/kg) treated rats were unable to discriminate between the novel and familiar objects following a 6 hour ITI. In contrast, donepezil (1.0mg/kg), PNU-282987 (10mg/kg) and RJR-2403 (0.1mg/kg) treated rats spent significantly more time exploring the novel compared to the familiar object following the 6 hour ITI, indicative of enhanced cognitive performance (P<0.05-P<0.01). Interestingly, these compounds were efficacious when administered either before the acquisition or the retention trial of the task, suggesting an important role for nicotinic receptor subtypes in the formation and retrieval of recognition memory.
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